Magnetic, thermal, and optical properties of single-crystalline CoTa₂O₆and FeTa₂O₆and their anisotropic magnetocaloric effect

Abstract

The magnetic, thermal, and optical properties of single-crystalline CoTaO and FeTaO are reported. Optical dichroism was observed in CoTaO. Magnetic susceptibility χ(T) measurements reveal long-range antiferromagnetic order with Néel temperatures [Formula: see text] K and 8.11(5) K, respectively, and anisotropy in χ. The thermal expansion coefficients exhibit significant anisotropy and the influence of the magnetic ions and long-range order. A structural phase transition to orthorhombic occurs below T for FeTaO. Magnetic field H lowers T with its affect largest when H is directed along either [1 1 0] or [1 [Formula: see text] 0], and smallest when directed along [0 0 1]. This leads to an anisotropic magnetocaloric effect that is investigated through measurements of the specific heat and magnetization in applied magnetic field.

Resonant scattering of phonons in the quasi-one-dimensional spin-chain compounds AB2O6 ( A = Ni, Co; BPrasai1, Christian2, Neumeier3 et al. 2018Phys. Rev. B3080View full textAdd to dashboardCite

“…Dimerization is plausible in the S = 3/2 Co compounds and was assumed in modeling their susceptibilities with an Ising model. 6,8 However, the resonance energies ω 0 /k B ∼ 100 K inferred from the κ analysis are equal to or twice as large as the energy difference between the lowest and highest energies for isolated dimers (9J) for CoSb and CoTa, respectively.…”

“…The dominant exchange pathways defining their AF chains, 14 [A-O-O-A], are along the [110] and [110] directions, with their orientation rotating by 90 • between neighboring layers along the crystallographic c axis, thereby giving rise to a two-sublattice description of the magnetic structure. [5][6][7][8] Long-range ordering at T N in these compounds can be viewed as a 1D to 3D transition realized through alignment of q1D regions and further alignment of stray magnetic moments, 5,6 with differing magnetic unit cells 15 and values for T N reflecting variations in the weak inter-chain exchange coupling.…”

Signatures of low-dimensional magnetism and short-range magnetic order in Co-based trirutiles

“…The bond parameters of Co1−xMgxTa2O6 at 295 K as a function of x are presented in the last row of the table. (12) work where the specific heat below T N suggested that a large fraction of spins remained disordered 17 . The neutron powder diffraction patterns obtained for x = 0.1 and 0.7 at 5 K are presented in Fig 5 (c) and (d) respectively.…”

“…Strongly correlated magnetic behaviour with reduced dimensionality has been seen in a related trirutile tantalate, NiTa 2 O 6 10 . Experimental and theoretical support for low dimensionality and anisotropic exchange interactions parallel and perpendicular to spin chains are found in several related systems 11-15 . ing disordered even at very low temperatures below the T N (6.1 K) 17 . The value of entropy change, 4.11 J/mol-K, was estimated to be below the maximum value for S = 1/2.…”

“…Recent investigation on CoTa 2 O 6 has revealed optical dichroism in the single crystals 17 . The dichroism was attributed to the anisotropic exchange mechanism related to the M -O-O-M chains.…”