[en] Using pulsed magnetic fields up to 18 T, measurements have been carried out of the magnetostriction and magnetization of polycrystalline DyFe₂ and TbFe₂ over the temperature range 4.2-300 K. In the case of TbFe₂ the magnetostriction isotherms at all temperatures show a tendency to saturate at high field levels. The total magnetostriction decreases monotonically and is roughly proportional to the cube of the reduced magnetization. An extrapolation to infinite field and zero temperature gives a value for the saturation magnetostriction of TbFe₂ of lambda sub(s) = 3.34 x 10^-3. Assuming the polycrystalline sample to be an aggregate of non-interacting, single-domain particles it is estimated that the single-crystal magnetostriction constants are lambda₁₁₁ = 4.53 x 10^-3 and lambda₁₀₀ 5.2 x 10^-3 at 16 K. For DyFe₂ the magnetostriction isotherms below 100 k are linear in magnetic field with zero remanence. In contrast to this behaviour, the magnetization in the same temperature range shows the rapid rise at low fields which is characteristic of domain-wall movement. Estimates are made of the magnetostrictive contribution to domain energy in the case when 90⁰ domain walls are present. The possibility that the discrepancy between magnetostriction and magnetization data can be explained in terms of a lack of 90⁰ domain walls is discussed, along with the alternative conclusion that lambda₁₀₀<= lambda₁₁₁ at low temperatures. (author)

[en] The singular-point detection technique, in which the second derivative of the magnetization with respect to field is examined, has been used to determine the anisotropy field Bsub(A) = (2/Msub(s)) (K₁ + 2K₂) for Sm₂Co₁₇, Er₂Co₁₇, and Tm₂Co₁₇ over the temperature range 77 - 300 K. Exrapolation of the initial part of the hard-direction magnetization curve for aligned powders enables K₁ and K₂ to be estimated. For Er₂Co₁₇ and Tm₂Co₁₇ the rare-earth (R) and cobalt sublattices are oppositely aligned, so that the onset of ordering of the R sublattice leads to a decrease in saturation magnetization as the temperature is lowered. This is in sharp contrast to the rapid increase in K₁ at low temperatures. By subtracting the corresponding Msub(s) values from that of Y₂Co₁₇ the temperature dependence of the R sublattice can be determined. It is found that K₁ is directly proportional to the cube of this quantity, indicating the dominance of the rare-earth sublattice in determining the anisotropic properties of these compounds. For Sm₂Co₁₇ the anisotropy constant varies very strongly with the reduced magnetization. (author)

[en] The basal plane anisotropy constant K⁶₆ of dysprosium has been measured over the temperature range 4.2-120 K in fields up to 15 T. The field dependence of K⁶₆ is found to be -2.5 x 10^-4Jm^-3T^-1 and the easy-direction value of K⁶₆ is 20% larger than its mean value. (Auth.)

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[en] Using the singular point detection technique measurements are made of the temperature dependence of the first and second anisotropy constants of the pseudobinary alloy series Y₂(Cosub(x)Fesub(1-x))₁₇ where x = 0.5, 0.6, 0.7, 0.8, and 0.9. The temperature range used is 4.2 to 300 K. For all temperatures the first anisotropy constant takes a maximum value at x approximately 0.7 and extrapolates to zero at x approximately 0.5 and x approximately 0.95, confirming the change from easy-axis to easy-plane at these compositions. It is shown that these changes of easy direction and the values observed for the anisotropy constants can be accounted for in terms of the preferential substitution of iron atoms on the (6c) sites of the rhombohedral Th₂Zn₁₇ structure. Using a point charge model and assuming 100% preferential occupancy of Fe for (6c) sites, it is shown that if the charge on Co is zero, a charge of approximately +0.2|e| is required on Fe atoms to give quantitative agreement with the experimental results. (author)

[en] Alloys of the composition YCo₅ and Y₅Co₁₉ were prepared by arc melting. A thermomagnetic analysis (TMA) was carried out measuring low field dynamic initial permeability as a function of temperature. Peaks in the TMA spectra occurred at the magnetic ordering temperatures of the phases present in the sample. For Co-rich alloys the Curie temperature is a linear function of composition. This function can be used to identify the composition of unknown phases from their Curie points obtained from TMA spectra. The 5:19 and other Cromer-Larson phases have been shown to form in the Y-Co system. The 1:4 and 11:49 phases, however, appear to be unstable at room temperature

[en] Magnetostriction measurements have been carried out in the cubic Laves phase compounds DyCo₂, HoCo₂ and ErCo₂ from 10 K to well above their respective Neel temperatures Tsub(N). Pulsed magnetic fields up to 15 T (150kOe) were applied. The observed magnetostrictions are very large (approximately 10^-3) being similar to those found in the RFe₂ compounds. The measurements confirm the extremely high anisotropy of these materials. At the highest fields the polycrystalline samples are still undergoing rotational magnetization processes. The expected values of the saturation magnetostriction at O K are similar in sign and magnitude to those found in the corresponding rare earth metals. This fact and the scaling of magnetostriction with rare earth sublattice magnetization indicates that the rare earth ion is the main source of the magnetostriction. The metamagnetic transition above Tsub(N) has been studied, the relation between critical field and temperature being nonlinear for HoCo₂ and ErCo₂ . The compounds are highly anisotropic above Tsub(N) and all the features indicate that the field-induced phases are likely to be ferrimagnetic. (author)

[en] In a recent publication Groessinger et al. report measurements of anisotropy fields for samples of the pseudobinary alloy series RE₂(Fe,Co)₁₇ where RE=Y, Gd and Dy. The measurements were made using the Singular Point Detection (SPD) technique. The present paper comments on the work of Groessinger et al. (Auth.)

[en] Magnetostriction and magnetisation measurements are made on a polycrystalline sample of the cubic Laves phase compound CeFe₂ in pulsed magnetic fields up to 18 T and over the temperature range 5 to 300 K. A sharp increase in magnetostriction is observed at fields of about 3 T and at temperatures below 150 K. The magnitude of the first-order change in strain increases with decreasing temperature and at 5 K it amounts to approximately 150x10^-6 which is a 200% increase in the parallel magnetostriction. The critical field for the transition decreases slowly with decreasing temperature. The corresponding change in magnetisation is of the order of 8% at 5 K. It is proposed that this transition corresponds to a first-order rotation of the magnetisation vector due to a particular combination of anisotropy constants. In particular, the effect of the eighth-order constant K₃ which also leads to a non-symmetry easy direction above 150 K, is likely to be important. (author)