Pressure-induced decay of the Griffiths phase and accompanying exchange-bias collapse in Gd0.5Sr0.5CoO3−δ

Abstract

The effect of pressure on both ferromagnetic (FM) cluster phase and the Griffiths phase (GP) was investigated in disordered cobaltite $\mathrm{G}{\mathrm{d}}_{0.5}\mathrm{S}{\mathrm{r}}_{0.5}\mathrm{Co}{\mathrm{O}}_{3\ensuremath{-}\ensuremath{\delta}}$, exhibiting low ${T}_{\mathrm{C}}=90\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, high Griffiths temperature ${T}_{\mathrm{G}}=220\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, and the exchange bias (EB) effect, which exists exotically inside GP. It was found that applied pressure leads to a decrease of ${T}_{\mathrm{C}}$ with a coefficient of $d{T}_{\mathrm{C}}/dP=\ensuremath{-}1\phantom{\rule{0.16em}{0ex}}\mathrm{K}/\mathrm{kbar}$ and dramatically suppresses GP, resulting in a rapid decrease in ${T}_{\mathrm{G}}$ at a rate of $d{T}_{\mathrm{G}}/dP=\ensuremath{-}3.6\phantom{\rule{0.16em}{0ex}}\mathrm{K}/\mathrm{kbar}$. Similarly, the EB field does not change significantly in the FM phase but it promptly collapses with pressure in GP, e.g., the EB field decreases four times under 10 kbar at 140 K. It appears that external pressure effectively eliminates local structure deformations that are responsible for magnetically ordered clusters existing above ${T}_{\mathrm{C}}$. It is suggested that the well-known pressure-induced transition from the high-spin $\mathrm{C}{\mathrm{o}}^{3+}$ state to the low-spin state is mainly responsible for the observed decay of the Griffiths phase and simultaneous EB collapse, as well as, for a decrease in ${T}_{\mathrm{C}}$ under pressure in $\mathrm{G}{\mathrm{d}}_{0.5}\mathrm{S}{\mathrm{r}}_{0.5}\mathrm{Co}{\mathrm{O}}_{3\ensuremath{-}\ensuremath{\delta}}$.