Negative exchange bias in single-phaseDy1−xNdxCrO3induced by Nd doping

Abstract

Observation of significant negative exchange bias (${H}_{E}$) is reported in solid solutions of single-phase samples of $\mathrm{D}{\mathrm{y}}_{1\ensuremath{-}x}\mathrm{N}{\mathrm{d}}_{x}\mathrm{Cr}{\mathrm{O}}_{3}$ for $x=0.33,\phantom{\rule{0.16em}{0ex}}0.67,$ and 1 with corresponding N\'eel temperatures at ${T}_{N}^{\mathrm{Cr}}=175\phantom{\rule{0.16em}{0ex}}\mathrm{K},\phantom{\rule{4pt}{0ex}}200\phantom{\rule{0.16em}{0ex}}\mathrm{K},$ and 225 K, respectively, and the spin-reorientation transitions ${T}_{SR}$ at 48 K, 58 K, and 38 K, respectively. In contrast, no ${H}_{E}$ was observed for the sample with $x=0$ (i.e., $\mathrm{DyCr}{\mathrm{O}}_{3}$) shows no ${H}_{E}$ below its ${T}_{N}^{\mathrm{Cr}}=145\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, and no reorientation of spins at lower temperatures was observed. More importantly, the (negative) ${H}_{E}$ for the $x=0.33,\phantom{\rule{0.16em}{0ex}}0.67,$ and 1 samples is observed only in the temperature range between ${T}_{N}$ and ${T}_{SR}$ with the corresponding observation of magnetic coercivity. These results show that the canted antiferromagnetic ${\mathrm{\ensuremath{\Gamma}}}_{7,\mathrm{Cr}}$ structure of the $\mathrm{C}{\mathrm{r}}^{3+}$ moments present between ${T}_{N}^{\mathrm{Cr}}$ and ${T}_{SR}$ is essential for the observed ${H}_{E}$. By comparing this result to the literature, common features of single-phase materials with ${H}_{E}$ were identified. The present bulk powder samples were prepared by the citrate method and structurally characterized by x-ray diffraction and Raman spectroscopy techniques. Neutron diffraction measurements for the $x=0.33,\phantom{\rule{0.16em}{0ex}}0.67,$ and 1 samples at select temperatures were done to verify the presence of the ${\mathrm{\ensuremath{\Gamma}}}_{7,\mathrm{Cr}}$ structure between ${T}_{N}^{\mathrm{Cr}}$ and ${T}_{SR}$ and the ${\mathrm{\ensuremath{\Gamma}}}_{1,\mathrm{Cr}}$ structure (with no canting of $\mathrm{C}{\mathrm{r}}^{3+}$ moments) below ${T}_{SR}$.