El’ad N. Caspi

MAGNETIC PROPERTIES OF TBCO3B2 STUDIED BY NEUTRON DIFFRACTION, MAGNETIZATION, AND AC-SUSCEPTIBILITY MEASUREMENTS

Neutron-diffraction measurements on TbCo3B2, with the isotope 11B, show ferromagnetic structure below 35(2) K. Ordered magnetic moments of Tb and Co were found to be in the basal planes directed parallel to each other. The Tb ordered moment is significantly smaller than its free-ion value. The Co ordered moment is nearly zero. Ac-susceptibility and SQUID magnetometer measurements agree with the neutron results.

Local atomic volume dependence of Tb and Co magnetic moments

The individual sizes and orientations of the magnetic moments of Tb and Co in different sites were studied by neutron diffraction of Tbn+1Co3n+5B2n (n=1, 2, 3, and ∞). Total magnetic moments obtained by our neutron diffraction measurements are in agreement with the literature and our superconducting quantum interference device measurements. The local atomic volumes dependence of Tb and Co magnetic moments are discussed using the Wigner–Seitz cell construction method.

The effect of non-magnetic dilution of the Tb sublattice in TbCo3B2.

Solid solutions of Tb(1-x)Y(x)Co(3)B(2) (x=0.05, 0.1, 0.25, 0.4 and 0.5) were studied by neutron powder diffraction, x-ray diffraction, AC susceptibility and SQUID magnetization measurements. Their magnetic and crystallographic properties were deduced and examined together with those previously published for the end compounds (x=0, 1). These solid solutions have hexagonal symmetry and are paramagnetic at RT, and undergo a magnetic ordering transition of the Co sublattice, with the magnetic moments along the hexagonal axis, at T(Co)∼150(15) K, independent of Y concentration. A second magnetic ordering transition of the Tb sublattice T(Tb)≤30 K accompanied by the rotation of the magnetic moments towards the basal plane, was observed for solid solutions with Y concentration x≤0.25. This transition was also found to be accompanied by a crystallographic symmetry decrease. Unexpectedly, neutron powder diffraction showed that the magnitude of the ordered magnetic moment of the Tb ion decreases with Tb concentration.

Polarized neutron powder diffraction by anisotropic ferromagnetic structures

Polarized neutron powder diffraction technique is extended to the case of uni-axial, high anisotropy (hard) magnetic materials. The experimental considerations of this technique are discussed and an appropriate analysis is developed.