N.P. Thuy

Individual site magnetic anisotropy of the iron and cobalt ions in rare earth-iron and rare earth-cobalt intermetallic compounds

Abstract The magnetic anisotropy of iron and cobalt in their compounds with rare earth elements is analysed on the base of a model in which contributions to the anisotropy from different sites are considered. From this analysis it emerges that for any specific site, the iron and cobalt contributions have different signs and differ in magnitude by almost one order of magnitude.

Magnetic anisotropy of the Y(Co1-xFex)3 pseudobinary compounds

Abstract The anisotropy energy of the Y(Co 1 - x Fe x ) 3 compounds has been determined between 4.2 and 250 K. The concentration dependence of the anisotropy energy behaves anomalously in this pseudo-binary series. Upon increasing the iron content, the anisotropy energy increases up to x = 0.25, then decreases, changes sign around x = 0.45 and reaches a flat minimum at the iron-rich side. This anomaly can satisfactorily be explained in terms of the individual site anisotropy model by considering the different occupancy factors of iron and cobalt for the 3d sites.

Magnetic anisotropy of the Y2(Co1 − xFex)14B intermetallic compounds

Abstract The magnetic anisotropy of the Y 2 (Co 1- x Fe x ) 14 B compounds has been determined in the temperature range 4.2–250 K. The anomalous concentration dependence of the anisotropy energy is explained by means of a simple model of individual site anisotropy in combination with the preferential occupation of iron atoms at different 3d sites. From the analysis of the temperature dependence of the individual site anisotropy parameters it is found that the difference in the temperature dependence of the anisotropy of the iron ions at different sites is the main reason for the observed temperature anomaly of the anisotropy of Y 2 Fe 14 B.

Magnetic and anisotropy properties of the Y2Fe17−xMnx and Er2Fe17−xMnx compounds

Abstract The effects of Mn-substitutions in the Y 2 Fe 17 and Er 2 Fe 17 compounds have been studied by magnetization measurements. The magnetic moment and the magnetic anisotropy of the 3d sublattice are found to reduce upon increasing the Mn-concentration. The magnetization reorientation processes that exist in the Er 2 Fe 14 Mn 3 and Er 2 Fe 13 Mn 4 compounds are, therefore, a consequence of competing contributions of the planar anisotropy of the 3d sublattice and the axial one of the erbium partner.

Exchange interactions in amorphous Gd–Fe alloys

Abstract The strengths of the Gd–Gd, Gd–Fe and Fe–Fe exchange couplings have been estimated from ordering temperatures for the amorphous Gd–T (T=Cu, Al and Fe) systems. The obtained Gd–Gd and Gd–Fe exchange interactions always increase with increasing Gd-concentration. These results are associated to the 5d-electron density. The Fe–Fe coupling, however, was discussed in terms of the negative interactions between the Fe–Fe pairs with the closest inter-atomic spacing.

Structure and magnetic properties of thin FePt alloy films

Abstract As-deposited and annealed FePt thin films have been studied. X-ray diffraction analysis confirmed a phase transition from γ-FCC to γ1-FCT due to annealing. Magnetic measurements revealed excellent magnetic hardening and exchange spring interaction in the annealed films. The large difference observed in Hall effect measurement on the as-deposited and annealed samples can also be assigned to this exchange spring interaction.

Formation and magnetic properties of the RCo4Si compounds

Abstract We have succeeded in preparing RCo 4 Si compounds (R = Y, Nd, Pr, Sm, Gd, Tb, Dy, Ho and Er). All samples are single phase with the CaCu 5 structure as revealed by X-ray analysis. Si substitution drastically reduces the Curie temperature of the host RCo 5 compounds. In particular, we have observed a spontaneous magnetisation of 2.34 μ B /f.u. at 5 K for SmCo 4 Si, which is significantly lower than the value of 3.0 μ B /f.u. found for YCo 4 Si. Also the temperature dependence of the spontaneous magnetisation of SmCo 4 Si shows ferrimagnetic characteristics. These results suggest an antiparallel coupling of the 3d and 4f moments in SmCo 4 Si, which has so far not been observed in light-rare-earth—transition-metal compounds. The Co magnetocrystalline anisotropy and the crystalline electric field interaction of the compounds have been studied. The results suggest the distinctive role of Si substitution in modifying the magnetic properties of the host RCo 5 compounds.

Spin reorientation phenomena in Dy1-xYxFe11Ti alloys

Abstract Spin reorientation phenomena in the Dy 1− x Y x Fe 11 Ti( x = 0, 0.2, 0.4, 0.6, 0.8 and 1) compounds have been studied by ac susceptibility and magnetization measurements on bulk and magnetically aligned powder samples. The observed concentration dependence of the spin reorientation temperatures and the temperature dependence of the cone structure of this series of compounds have been analyzed on the basis of the crystal field model. A set of crystal field parameters is proposed.

Spin reorientation in Nd1−xYxFe11Ti

Abstract Spin-reorientation phenomena have been studied in Nd 1− x Y x Fe 11 Ti compounds ( x =0, 0.2, 0.4, 0.6 and 0.8). At the spin reorientation temperature, T SR , the comparing Nd and Fe anisotropy contributions are in balance. By taking the Fe anisotropy from the Y counterpart, the anisotropy of the Nd sublattice at T SR is determined experimentally. The temperature dependence of the Nd contribution to the magnetocrystalline anisotropy has been calculated by using a Hamiltonian consisting of crystal-field and exchange terms and was compared with the experimental results. A consistent set of parameters has been deduced by which the value T SR can be reproduced for the whole series of the studied compounds.

Application of the individual site anisotropy (ISA) model to the intermetallics with the ThMn12 structure

Abstract The individual site anisotropy model was applied to the Y(Fe 1− x Co x ) 11 Ti, Y(Fe 1− x Co x ) 10 Mo 2 and YFe 12− x V x compounds with the ThMn 12 structure. Based on the relation between the CaCu 5 and ThMn 12 structures, the results are discussed in comparison with those previously obtained for R(Co 1− x Fe x ) 5 and related compounds.