Spin reorientation and magnetic structure of HoCo12B6 ferrimagnetic compound.

The magnetic phase diagram is determined by combining magnetization measurements, ac susceptibility and neutron diffraction. The crystal and magnetic structures are also investigated. The HoCo12B6 compound exhibits ferrimagnetic behavior below TC = 147 K. Two antiferromagnetically coupled sublattices cancel out at the compensation temperature TComp = 46 K. HoCo12B6 undergoes a spin reorientation transition at TSR = 76 K; the easy magnetization axis changes from axial to basal plane upon heating. The magnitude of the magnetic moments and their orientation are described and discussed. It is revealed that HoCo12B6 compound exhibits a commensurate magnetic structure below TSR and an incommensurate one slightly above TSR. Significantly different magnetic moments have been observed on the two Co crystal sites, a very low magnetic moment of 0.14 µB being refined on the Co 18 g position. In addition, the second order crystal electric-field parameter A2(0) at the rare-earth site is determined. This result is discussed and used to explain the observed spin reorientation transition by a competition between the Co and Ho sublattice anisotropy.

Large magnetovolume effects due to transition from the ferromagnetic to antiferromagnetic state in Hf0.825Ta0.175Fe2 intermetallic compound.

Intrinsic magnetic properties and magnetovolume effects have been investigated for the Hf0.825Ta0.175Fe2 itinerant-electron system, which exhibits a temperature-induced first-order transition from the ferromagnetic (FM) to the antiferromagnetic (AFM) state. The spontaneous volume magnetostriction contraction due to this transition from the high-volume FM state to the low-volume AFM state is about 0.66%. Applying a magnetic field increases significantly the FM-AFM transition temperature T(FM-AFM), with a rate of 7.2 K T(-1). At temperatures T > T(FM-AFM) a first-order metamagnetic transition between the AFM and FM states has been observed from isothermal magnetization curves, a result attributed to the itinerant-electron character of the Fe magnetism. This AFM-FM transition is accompanied by a huge field-induced volume magnetostriction. The change in ΔV/V due to the AFM-FM transition is about 0.75%.

Ferrimagnetism in GdCo(12-x)Fe(x)B6.

The effects of iron substitution on the structural and magnetic properties of the GdCo(12-x)Fe(x)B6 (0 ≤ x ≤ 3) series of compounds have been studied. All of the compounds form in the rhombohedral SrNi12B6-type structure and exhibit ferrimagnetic behaviour below room temperature: T(C) decreases from 158 K for x = 0 to 93 K for x = 3. (155)Gd Mössbauer spectroscopy indicates that the easy magnetization axis changes from axial to basal-plane upon substitution of Fe for Co. This observation has been confirmed using neutron powder diffraction. The axial to basal-plane transition is remarkably sensitive to the Fe content and comparison with earlier (57)Fe-doping studies suggests that the boundary lies below x = 0.1.