Spin reorientation, magnetization reversal, and negative thermal expansion observed inRFe0.5Cr0.5O3perovskites(R=Lu,Yb,Tm)

Three members of the perovskite family $R\mathrm{F}{\mathrm{e}}_{0.5}\mathrm{C}{\mathrm{r}}_{0.5}{\mathrm{O}}_{3}$ ($R=\mathrm{Lu},\mathrm{Yb}$, and Tm) have been synthesized and characterized. A systematic study of the crystal and magnetic structures was performed by neutron powder diffraction combined with magnetization measurements. All these compounds crystallize in a Pbnm orthorhombic unit cell and they are already antiferromagnetic at room temperature. The study of the magnetic structure vs temperature showed the occurrence of a progressive spin reorientation from ${\mathrm{\ensuremath{\Gamma}}}_{4}^{\text{TM}}$ to ${\mathrm{\ensuremath{\Gamma}}}_{2}^{\text{TM}}$ for the transition metal sublattice, and in the Tm-based sample, a long-range magnetic order of the $\mathrm{T}{\mathrm{m}}^{3+}$ sublattice was found $({\mathrm{\ensuremath{\Gamma}}}_{8}^{R})$. These results are in excellent agreement with the magnetic susceptibility measurements. No spin reorientation is observed in the Lu-based sample for which a magnetization reversal at a compensation temperature ${T}_{\mathrm{comp}}=225\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ was detected. A clear magnetostrictive effect was observed in the samples with $R=\mathrm{Yb}$ and Tm associated with a negative thermal expansion and was assigned to a magnetoelastic effect produced by repulsion between the magnetic moments of neighboring transition metal ions.