Re-entrant spin reorientation transition and Griffiths-like phase in antiferromagnetic TbFe0.5Cr0.5 O3

Abstract

The perovskite TbFe0.5Cr0.5O3 shows two anomalies in its magnetic susceptibility at TN=257 K and TSR=190 K which are, respectively, the antiferromagnetic and spin-reorientation transition that occur in the Fe/Cr sublattice. Magnetic susceptibility of this compound reveals canonical signatures of a Griffiths-like phase: a negative deviation from the ideal Curie-Weiss law and in less-than-unity power-law susceptibility exponents. Neutron-diffraction data analysis confirms two spin-reorientation transitions in this compound. The first one from Γ2 (Cx, Gy, Fz) to Γ4 (Ax, Fy, Gz) occurs at TN=257 K and a second one from Γ4 (Ax, Fy, Gz) to Γ2 (Cx, Gy, Fz) at TSR=190 K in the Pnma space-group setting. The Γ2 (Cx, Gy, Fz) structure is stable down to 7.7 K, leading to an ordered moment of 3.34(1) μB/Fe3+(Cr3+). In addition to the long-range magnetic order, experimental indication of diffuse magnetism is observed in neutron-diffraction data at 7.7 K. Tb develops a ferromagnetic component along the z axis at 20 K. Thermal conductivity and spin-phonon coupling of TbFe0.5Cr0.5O3 studied through Raman spectroscopy are also presented in the paper. The magnetic anomalies at TN and TSR do not appear in the thermal conductivity of TbFe0.5Cr0.5O3, which appears to be robust up to 9 T. On the other hand, they are revealed in the temperature dependence of full-width-at-half-maximum curves derived from Raman intensities. An antiferromagnetic structure with ↑↓↑↓ arrangement of Fe/Cr spins is found as the ground state through first-principles energy calculations, supporting the experimentally determined magnetic structure at 7.7 K. The spin-resolved total and partial density of states show that TbFe0.5Cr0.5O3 is insulating with a band gap of ∼0.12 (2.4) eV within GGA (GGA+U) functionals.