Reentrant spin reorientation transition and Griffiths-like phase in antiferromagnetic TbFe${}_{0.5}$Cr${}_{0.5}$O${}_3$

Abstract

The perovskite TbFe${}_{0.5}$Cr${}_{0.5}$O${}_3$ shows two anomalies in the magnetic susceptibility at $T_N$ = 257K and $T_{SR}$ = 190K which are respectively, the antiferromagnetic and spin reorientation transition that occur in the Fe/Cr sublattice. Analysis of the magnetic susceptibility reveals signatures of Griffiths-like phase in this compound. Neutron diffraction analysis confirms that, as the temperature is reduced from 350K, a spin reorientation transition from ${\Gamma }_2$ (F${}_x$, C${}_y$, G${}_z$) to ${\Gamma }_4$ (G${}_x$, A${}_y$, F${}_z$) occurs at $T_N$ = 257K and subsequently, a second spin reorientation takes place from ${\Gamma }_4$ (G${}_x$, A${}_y$, F${}_z$) to ${\Gamma }_2$ (F${}_x$, C${}_y$, G${}_z$) at $T_{SR}$ = 190K. The ${\Gamma }_2$ (F${}_x$, C${}_y$, G${}_z$) structure is stable until 7.7K where an ordered moment of 7.74(1)${\mu }_{\mathrm{B}}$/Fe${}^{3+}$(Cr${}^{3+}$) is obtained from neutron data refinement. In addition to the long-range order of the magnetic structure, indication of diffuse magnetic scattering at 7.7K is evident, thereby lending support to the Griffiths-like phase observed in susceptibility. At 7.7K, Tb develops a ferromagnetic component along the crystallographic $a$ axis. Thermal conductivity, and spin-phonon coupling of TbFe${}_{0.5}$Cr${}_{0.5}$O${}_3$ through Raman spectroscopy are studied in the present work. An antiferromagnetic structure with ($\uparrow \downarrow \uparrow \downarrow$) arrangement of Fe/Cr spins is found in the ground state through first-principles energy calculations which supports the experimental magnetic structure at 7.7K. The spin-resolved total and partial density of states are determined showing that TbFe${}_{0.5}$Cr${}_{0.5}$O${}_3$ is insulating with a band gap of $\sim 0.12$ (2.4) eV within GGA (GGA+$U$) functionals.

11 pages, 10 figures