R.J. Radwański

Magnetic properties of ternary rare-earth compounds of the type R2Fe14B

Abstract Ternary tetragonal compounds of the composition R 2 Fe 14 B were observed for R = Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, and Lu. The lattice constants and the X-ray density of these compounds were determined. Also determined were the magnetic properties, comprising the temperature dependence of the magnetization in the range 4.2–700 K and the field dependence of the magnetization at 4.2 K in fields up to 20 T. These latter measurements were made in two mutually perpendicular directions, making it possible to determine the anisotropy fields. The magnetocrystalline anisotropy was found to consist of contributions due to the Fe and rare-earth sublattice, respectively.

Magnetic and crystallographic characteristics of rare-earth ternary carbides derived from R2Fe17 compounds

Abstract We have studied the magnetic properties of the rhombohedral R 2 Fe 17 C compounds with R = Ce, Pr, Sm, Gd, Tb, Dy, Ho or Y and the hexagonal R 2 Fe 17 C compounds with R = Er, Tm or Lu. For all compounds the lattice parameters were determined. The Curie temperatures were found to be considerably enhanced with respect to the C-free counterparts. The magnetic anisotropy of the R 2 Fe 17 C compounds was studied on magnetically aligned powders in field strengths up to 35 T. The rare-earth sublattice anisotropy is much stronger in R 2 Fe 17 C than in R 2 Fe 17 , leading to an easy c -axis anisotropy in Sm 2 Fe 17 C even at room temperature. The Curie temperatures and the high field data obtained at 4.2 K were analysed in terms of a mean field model.

Magnetic and crystallographic properties of ternary rare earth compounds of the type R2Co14B

Abstract Ternary tetragonal compounds of the composition R 2 Fe 14 C were observed for R = Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm and Lu. The lattice constants of these compounds were determined. Also determined were the magnetic properties, comprising the temperature dependence of the magnetization in the range 4.2–700 K and the field dependence of the magnetization at 4.2 K in fields up to 35 T. These latter measurements were made on magnetically-a ligned powders with the field parallel and perpendicular to the alignment direction, making it possible to determine the anisotropy fields. The magnetocrystalline anisotropy, consisting of contributions due to the Fe and rare-earth sublattice, was found to be of comparable magnitude in R 2 Fe 14 C and R 2 Fe 14 B.

Strength of the rare-earth-transition-metal exchange coupling in hard magnetic materials, an experimental approach based on high-field magnetisation measurements: Application to Er2Fe14B

Abstract A new experimental technique is presented to determine the intersublattice molecular-field coefficient, n RT , in heavy rare-earth-transition-metal intermetallic compounds. The technique is based on high-field magnetisation measurements on finely powdered polycrystalline material that is free to rotate in the sampleholder. Experimental results are reported for a number of Er 2 Fe 14− x Mn x B compounds. The strength of the RT exchange coupling is not affected by the Mn substitution, and a value of 0.445 Tkg/Am 2 has been deduced for the coefficient n RT .

Rare earth magnetocrystalline anisotropy in R2Fe14B compounds — High-field magnetization process

Abstract The high-field magnetization behavior of the R2Fe14B compounds has been studied on Ho2Fe14B as an example. It is shown that the ferrimagnetic structure is strongly disturbed by external magnetic fields and that the magnetization process proceeds by a reversible magnetic reorientation. From the high-field magnetization experiments a value of υBHex/kB=144 K has been derived for the exchange field, apart from values for the magnetocrystalline anisotropy coefficients of the holmium sublattice. A set of crystal-field parameters of the Ho3+ ion in Ho2Fe14 has been evaluated.

The specific heat of ErNi5 and LaNi5

The specific heat of ErNi5 and LaNi5 has been measured on single-crystalline specimens in the temperature interval from 1.5 K to 250 K. By comparison, the contribution of the Er subsystem to the specific heat has been determined. This contribution is well accounted for within a single-ion Hamiltonian that includes the CEF and exchange interactions of the Er3+ ions. The CEF interactions of the Er3+ ion have been compared with those found in other RNi5 compounds and the remarkable constancy of CEF interactions through the 4f series is discussed.

Magnetocrystalline anisotropy and crystal field in Ho2Co17

Abstract High-field magnetization curves of Ho 2 Co 17 are analyzed in terms of crystal- and molecular-field interactions. The magnetic moments are slightly tilted out of the hexagonal plane as a result of crystal-field (CF) interactions. A full set of CF parameters for the two non-equivalent rare-earth ions in the hexagonal structure has been evaluated reconciling Mossbauer, inelastic-neutron-scattering, specific-heat and high-magnetic-field results. Exchange interactions between the 3d and 4f spins in the Ho 2 Co 17 and Ho 2 Fe 14 B compounds are compared and discussed.

The electronic structure of the Nd3+ ion in Nd2Fe14B

Abstract The properties of the trivalent neodymium ion in the Nd 2 Fe 14 B compound have been analyzed within a single-ion Hamiltonian. Macro- and microscopic parameters of the neodymium anisotropy have been derived. The calculated energy level scheme of the neodymium ion reproduces all features of the magnetization experiments and is compared with inelastic-neutron-scattering results.

The strength of the R-T exchange coupling in R2Fe14B compounds

Abstract The R-T exchange-coupling parameter of the ferrimagnetic R 2 Fe 14 B compounds (R = Gd, Tb, Dy, Ho, Er, Tm) has been deduced from high-field magnetisation measurements at 4.2 K on finely powdered Mn-doped samples of which the powder particles are free to orient themselves in the applied magnetic field. Values ranging from 0.954×10 -22 to 1.29×10 -22 J have been derived.

Exchange interactions and basal-plane magnetocrystalline anisotropy in R2Co17 intermetallics

Abstract The transition fields that recently have been observed in the basal-plane magnetisation curves of Ho 2 Co 17 can successfully be described in a two-sublattice model and provide a direct method to evaluate the molecular field acting on the holmium moment. Its value of 63.5 T corresponds, in a molecular-field approximation, to a value of 0.924x10 -22 J for the coupling between the holmium and cobalt spins. The basal-plane magnetocrystalline anisotropy of the holmium moment is found to be 2.2x10 -22 J. On the basis of these numbers the molecular field acting on the rare-earth moment and the basal-plane anisotropy are calculated for the whole series of R 2 Co 17 compounds.