Y.M. Jana

Origin of ferromagnetic ordering of Lu2V2O7 studied with crystal-field theory in the mean-field approach

The observed dc magnetic susceptibility χ of ferromagnetic (FM) pyrochlore Lu2V2O7 is simulated using a D3d crystal-field (CF) and mean-field approach and taking into the effect of spin-orbit (s.o.) coupling and anisotropic covalency overlap. The g-tensors and the exchange interactions are found to be anisotropic. 2D term of 3d1 V4+-ions is split into 5 doublets with overall splitting Δ1 ≈ 2 eV and the total splitting of the 2T2g state Δ0 ≈ 0.4 eV under combined action of octahedral CF, trigonal distortion at V-site and s.o. coupling. The splitting of the lowest doublet due to singleion spin-spin FM long-range exchange interactions causes the sharp rise of χ below Tc ∼70 K.

Crystal-field interaction in frustrated spin-glass pyrochlore Tb2Nb2O7 revisited: Estimation of exchange interaction

The experimental dc magnetic susceptibility of pyrochlore Tb2Nb2O7 between 1.8 K and 300 K are analyzed within the frame work of appropriate crystal-field theory and a mean field approximation by introducing effective anisotropic molecular field tensors, and formulating an exact relation between single-ion susceptibility tensors and site susceptibility tensors. The susceptibility is found to be highly anisotropic along local symmetry axis of tetrahedra unit with the anisotropic values of exchange interactions among Tb-spins, λ∥ = −0.085 T/μB and λ⊥ = −0.074 T/μB.

Study on the low‐temperature properties of pyrochlores Gd2Hf2O7 and Gd2Zr2O7, using crystal‐field theory

The geometrically frustrated pyrochlores Gd2Hf2O7 (GdH) and Gd2Zr2O7 (GdZ) are easy planar anisotropic systems in which considerable single‐ion crystal‐field anisotropies of D3d symmetry are found in the ground multiplet 8S7/2 due to admixture of higher Russell‐Saunders terms. The 8S7/2 splits into 4 doublets with total CF splitting 9.9 K in GdH and 9.4 K in GdZ. The magnetic specific heat Cmag follows a conventional T3 behavior in GdH and an unconventional T4.6 behavior in GdZ down to 0.4 K.

Crystal field studies of magnetic susceptibility and specific heat properties of geometrically frustrated Gd2Sn2O7

The Gd‐based pyrochlore Gd2Sn2O7 is an easy‐planar anisotropic system. The CF anisotropy has a significant effect on the magnetic specific heat Cmag of this compound in the low temperature magnetic ordering regime. The Cmag is found to drop exponentially with Cmag mag∝1/T2 exp(−Δ1/T) between 0.12 and 0.31 K with anisotropic energy gap Δ1≈1.3±0.01 K induced by single‐ion CF anisotropy.

Effect of Single‐ion Anisotropy on the Low‐Temperature Spin Properties of Frustrated Gd2Hf2O7

Considerable single‐ion crystal‐field (CF) anisotropy of easy‐plane type is found in the frustrated pyrochlore antiferromagnet Gd2Hf2O7 (GdH) in the ground multiplet 8S7/2. It arises due to admixture of higher Russell‐Saunders terms to the ground term 8S and D3d CF at Gd‐site. The 8S7/2 splits into 4 doublets with total CF splitting 9.9 K in GdH. On the basis of CF calculation and phenomenological parametrical fitting, it is shown that magnetic specific heat Cmag follows a conventional T3 behavior down to 0.39 K which may be attributable to gapless magnon excitation.