[ Up ]   [ Home ]   [ Projects ]   [ Publications ]   [ Gallery ]   [ Teaching ]

Publications 1980 - 1989

2000 -

1990 - 1999

1980 1981 1982 1983 1984 1985 1986 1987 1988 1989

1977 - 1979


1989

  1. Antos-L; Pardavi-Horvath-M; Cziraki-A; J. Fidler; P. Skalicky
    "Microstructure of yttrium iron garnet thin films and of gadolinium gallium garnet single crystals"
    Journal of Crystal Growth. vol.94, no.1; Jan. 1989; p.197-202
    [ Abstract]
    The microstructure of Y3Fe5O12 (YIG) based magnetic garnet thin films and of single crystalline Gd3Ga5O12 (GGG) were studied (GaSm:YIG, CaGeSm:YIG, GGG, GGG doped with Ca) by transmission electron microscopy. Non-spherical particles, small precipitates with weak diffraction contrast and line defects were found by conventional TEM. The increase in the distance of lattice planes near line defects was observed by high resolution electron microscopy.

  2. J. Fidler; Knoch-KG; H. Kronmüller; Schneider-G
    "Analytical TEM study of Al-doped, 'two-phase' Nd-Fe-B sintered magnets"
    Journal of Materials Research. vol.4, no.4; July-Aug. 1989; p.806-14
    [ Abstract]
    The microstructure and the coercivity of sintered Nd20Fe(73.5-x)B6.5Alx (x=0, 2.5) permanent magnets are influenced by the Al concentration. In Al-containing magnets the authors found a homogeneous distribution of Al in the hard magnetic phase and the occurrence of an intergranular Nd(Fe,Al)2 phase between the hard magnetic grains. Their analytical TEM study revealed that in 'Al2O3-doped' magnets the crystal structure of the Nd-rich intergranular phase partly changes from FCC (a=0.52 nm) to HCP (a=0.39 nm, c=0.61 nm), whereas the content of iron simultaneously decreases from 5-10 at.% to 1.5-4 at.%. A platelet-shaped phase, embedded in the Nd-rich intergranular phase, was determined as a Nd5Fe2(B,O)x phase. The influence of the microstructure on the coercivity in Al-doped magnets is discussed.

  3. J. Fidler; Knoch-KG
    "Electron microscopy of Nd-Fe-B based magnets"
    J. Magn. Magn. Mater. vol.80, no.1; Aug. 1989; p.48-56
    [ Abstract]
    Transmission electron microscopy has been used widely to characterize the complex multiphase microstructure of Nd2Fe14B based permanent magnets. The grain size of the magnets strongly depends on the processing technique. A study of sintered magnets revealed two types of grain boundaries: on e containing no intergranular phase between hard magnetic grains and one composed of nonmagnetic Nd-rich phases. In doped sintered magnets the dopant is dissolved in the hard magnetic phi -phase. In the case where the solubility of the dopant is low at the sintering temperature (Nb, Mo, Zr), precipitates are formed within the phi -phase. Dopants also form new intergranular phases and influence the wetting of the liquid phase and the smoothness of the surface of the phi -grains during sintering and therefore affect the coercivity.

  4. Josef Fidler,
    "On the role of microstructure on coercivity of rare earth permanent magnets",
    Proceedings of VII. Int. Seminar on Magnetism, Dreseden, DDR, April 1989, p.24.

  5. J.Fidler and K.G.Knoch,
    "The influence of dopants on microstructure and coercivity of Nd-Fe-B sintered magnets",
    Proceedings of X. Int. Workshop on rare earth magnets and their applications, Kyoto, Japan, May 1989, (proceedings Book by: The Society of Non-Traditional Technology, Toranomon Kotohira-kaikan Bldg. 3F, 1-2-8 Toranomon, Minatu-Ku. Tokyo 105, Japan), Vol.2, p. 283.

  6. K.G.Knoch, G.Schneider, J.Fidler, E.-Th. Henig, H.Kronmüller,
    "Al-doped Nd-Fe-B permanent magnets: wetting and microstructural investigations",
    IEEE Transactions on Magnetics, Volume: 25 Issue: 5, Sept. 1989, 3426 - 3428.
    [ Abstract ], [ PDF ]
    © 1989 IEEE see copyright notice

  7. Knoch-KG; Bischoff-E; Henig-E-T; J. Fidler
    "Analytical TEM study of cast Nd80-Fe15-B5 alloys"
    Materials-Letters. vol.8, no.8; Aug. 1989; p.301-4
    [ Abstract]
    Controversial results on the microstructure of cast Nd80-Fe15-B5 alloys have been reported. The investigations revealed a microstructure consisting of three phases: the hard-magnetic Phi phase, the platelet-shaped boride phase ( rho ) Nd5Fe2B6, identical with the one found in Nd20-Fe73.5-B6.5 sinter magnets which is embedded within the FCC-Nd phase. A new phase with a Nd:Fe ratio of 1:1.1 was found.


1988

  1. J.Fidler and Y.Tawara,
    "TEM-study of the precipitation of iron in Nd-Fe-B sintered magnets",
    IEEE Transactions on Magnetics, Volume: 24 Issue: 2 Part: 2, March 1988, 1951 - 1953.
    [ Abstract ], [ PDF ]
    © 1988 IEEE see copyright notice

  2. J. Fidler
    "Analysis of SmCo 2:17 sintered magnets by electron diffraction"
    Journal of Applied Physics. vol.64, no.10, pt.2; 15 Nov. 1988; p.5735
    [ Abstract]
    Summary form only given, as below. Precipitation-hardened SmCo 2:17 sintered magnets contain a multiphase, cellular microstructure, which is determined by nominal composition and heat treatment parameters. A correlation between microstructure and coercivity has been shown by transmission electron microscopy (TEM). Magnets with different samarium content were investigated. In magnets with iHc<700 kA/m a high density of basal stacking faults (microtwinning) within the hard magnetic, rhombohedral 2:17 phase was shown. Local changes of crystal lattice parameters are observed in low coercivity magnets. Calculated diffraction patterns of CaCu5-, TbCu7-, Th2Zn17-, and Th2Ni17-crystal structures with different types of atomic occupancies are compared with experimental electron diffraction patterns obtained by TEM. The study revealed that the local composition within the hard magnetic grains influences the precipitation structure which is necessary for achieving magnetic hardness by domain wall pinning.

  3. Josef Fidler,
    "Electron microscopy in the development of new magnetic materials",
    Proceedings IX. European Congress on Electron Microscopy (EUREM), York, England, September 1988, Inst.Phys.Conf.Ser.No.93,Vol.2,(1988),p.211.

1987

  1. J. Fidler
    "On the role of the Nd-rich phases in sintered Nd-Fe-B magnets"
    IEEE-Transactions-on-Magnetics. vol.MAG-23, no.5, pt.1; Sept. 1987; p.2106-8
    [ Abstract]
    Sintered Nd15-Fe77-B8 magnets contain a multiphase microstructure. The authors' analytical transmission electron microscope study reveals that the Nd-rich phase, which is an essential part of the liquid phase sintering process can be divided into at least 4 sub-types with different Nd:Fe-ratios. Impurities of the raw material such as Nd-oxides and Nd-chlorides are randomly found in magnets, partly in the form of small inclusions up to 500 nm diameter within 2:14:1-hard-magnetic grains and partly in the form of large grains up to several microns diameter. As consequence of this analytical study a high concentration of boron vacancies as well as iron vacancies, especially in grain boundary regions is proposed. They have found that the degree of continuity of the intergranular Nd-rich phase is proportional to the intrinsic coercivity of the magnet. The intrinsic coercivity of sintered Nd-Fe-B magnets is determined by the nucleation of reversed domains and by the expansion of the reversed nuclei, which is hindered by the non-magnetic Nd-rich oxide grain boundary layer phase.

  2. Ghandehari-MH; J. Fidler
    "Microstructural studies of high coercivity Nd15Fe77B8 sintered magnets"
    High Performance Permanent Magnet Materials Symposium. Mater. Res. Soc, Pittsburgh, PA, USA; 1987; xix+343 p.193-201
    [ Abstract]
    Microstructures of Nd15-xDyxFe77B8 prepared by alloying with Dy, and by using Dy2O3 as a sintering additive, have been determined using electron microprobe and transmission electron microscopy. The results have shown a higher Dy concentration near the grain boundaries of the 2-14-1 phase for magnets doped with Dy2O3, as compared to the Dy-alloyed magnets. A two-step post sintering heat treatment was also studied for the two systems. The resultant concentration gradient of Dy in the 2-14-1 phase of the oxide-doped magnets is explained by the reaction of Dy2O3 with the Nd-rich grain boundary phase and its slow diffusion into the 2-14-1 phase. Increased Dy concentration near the grain boundary is more effective in improving the coercivity, as domain reversal nucleation originates at or near this region.

  3. J. Fidler; J. Bernardi; P. Skalicky
    "Analytical electron microscope study of high- and low-coercivity SmCo 2:17 magnets"
    High Performance Permanent Magnet Materials Symposium. Mater. Res. Soc, Pittsburgh, PA, USA; 1987; xix+343 p.181-92
    [ Abstract]
    Sintered, precipitation hardened SmCo 2:17 magnets contain a multiphase microstructure. Electron microscopic investigations reveal that the size of the rhombic, cellular precipitation structure and the formation of cell interior and cell boundary phases is determined by the nominal composition of the alloy and the postsintering heat treatment conditions and primarily control the intrinsic coercivity of the magnet. Selected area electron diffraction together with high resolution electron microscopy showed a high density of basal stacking faults (microtwinning) of the cell interior phase of low coercivity (iHc<700 kA/m) magnets with a (c/a)*- ratio of the basic structural unit of >0.843. High coercivity magnets (iHc>1000 kA/m), containing a high density of the platelet phase perpendicular to the c-axis, exhibit cell diameters up to 200 nm with a (c/a)*-ratio of the basic structural unit of the cell interior phase of <0.843.

  4. Ghandehari-MH; J. Fidler
    "Microstructural evidence for the magnetic surface hardening of Dy2O3-doped Nd15Fe77B8 magnets"
    Materials-Letters. vol.5, no.7-8; July 1987; p.285-8
    [ Abstract]
    Microstructures of (NdDy)15Fe77B8 prepared by alloying with Dy, and using Dy2O3 as a sintering additive, have been determined using electron microprobe and transmission electron microscopy. A two-step, post-sintering heat treatment has been applied to both systems in order to improve the coercivity. The results show that the second-step heat-treatment temperature is lower for the oxide-doped magnets for an optimum intrinsic coercivity. In a typical Dy2O3-doped sample, a high concentration of Dy was found close to the grain boundary of the hard 2-14-1 phase. In contrast, Dy was found uniformly substituted in a magnet to which Dy was added in the alloying step. It is proposed that a high concentration of Dy at the surface of the (NdDy)2Fe14B improves the coercivity by increasing the required field for domain reversal nucleation at or near the grain boundaries.

  5. Pfutzner-H; J. Fidler
    "Magnetic measuring and analysis techniques: investigations on soft magnetic materials"
    Elektrotechnik-und-Maschinenbau. vol.104, no.2; Feb. 1987; p.41-9
    [ Abstract]
    Discusses modern methods for recording hysteresis loops, dynamic magnetization loops, remagnetization losses (electronic integrators are used in conjunction with minicomputers for the continuous recording of graphs) and nondestructive methods of domain analysis, with special reference to the analysis of transformer sheets, using the electron scan microscope or special, cheaper colloid techniques.

  6. Parker-SFH; Grundy-PJ; J. Fidler
    "Electron microscope study of precipitation in a niobium-containing (Nd, Dy)-Fe-B sintered magnet"
    J. Magn. Magn. Mater. vol.66, no.1; March 1987; p.74-8
    [ Abstract]
    The microstructure of a niobium-containing (Nd, Dy)-Fe-B alloy has been investigated using transmission electron microscopy, STEM and SEM X-ray microanalysis and optical microscopy. Magnetic measurements showed an increase in coercivity when niobium was added to a (Nd, Dy)-Fe-B magnet. The microstructure was found to be similar to that of a ternary Nd-Fe-B magnet but with two additional phases, a Laves Fe2Nb compound and a finely dispersed niobium containing coherent precipitate found in the magnetically hard phase. Lorentz microscopy indicated domain wall interactions with the fine precipitates which may be responsible for the enhanced coercivity of the niobium doped magnet.

  7. Mayer-J; Urban-K; J. Fidler
    "Phase transitions between the quasicrystalline, crystalline, and amorphous phases in Al-16 at.% V"
    Physica-Status-Solidi-A. vol.99, no.2; 16 Feb. 1987; p.467-73
    [ Abstract]
    By means of electron irradiation the amorphous state can be produced in quasicrystalline Al-16 at.% V. The transitions between the quasicrystalline, crystalline, and amorphous phases are studied in situ in a high-voltage electron microscope. Analysis of the diffraction patterns of the amorphous and the quasicrystalline state reveals that both states are characterized by the occurrence of virtually the same basic density wave vectors. In contrast to the case of Al-14 at.% Mn, for which a similar study was published earlier, the quasicrystalline-amorphous transition is not completely reversible.


1986

  1. Urban-K; Mayer-J; Rapp-M; Wilkens-M; Csanady-A; J. Fidler
    "Studies on aperiodic crystals in Al-Mn and Al-V alloys by means of transmission electron microscopy"
    Journal-de-Physique-Colloque. vol.47, no.C-3; July 1986; p.465-75
    [ Abstract]
    Electron microscopy has been used to study quasicrystals and T phases in rapidly cooled Al-14 at.% Mn and Al-16 at.% V. The T phase can also be produced by interdiffusion in evaporated Al/Mn layers. Also in these experiments the authors have observed a new crystalline phase with structural elements related to the aperiodic crystals by a shear parallel to a particular symmetry direction. The phase transitions between the quasicrystalline or the T phase to the crystalline or amorphous phases were studied in situ in a high-voltage electron microscope.

  2. Rao-KV; J. Fidler; Chen-HS
    "Melt-spun Al84V16: a new icosahedral crystal"
    Europhysics-Letters. vol.1, no.12; 15 June 1986; p.647-53
    [ Abstract]
    The authors report the observation of an icosahedral structure in a new alloy system: melt-spun Al84V16. In the as cast alloys, homogeneous large icosahedral grains with an average diameter of about 2 mu m are observed. From high-resolution STEM X-ray analyses the compositional homogeneity in and around the grains is determined. They discuss the structural studies on i(Al-V) in terms of known structures of the related crystalline alloys, and the relevance of a recent modified-projection-approach by Elser (1985) in generating the icosahedral structure from six-dimensional lattice.


1985

  1. Ghandehari-MH; J. Fidler
    "Microstructural studies of oxide doped PrCo5 magnets"
    IEEE-Transactions-on-Magnetics. vol.MAG-21, no.5; Sept. 1985; p.1973-5
    [ Abstract]
    Pr0.8Sm0.2Co5 magnets doped with Cr2O3 have displayed high coercivity similar to SmCo5. Transmission electron microscopy (TEM), electron diffraction, and X-ray microanalysis of a doped magnet showed an absence of grains with high density basal stacking faults, identified as (Pr,Sm)2Co7 and (Pr,Sm)5Co19, whereas microprecipitates of (Pr,Sm)2O3 and CaO were located within the 1-5 grains and near grain boundaries, respectively. The resultant coercivity increase is explained by a model based on the nucleation of reversed domains. Grains with a high density of martensitic transformation twins which occasionally occur in (Pr,Sm)Co5 magnets were identified as (Pr,Sm)Co2.

  2. J. Fidler
    "Analytical microscope studies of sintered Nd-Fe-B magnets"
    IEEE-Transactions-on-Magnetics. vol.MAG-21, no.5; Sept. 1985; p.1955-7
    [ Abstract]
    Various sintered Nd15Fe77B8 permanent magnets supplied by different producers were examined by analytical electron microscopy. An identical microstructure was found in all of the different magnets. Three phases were detected by means of high resolution electron microscopy, electron diffraction, and X-ray microanalysis. Besides the hard magnetic boride phase Nd2Fe14B, a soft magnetic boride phase close to Nd2Fe7B6 and a Nd-rich sintering aid phase (DHCP structure) were identified. The Nd-rich phase preferentially occurs along grain boundaries as a thin layer with about 10-nm thickness. The soft magnetic phases determine the magnetization reversal and limit the coercivity of sintered Nd-Fe-B magnets.

  3. J. Fidler; Luo-Yang
    "Microstructure and coercivity of cast and sintered N-Fe-B magnets"
    Proceedings of the Eighth International Workshop on Rare-Earth Magnets and their Applications and the Fourth International Symposium on Magnetic Anisotropy and Coercivity in Rare Earth- Transition Metal Alloys. Univ. Dayton, Dayton, OH, USA; 1985; xi+793 p.647-56
    [ Abstract]
    Optical microscopy, transmission electron microscopy, X-ray and electron diffraction and X-ray microanalysis have been used to characterize the various phases in cast and sintered Nd-Fe-B magnets after casting and after sintering. The results are correlated with the coercivity of the magnets. The investigations revealed an identical microstructure in various Nd15Fe77B8 magnets, supplied by different producers. Besides the hard magnetic boride phase Nd2Fe14B, a soft magnetic boride phase close to Nd2Fe7B6 and a Nd-rich sintering aid phase were detected in the sintered magnets. In cast magnets additional Fe-phases occurred. Along grain boundaries a thin layer of the Nd-rich sintering aid phase was found. The soft magnetic phases act as nucleation sites for reversed domains and determine the magnetization reversal and therefore limit the coercivity of cast and sintered Nd-Fe-B magnets. It is shown that the intrinsic coercive force of sintered rare earth-iron permanent magnets is determined by the nucleation and expansion field of reversed domains. The magnetically inhomogeneous transition region primarily control the nucleation field of reversed domains.


1984

  1. J. Fidler; P. Skalicky
    "On microstructure and coercivity of rare earth-cobalt magnets"
    1984 Digests of INTERMAG '84. International Magnetics Conference (Cat. No. 84CH1918-2). North-Holland, Amsterdam, Netherlands; iii+546 p.11
    [ Abstract]
    Summary form only given. The authors have undertaken an electron microscope study to show the influence of the microstructure on the magnetic hardness of rare earth-cobalt magnets. For single-phase SmCo5 sinter magnets, the coercivity is determined by the nucleation field and the expansion field of reversed domains. In the precipitation-hardened multiphase Sm2Co17 sinter magnets, the high coercive force is obtained by the pinning of magnetic domain walls at the cell boundaries of a continuous precipitation structure. It is found that the microstructure predominantly determines the origin of high coercive forces, i.e. the nucleation and expansion of reversed domains and the pinning of domain walls.


1983

  1. Rabenburg-L; Mishra-RK; Thomas-G; J. Fidler; P. Skalicky; Rothwarf-F
    "Comments, with reply, on 'High resolution electron microscope study of Sm(Co,Fe,Cu,Zr)7.5 magnets'"
    IEEE-Transactions-on-Magnetics. vol.MAG-19, no.6; Nov. 1983; p.2723-5
    [ Abstract]
    The commenters maintain Fidler et al. have misinterpreted their high-resolution images of the Sm(Co,Cu,Fe,Zr)7.5 alloy (see ibid., MAG-19, no.6, p.2041-3, 1983), and disagree with the conclusions drawn by Fidler et al. from their lattice fringe images.

  2. J. Fidler; P. Skalicky; Rothwarf-F
    "High resolution electron microscope study of Sm(Co, Fe, Cu, Zr)7.5 magnets"
    IEEE-Transactions-on-Magnetics. vol.MAG-19, no.5; Sept. 1983; p.2041-3
    [ Abstract]
    High resolution electron microscopy of a set of Sm(Co.725Fe.20Cu.055 Zr.02)7.5 magnets has been used to characterize the structure and the size of the various microphases present. Investigation of the samples, which were sintered at 1215 degrees C and subsequently isothermally aged in steps of 50 degrees C at temperatures between 700 degrees C and 900 degrees C, and step aged at 400 degrees C, revealed changes in the shape and size of the rhomboid cellular microstructure with aging temperature. Lattice fringe images show the coherent precipitation of the cell boundary phase and of the cell interior phases. The platelet phase, consisting of a hexagonal 2:17 layer, and twin boundaries have been characterized within the cell interiors. It is shown that the intrinsic coercive force is correlated with the morphology of the precipitation structure and depends on the heat treatment of the magnets.

  3. Schattschneider-P; J. Fidler; Chopov-V
    "Energy loss measurements on Co5Sm thin films"
    Vakuum-Technik. vol.32, no.3; April 1983; p.75-80
    [ Abstract]
    Energy loss measurements on Co5Sm thin films performed in a transmission setup reveal a broad, atypical plasmon at 15 eV and faint structure at about 5 eV. The latter is shown to disappear with decreasing grain size and is assumed to correspond to a transition in which (s,d)-hybridized states are involved. Wave number resolved measurements demonstrate that the plasmon peak disperses negatively, in contrast to the usual NFE plasmon behaviour. In order to explain this anomaly it is tentatively proposed that there exists a near lying interband transition, into which the plasmon is hybridized.

  4. J. Fidler
    "Lattice-fringe imaging of precipitation-hardened cobalt rare-earth magnets"
    Philosophical Magazine A (Physics-of-Condensed-Matter,-Defects-and-Mechanical-Properties). vol.47, no.5; May 1983; p.L19-22
    [ Abstract]
    The different microphases of high coercivity (Co, Fe, Cu, Zr)7.5Sm permanent magnets have been studied and characterized by means of high-resolution electron microscopy. From lattice-fringe images of the cellular microstructure the misfit of the crystal lattice parameter between the coherent cell boundary phase and the cell interior phase is determined. It is shown that the platelet phase within the cell interiors consists of a hexagonal Co17Sm2 layer.

  5. J. Fidler; P. Skalicky
    "New materials for permanent magnets"
    Elektrotechnik-und-Maschinenbau. vol.100, no.1; Jan. 1983; p.1-5
    [ Abstract]
    Considerable progress has been made in recent years in the development of new permanent magnet materials. Cobalt prices have reduced the attraction of conventional Al-Ni-Co magnets and these have been replaced by hard ferrites in many applications. Rare earth cobalt magnets are gaining in popularity for cases where optimum magnetic properties are needed. The new Fe-Cr-Co and Mn-Al-C magnets have good workability at low material cost, although their Curie point is low and remanence and coercive field strength thus depend strongly on temperature.

  6. Schattschneider-P; J. Fidler; Chopov-V
    "Wavenumber-resolved energy-loss spectra of Co5Sm"
    Journal of Electron Spectroscopy and Related Phenomena. vol.31, no.1; April 1983; p.25-32
    [ Abstract]
    Wavenumber-resolved spectra of Co5Sm have been obtained by electron energy-loss spectroscopy using 40 kV electrons in the diffraction mode. Four losses are found between 15 and 22 eV which are identified as a volume plasma loss of Co5Sm (15.3 eV), plasma losses modified by carbon contamination (17.3 and 20 eV) and a plasma loss of Sm2O3. The observed features are nondispersive within the surveyed q-space range (O<=q <0.5 AA-1). An interpretation in terms of a plasma loss hybridized by nonvertical interband transitions is proposed.

  7. Pfutzner-H; Schwarz-G; J. Fidler
    "Computer-controlled domain detector"
    Japanese Journal of Applied Physics, Part 1 (Regular Papers & Short Notes). vol.22, no.2; Feb. 1983; p.361-4
    [ Abstract]
    A first approach for detecting the domain configuration of coated Si-Fe sheets by computer-controlled field scanning is considered. A topogram of the domains is plotted, and the physical origin of the detected field components is discussed. Also, stray field topograms of magnetized sheets are presented. These indicate that the field intensity cannot be associated with the angle of misorientation of an individual grain.


1982

  1. Rodewald-W; J. Fidler
    "Improvement of coercivity of (CeMM,Sm)Co5-magnets"
    Proceedings of the 6th International Workshop on Rare Eart-Cobalt Permanent Magnets and Their Applications and 3rd International Symposium on Magnetic Anisotropy and Coercivity in Rare Earth-Transition Metal Alloys. Tech. Univ. Vienna, Vienna, Austria; 1982; xvii+783 p.399-409
    [ Abstract]
    The coercivity of (CeMM,Sm)Co5-magnets can be improved by additions of small amounts of transition metal powders, e.g. Sn, Pb, Zn, Fe, Co, Ni, etc. in combination with one of the hydrides, TiH2, ZrH2, NbH, etc, or powders of alloys, e.g. Fe2Sn, Ni3Sn2, etc. and ZrH2. The increase of coercivity is mainly caused by the impediment of phases with low anisotropy which can act as nucleation centres for reversed domains. This is demonstrated by investigations in a transmission electron microscope.

  2. Rothwarf-F; Tawara-Y; Ohashi-K; J. Fidler; P. Skalicky; Grossinger-R; H. Kirchmary; Shiqiang-Liu; Strnat-KJ
    "Enhancement of coercivity by heat treatment of Sm(Co,Fe,Cu,Zr)7.5 magnets"
    Proceedings of the 6th International Workshop on Rare Eart-Cobalt Permanent Magnets and Their Applications and 3rd International Symposium on Magnetic Anisotropy and Coercivity in Rare Earth-Transition Metal Alloys. Tech. Univ. Vienna, Vienna, Austria; 1982; xvii+783 p.567-83
    [ Abstract]
    Preliminary results of a series of coordinated experiments done at several laboratories are reported. Sets of Sm(Co0.725Fe0.20Cu0.055Zr0.02)7.5 samples were sintered at 1215 C and subsequently aged in steps of 50 C at temperatures, TA, where 700 C <= TA <= 900 C. A nearly parabolic variation of (BH)max with TA was found at room temperature with a maximum of 28.8 MGOe for TA800 C. Hysteresis loops were measured for the range 300K <= T <= 900K to obtain the temperature dependence of 4 pi Is, Br and IHC; The anisotropy field was measured directly by using a singular point detection technique. Electron microscope micrographs show changes in the shape and size of a rhomboid cellular microstructure with aging temperature. The cell boundaries consist of a 1:5 crystal structure and the cell interiors consist of at least two plate shaped 2:17 phases. The intrinsic coercive force shows a dependence on the length and angle of the rhomboid cellular structure.

  3. J. Fidler; P. Skalicky
    "Domain wall pinning in REPM"
    Proceedings of the 6th International Workshop on Rare Eart-Cobalt Permanent Magnets and Their Applications and 3rd International Symposium on Magnetic Anisotropy and Coercivity in Rare Earth-Transition Metal Alloys. Tech. Univ. Vienna, Vienna, Austria; 1982; xvii+783 p.585-97
    [ Abstract]
    The interaction between the microstructure and the magnetic domains determines the coercivity of REPM. The crystal lattice defects and precipitates which act as domain wall pinning centres, are examined in single-phase Co5RE magnets and in precipitation hardened 17:2 magnets using electron microscopy. In single-phase 5:1 magnets the magnetization reversal occurs by nucleation and growth of reversed domains. Grain boundaries are found to act as strong pinning centres for domain walls. The coercivity mechanism of precipitation hardened 17:2 REPM is controlled by domain wall pinning at a continuous copper containing precipitation phase and is interpreted in terms of a micromagnetic theory for domain wall pinning.

  4. J. Fidler
    "Transmission electron microscopy of single-phase Co5Sm permanent magnets"
    Philosophical Magazine B (Physics-of-Condensed-Matter,-Electronic,-Optical-and-Magnetic-Properties). vol.46, no.6; Dec. 1982; p.565-77
    [ Abstract]
    The microstructure and magnetic domain structure of single-phase sintered Co5Sm permanent magnets has been studied by means of transmission electron microscopy. The materials contain coherent inclusions of different sizes within single-crystal Co5Sm grains. Inclusions with diameters less than 200 nm are characterized as Co7Sm2. The bordering alpha fringes correspond to a boundary fault vector of 1/3(1010). Electron-diffraction analysis reveals that the large inclusions (>300 nm) consist of a rhombohedral Co17Sm2 phase. Besides inclusions, grains with numerous fringe patterns perpendicular to the (0001) direction are also observed. These grains contain overlapping stacking faults with different crystallographic shear vectors of the type 1/3(1010). The coercivity of the single-phase Co5Sm magnets is limited by the nucleation of reverse domains at soft magnetic inclusions. It is found that precipitates act as weak pinning centres for domain walls, and grain boundaries as strong ones.

  5. J. Fidler
    "Coercivity of precipitation hardened cobalt rare earth 17:2 permanent magnets"
    J. Magn. Magn. Mater. vol.30, no.1; Nov. 1982; p.58-70
    [ Abstract]
    The influence of the microstructure on the coercivity has been investigated by means of transmission electron microscopy. It is shown that a thin coherent (CoCu)5Sm-cell boundary phase, separating cells of 17:2-crystal structure, acts as a pinning centre for magnetic domain walls. The attractive interaction force is interpreted in terms of a micromagnetic theory for domain wall pinning. The coercive force is determined by the domain wall energy gradient and by the magnetoelastic coupling energy between domain wall stresses and lattice deformation strains. The calculated coercive force due to the lattice mismatch, originated by the cellular coherent precipitation structure is comparable to the experimentally obtained values.

  6. J. Fidler; P. Skalicky
    "Microstructure of precipitation hardened cobalt rare earth permanent magnets"
    J. Magn. Magn. Mater. vol.27, no.2; May 1982; p.127-34
    [ Abstract]
    A transmission electron microscope study of several precipitation hardened cobalt rare earth magnets has been undertaken. The magnets were in peak aged condition and varied in the chemical composition. The studies reveal a fine cellular microstructure. The shape and size of cells depend on the heat treatment and the alloying elements. The cell interiors consist of at least two plate-shaped 17:2 phases and are surrounded by a 5:1 boundary phase. The replacement of zirconium with hafnium does not alter the cellular morphology and also leads to a high coercivity. The coercive force is strongly influenced by the shape and size of the cellular structure as well as by the lattice misfit between the 5:1 and 17:2 phases. The influence of the microstructure on the coercivity is discussed.


1981

  1. J. Fidler; P. Skalicky
    "Lorentz electron microscopy of Co-Sm permanent-magnet materials"
    IEEE-Transactions-on-Magnetics. vol.MAG-17, no.6; Nov. 1981; p.2648-50
    [ Abstract]
    The magnetic domain structure and microstructure of several Co-Sm magnet alloys were examined by transmission electron microscopy. This study reveals that the investigated single-phase magnets exhibit a low defect density within the grains. The coercivity is determined by the nucleation of reverse domains at soft magnetic inclusions. Precipitation-hardened magnets contain a fine-scale precipitation structure. From the wavy nature of the domain walls the authors conclude a strong pinning at the precipitates.

  2. J. Fidler; P. Skalicky
    "Lorentz electron microscopy of amorphous Fe40Ni40B20"
    Applied-Physics-Letters. vol.39, no.7; 1 Oct. 1981; p.573-4
    [ Abstract]
    Using transmission electron microscopy the authors studied changes in the magnetic domain structure during annealing. At room temperatures the domain structure is determined by magnetostatic effects. Cross-tie walls are observed, and the domains vanished at fields of 25 A/cm. After heating the specimen, a two-stage crystallization behavior occurs. The first stage (140-250 degrees C) is identified as primary crystallization of polycrystalline delta /Fe Ni. Further heating (up to 400 degrees C) shows the formation and growth of (Fe Ni)3B spherulites. The domain structure is determined by the crystallization process. Large spherulites exhibit stripe domains and inside of nonspherulite areas magnetization ripple structures occur. Both of the crystallization centers act as pinning sites for domain walls and are sources of increased coercivity in Fe40Ni40B20 amorphous ribbons.

  3. J. Fidler; P. Skalicky
    "Heterogeneous nucleation of precipitates in Co5Sm crystals"
    Philosophical Magazine A (Physics of Condensed Matter, Defects and Mechanical Properties). vol.44, no.2; Aug. 1981; p.427-46
    [ Abstract]
    A transmission electron microscopic investigation has been undertaken of the heterogeneous nucleation of precipitates present in Co5Sm crystals. By means of computer simulation of the displacement fringe contrast, planar extrinsic faults lying on the basal plane and bordered by Frank partial dislocations were identified as Co17Sm2 precipitates which nucleate at prismatic c-edge dislocations. Further nucleation centres, which were also found, are a-edge dislocation dipoles in the basal plane, prismatic a-edge dislocations and c+a screw dislocations. These experimental results are in agreement with calculations according to continuum theory. These show that the strongest interaction exists between precipitates and prismatic dislocations and edge dislocation dipoles in the basal plane. Thus single prismatic edge dislocations, which have the lowest Peierls stress in Co5Sm, are always found to be decorated. Basal dislocations have a weaker interaction and occur also undecorated.

  4. J. Fidler; H. Kirchmary; P. Skalicky
    "Pinning of magnetic domain walls at dislocations and precipitates in Co5Sm crystals"
    Philosophical Magazine B (Physics of Condensed Matter, Electronic, Optical and Magnetic Properties). vol.43, no.5; May 1981; p.765-80
    [ Abstract]
    A Lorentz-electron microscopic investigation of Co5Sm single crystals reveals that the influence of dislocations on the precipitation and on Bloch walls gives an important contribution to the coercive field in Co5Sm. No pinning of domain walls occurs at basal dislocations. The observed strong pinning at prismatic dislocations is due to long-range interactions and is interpreted in terms of a micro-magnetic continuum theory. It is found that for prismatic a-edge dislocations the maximum interaction force on domain walls is about 54 dyn/cm. The deformation strains which occur because of the coherent precipitation of Co7Sm2 and Co17Sm2, create an interaction force on domain walls of the order of magnitude 1*10-5 dyn for a precipitate at the initial stage of precipitation.


1980

  1. J. Fidler; H. Kirchmary; Wernisch-J
    "Homogeneous precipitation in Co5Sm crystals"
    Journal of the Less Common Metals. vol.71, no.2; June 1980; p.245-57
    [ Abstract]
    The microstructure of Co5Sm crystals shows evidence of continuous precipitation with homogeneous nucleation centres of Co7Sm2 as well as Co17Sm2. The nucleation and growth mechanism, which is dependent on the lowering rate of the crystals, indicates that Co5Sm does not decompose by a classic eutectoidal transformation. Transmission electron microscopy and microprobe analyses show regions with an inhomogeneity of the samarium concentration within and specially near the interphase boundaries of the coherently precipitated Co7Sm2 and Co17Sm2 phases. This exsolution reaction as well as the low free nucleation energy and the relatively high free activation energy below 800 degrees C for the diffusion process determine the magnetic properties such as the initial susceptibility and the temperature dependence of the coercive force in Co5Sm crystals.

  2. J. Fidler; H. Kronmüller
    "Nucleation of reversed domains at Co7Sm2-precipitates in Co5SM crystals"
    J. Magn. Magn. Mater. vol.15-18, pt.3; Jan.-March 1980; p.1461-3
    [ Abstract]
    The change of domain structure by external fields is discussed on the basis of micromagnetism. The intrinsic coercive field is interpreted due to randomly distributed lattice defects and the Peierls potential. The nucleation of reversed domains has been observed in the interphase boundaries between Co7Sm2 and Co5Sm.


Copyright notices

IEEE

Copyright notice

Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE. 

IoP

The Institute of Physics
Journals
Journal of Physics D: Applied Physics

AIP

Journal of Applied Physics
Copyright notice

Copyright American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.


[ Up ]   [ Home ]   [ Projects ]   [ Publications ]   [ Gallery ]   [ Teaching ]
webmaster: josef.fidler (at) tuwien.ac.at
Sept. 2004