First-order nature of the spin-reorientation phase transition in SmCrO3

The ever expected canted antiferromagnetic (CAFM) $Pb\ensuremath{'}n\ensuremath{'}m:{\mathrm{\ensuremath{\Gamma}}}_{4}({\mathbit{G}}_{\mathbit{x}},{A}_{y},{F}_{Z};{F}_{Z}^{R})$ to $Pbn\ensuremath{'}m\ensuremath{'}:{\mathrm{\ensuremath{\Gamma}}}_{2}({F}_{x},{C}_{y},{\mathbit{G}}_{\mathbit{Z}};{F}_{x}^{R}, {\mathbit{C}}_{\mathbit{y}}^{\mathbit{R}})$ spin reorientation phase transition (SRPT) has only recently been confirmed through high-resolution time-of-flight neutron scattering studies by Sau et al. [Phys. Rev. B 103, 144418 (2021)]. Despite several studies on $\mathrm{SmCr}{\mathrm{O}}_{3}$, the nature of its SRPT still remains debatable. In the present study, we revisit the issue through dc $M(T)$ and ac-susceptibility, ${\ensuremath{\chi}}_{\mathrm{ac}}(T)$, measurements. Repeated cycle field-cooled-cooling and field-cooled-warming dc $M(T)$ measurements clearly expose a temperature point differentiating the regimes of continuous and discontinuous parts of the SRPT. The discontinuous part has a tiny but clear hysteresis in $M(T)$, confirming the first-order nature of the SRPT with supercooling $({T}^{*})$ and superheating $({T}^{**})$ temperatures to be $\ensuremath{\sim}33$ and $\ensuremath{\sim}36\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, respectively. The hysteresis in the $M(T)$ is strongly supported by the occurrence of hysteresis in the nondispersing peaks in ${\ensuremath{\chi}}_{\mathrm{ac}}(T)$, measured using a 3 Oe ac signal amplitude during cooling and heating under zero dc-bias. Below SRPT, the complete reversibility of $M(T)$ and ${\ensuremath{\chi}}_{\mathrm{ac}}(T)$ confirms the second-order nature of the ${\mathrm{Sm}}^{3+}$ ordering at ${T}_{\mathrm{N}2}$, which arises due to independent ${\mathrm{Sm}}^{3+}\text{\ensuremath{-}}{\mathrm{Sm}}^{3+}$ interaction. Similarly, the absence of hysteresis in $M(T)$ as well as in ${\ensuremath{\chi}}_{\mathrm{ac}}(T)$, across the paramagnetic to CAFM ${\mathrm{\ensuremath{\Gamma}}}_{4}$ phase transition, proves the second-order nature of this phase transition.