C.V. Thang

Magnetocrystalline anisotropy and RCo exchange interaction in monocrystalline RCo4Al (R = Y, Gd and Ho)

We report on the magnetic properties of the RCo4Al (R; Y, Gd, Ho) monocrystalline samples. Al substitution for Co in RCo5 results in remarkable changes of the magnetic properties not only of the Co sublattice but also of the R sublattice. These changes include a decrease of the magnetocrystalline anisotropy energy of the Co sublattice, a decrease of the RCo exchange interaction and a remarkable modification of the crystal field parameters of the R sublattice. The effects of Al substitution in RCo5 are compared with those of B substitution.

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.

Magnetic properties of monocrystalline YCo4B

Abstract A study of the magnetic properties of monocrystalline YCo4B samples is reported. A novel property, i.e. a first-order magnetisation process (FOMP), has been found in a wide temperature range. Besides this FOMP, ‘FOMP-like’ processes have been observed at certain temperatures. Apart from an anomaly corresponding to a spin-reorientation transition at 155 K, the temperature dependences of the magnetisation and the AC susceptibility show other anomalies at 30 and 80 K. The magnetocrystalline anisotropy of YCo4B is discussed in terms of a competition between contributions arising from the Co ions at different crystallographic sites.

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.

Effect of Fe substitution for Co in GdCo4B compound

Abstract The effect of Fe substitution for Co at small concentrations (x ≤ 0.1) on magnetic properties of Gd(Co1-xFex)4B compounds has been studied. Upon substitution, the compensation temperature is nearly constant, the Curie temperature changes slightly whereas the magnetic anisotropy is modified significantly. The Fe-concentration dependence of the magnetic anisotropy has been analysed by means of the individual site anisotropy (ISA) model. The magnetic phase diagram of the Gd(Co1-xFex)4 compounds is discussed.

Magnetocrystalline anisotropy and exchange interaction of single-crystalline RCo4M (R: Y, Gd, Ho; M: Al, B)

Abstract The RCo 4 M compounds (R: rare earth; M: Al, B) can be obtained from RCo 5 by substituting M for Co. For the first time, large single crystalline samples of RCo 4 M (R: Y, Gd, Ho) have been grown. Some differences have been found between the effects of Al and B substitution. In particular, a first-order magnetisation process associated with the Co sublattice is reported for RCo 4 B (R: Gd, Y).

Magnetocrystalline anisotropy of Yn+1(Co1−xFex)3n+5B2n, n = 2,3

Abstract We report on a study of Y 2 (Co 1− x Fe x ) 7 B 3 and Y 3 (Co 1− x Fe x ) 11 B 4 by magnetic measurements and Mossbauer spectroscopy. Fe substitution results in a drastic change of the magnetocrystalline anisotropy of the 3d sublattice. This effect is discussed in the framework of the individual site anisotropy (ISA) model.

Effects of Al substitution on intersublattice-exchange interaction in GdCo5-xAlx

Abstract The strength of the intersublattice Gd-Co exchange-coupling parameter, A GdCo , and the magnetic moment of the Co sublattice, M Co , are reported for the GdCo 5- x Al x ( x = 0, 0.5, 1.0, 1.5 and 1.8) compounds. As the Al content increases, a tendency to decrease is found for both A GdCo and M Co . In comparison with a previous study of Gd-Co-B series, a systematic influence of 3d-p hybridization on the 4f-3d exchange coupling is evident. These results are discussed in terms of the magnetic valence model.

Magnetic properties of monocrystalline GdCo4B

Abstract A study of the magnetic properties of monocrystalline GdCo 4 B samples is reported. A novel property, a first-order magnetisation process (FOMP), has been found in a wide temperature range. Compared to YCo 4 B, an additional positive contribution to the overall anisotropy is present in GdCo 4 B. This contribution is likely to be associated with the Gd sublattice.

Fe substitution effects on the magnetic properties of the RCo4-xFexAl compounds (R Ho and Y)

Abstract Fe substitution for Co leads to the increase of the Curie temperatures of both HoCo 4− x Fe x Al and YCo 4− x Fe x Al and of the spin-reorientation temperature of HoCo 4− x Fe x Al. In contrary, the anisotropy field of YCo 4− x Fe x Al decreases quickly with increasing Fe content. The results are explained in terms of the individual site anisotropy model.