Development of magnetic order in the TbNi(Al,In) series and magnetocrystalline anisotropy in TbTXcompounds

Abstract

We report on the magnetic structures in the TbNiAl 1−x In x compounds as determined by powder neutron diffraction. These compounds belong to a large family of ternary rare-earth intermetallics crystallizing in the ZrNiAl-type hexagonal structure. All studied compounds order magnetically with magnetic structures characterized by k 1 = (0,0,0) and k 2 = ( 1 2 ,0, 1 2 ) propagation vectors and magnetic moments aligned along or perpendicular to the hexagonal c axis. The magnetocrystalline anisotropy changes from uniaxial in the In-poor compounds (x 0.4) to planar in the In-rich compounds (x 0.5). The change of magnetocrystalline anisotropy type is a consequence of the development of structural parameters in the studied series. The Tb moments are oriented along the c axis when the nearest Tb-Tb distances between the planes are large compared to those within the planes, whereas Tb moments lie within the basal planes in the opposite case. This picture relating the structural parameters and anisotropy type can be generalized to the whole group of Tb-based compounds with the ZrNiAl type of structure.

Pressure Influence on Magnetic Properties of TbNiAl

“…By applying the hydrostatic pressure, both lattice parameters decrease, the volume decreases and c/a ratio decreases as well due to higher compressibility along the c axis [7]. The values of c and c/a thus show the same trend as for the InAl substitution in the TbNi(Al,In) series [5], whereas the a parameter shows the opposite trend. As the eect on magnetic properties is opposite strengthening the antiferromagnetic ground state, one can draw a hypothesis that mainly the TbTb distances within the basal plane, which are related to the a parameter and represent the shortest TbTb distance, aect the nature of the magnetic ground state in TbNiAl.…”

“…Previous results indicated that TbNiAl is a rare example of a localized system in which the magnetic properties seem to be very sensitive to structural changes caused by substitutions [5]. One can expect that similar eects can be thus achieved by applying external pressure.…”