J.M. Elbicki

Metal‐bonded Sm2Fe17‐N‐type magnets

A number of metal‐bonded Sm2Fe17‐N magnets have been fabricated. These magnets exhibit iHc = 5.1–17.0 kOe, Br = 6.4–8.4 kG, (BH)max=5.0–10.8 MGOe, Tc = 757 K, and ρ=6.2–6.7 g/cm3. Powder metallurgical techniques have been employed with a mixture of powdered Sm2Fe17‐N and Zn, Sn, or In. Heat treatment is carried out in the temperature range of 160–450u2009°C in a N2 atmosphere at pressures ranging from 0–900 psi. The effects of Zn, Sn, and In contents and heat treatment conditions on the magnetic properties have been studied. Zn as the binder significantly enhances the coercivity iHc from 1.8–2.5 kOe for Zn‐free magnets to 5–17 kOe for 9–20‐wt.u2009% Zn‐containing magnets. The Fe‐Zn phase, FeZn4, and/or Fe3Zn7, formed during heat treatment, may play an important role in producing a high coercivity. Sn‐bonded magnets exhibit significant coercivity, whereas the In‐bonded materials do not. The coercivity behavior is discussed in terms of the chemistry of the system.

Magnetic and structural properties of SmTiFe11-xCox alloys

Abstract SmTiFe11-xCox (0⩽x⩽11) alloys were synthesized and studied by X-ray, SEM, EDXS and magnetometry at fields up to 90 kOe in the temperature range of 4.2–1100 K. It is established that almost single-phase materials exhibiting a ThMn12 type structure can be formed only for x

AC susceptibility measurements in some RTiFe11-xCox (R = Dy, Ho, Er) compounds: Spin-reorientation behavior

The DyTiFe11 - xCox (x = 0, 1, 3), HoTiFe11 - xCox (x = 0, 3) and ErTiFe11 compounds, all exhibiting the T hMn12-type structure, were studied for their ac susceptibility in the temperature range 20–300 K. The Dy- and Ho-containing compounds exhibited spin reorientation from axial to cone to planar, or from axial to cone in the temperature range 250-50 K, as expected. In this structure Dy and Ho with negative second-order Stevens coefficients (αJ < 0) favor planar rare earth sublattice anisotropy, while Fe and Co sublattices favor uniaxial and planar anisotropies, respectively and would be in competition as a function of temperature. A spin-reorientation type of behavior was also observed in the ErTiFe11 compound near 50 K. This observation appears to imply that, in this compound, the higher-order crystal-field terms are important. The magnetization data revealed that in these systems the rare earth and transition metal sublattices coupled antiparallel, as is normally the case in the heavy rare-earth-transition-metal compounds.

Magnetic properties of (Sm1-xRx)2Fe17Ny (R = Ce, Nd and mischmetal)

Abstract (Sm1-xRx)2Fe17 intermetallics, where R is Ce, Nd or mischmetal, have been found to absorb substantial amounts of nitrogen. Single phase systems exist over the composition range from x = 0 to 0.8 for Ce and Nd and x = 0 to 0.2 for mischmetal. Upon nitrogenation, the unit cell volume, magnetization and Curie temperature increase substantially in all these systems. More importantly, the basal plane anisotropy of the parent phases changes to an axial direction. Room temperature anisotropy fields range from 37 to 120 kOe. These materials have the potential for the fabrication of inexpensive bonded permanent magnets.

Magnetic studies of (Gd1−xMx)5Si4 alloys (M=La or Y)

In 1967, Holtzberg, Gambino, and McGuire [J. Phys. Chem. Solids 28, 2283 (1967)] observed that intermetallic Gd5Si4 exhibits TC = 336 K. This is remarkable in that the TC of Gd (∼291 K) is increased by chemical union with a nontransition metal, which is rare, if not unique. In the present study, magnetization‐temperature behavior of Gd5Si4 and (Gd1−xMx)5Si4 systems with M=La or Y were studied and compared with the Brillouin function (BF) to see if molecular‐field theory is obeyed. Demagnetization near TC is much sharper for the alloys than expected from the BF. As examples, at T/TC = 0.9, the BF for Gd5Si4 gives M/M0 = 0.38, whereas the observed values range from 0.99 [for (Gd0.8Y0.2)5Si4] to 0.5 [for (Gd0.6La0.4)5Si4]. The factors responsible for these strong deviations from the BF and the high‐TC values of these alloys are as yet unclear. X‐ray patterns for yttrium‐doped samples with x=0.1–0.5 and La with x=0.05 and 0.1 appear identical to the pattern for Gd5Si4, indicating no structural change. For La ...In 1967, Holtzberg, Gambino, and McGuire (J. Phys. Chem. Solids {bold 28}, 2283 (1967)) observed that intermetallic Gd{sub 5}Si{sub 4} exhibits {ital T}{sub {ital C}} = 336 K. This is remarkable in that the {ital T}{sub {ital C}} of Gd ({similar to}291 K) is increased by chemical union with a nontransition metal, which is rare, if not unique. In the present study, magnetization-temperature behavior of Gd{sub 5}Si{sub 4} and (Gd{sub 1{minus}{ital x}}M{sub {ital x}}){sub 5}Si{sub 4} systems with M=La or Y were studied and compared with the Brillouin function (BF) to see if molecular-field theory is obeyed. Demagnetization near {ital T}{sub {ital C}} is much sharper for the alloys than expected from the BF. As examples, at {ital T}/{ital T}{sub {ital C}} = 0.9, the BF for Gd{sub 5}Si{sub 4} gives {ital M}/{ital M}{sub 0} = 0.38, whereas the observed values range from 0.99 (for (Gd{sub 0.8}Y{sub 0.2}){sub 5}Si{sub 4}) to 0.5 (for (Gd{sub 0.6}La{sub 0.4}){sub 5}Si{sub 4}). The factors responsible for these strong deviations from the BF and the high-{ital T}{sub {ital C}} values of these alloys are as yet unclear. X-ray patterns for yttrium-doped samples with {ital x}=0.1--0.5 and La with {ital x}=0.05 and 0.1 appear identical tomorexa0» the pattern for Gd{sub 5}Si{sub 4}, indicating no structural change. For La substitution of {ital x}=0.2 and above, there is a change from orthorhombic to tetragonal structure. All of the compounds show a decrease in Curie temperature and magnetic moment as Gd is decreased, as expected because of the replacement of Gd by a nonmagnetic species.«xa0less

Magnetic and structural properties of Fe/sub 3/GeN/sub x/

Magnetic and structural properties of Fe/sub 3/GeN/sub x/ have been investigated. The FCC (face centered cubic) phase of FeGe absorbs nitrogen to x=0.24. As a result of absorption, the Curie temperature and room temperature magnetization decrease from 736 K and 137 emu/g to 614 K and 74 emu/g, respectively. The HCP (hexagonal close packed) phase of Fe/sub 3/Ge, however, transforms to either FCC tetragonal phase, or a combination of these upon nitrogenation. The tetragonal nitride phase forms at a reaction temperature of 600 degrees C to 650 degrees C in a flowing atmosphere of ammonia. The phase is paramagnetic at room temperature and appears to order antiferromagnetically below 100 K. >

Auger spectroscopy of high energy magnets and some inferences regarding the mechanism of coercive force

Abstract Four laboratory-synthesized magnets, two Ndue5f8Feue5f8B and two SmCo5, have been examined by Auger spectroscopy to identify impurity phases present and to study the interfacial characteristics of the grains which comprise the sintered magnets. The Ndue5f8Feue5f8B magnets are quite heterogeneous. The intergranular regions contain particles of a secondary phase for which nFe/nNd = 1.0 ± 0.2, as well as a mixture of Nd and B oxides. The Auger results indicated an iron-depleted near-boundary layer in the grains which comprise Ndue5f8Feue5f8B magnets. This non-magnetic layer insulates one grain from its neighbors. The Auger results thus support the often-proposed notion that the high coercivity originates with some type of magnetic insulator which isolates the Nd2Fe14B grains and makes the magnets behave as an assemblage of magnetically non-interacting particles. The SmCo5 magnets were more homogeneous than the Ndue5f8Feue5f8B magnets, and their surfaces are somewhat Co-enriched relative to the bulk. This enrichment may be due to the loss of volatile Sm during processing of the sintered magnets.

Synthesis of high energy magnet materials: Coercivity mechanism, surface studies and new alloys

Abstract To date, in spite of extensive studies, only five high energy permanent magnet materials have been discovered. Hence there is an ongoing search for new materials. One, SmTi(Fe, Co)11, is promising. One characteristic required of a material is high uniaxial magnetic anisotropy. This is supplied by the rare earth crystal field interaction. This interaction is now understood well enough to have predictive value. A new use of Auger spectroscopy has revealed that the grains in Nd-Fe-B magnets are covered by a neodymium-rich film about 30–50 A thick. This iron-deficient layer is proposed to be of crucial value for high coercivity. High energy magnets are in widespread use but mostly in high technology applications. Cheaper magnets are needed for normal uses, e.g. household appliances. Lowering cost and obtaining higher flux materials are the greatest technological challenges. Understanding coercivity is the greatest scientific challenge.