Rare-earth chromates have always been of interest due to temperature-induced magnetization reversal and spin-reorientation phase transitions (SRPTs). In orthochromates containing magnetic rare earths, the spin configuration is supposed to undergo a characteristic changeover across the SRPT followed by an independent ordering of rare-earth moments leading to polar order. However, due to the presence of nearly 14% of highly neutron-absorbing isotope ${}^{149}\mathrm{Sm}$ in natural Sm based compounds, correct magnetic structure determination of ${\mathrm{SmCrO}}_3$ through neutron diffraction measurements has been a challenge. In the present study we investigate the pre- and post-SRPT spin configurations in well characterized ${\mathrm{SmCrO}}_3$ through time of flight neutron diffraction measurements carried out in zero field at the high-resolution high-flux WISH beam line of ISIS, in the United Kingdom. Magnetization measurement shows a canted antiferromagnetic phase transition at $T_{N1}=192\mathrm{K}$, giving rise to a weak ferromagnetism, which undergoes a SRPT at 37 K. Rietveld analysis of the neutron powder diffraction data shows that below $T_{N1}=192\mathrm{K}$ the ${\mathrm{Cr}}^{3+}$ and ${\mathrm{Sm}}^{3+}$ moments order in a $P{b}^{\prime }{n}^{\prime }m$:${\mathrm{\Gamma }}_4$(${\mathit{G}}_{\mathit{x}},A_y,F_Z;F_Z^R$) spin configuration with their tiny ferromagnetic components $F_Z$ and $F_Z^R,$ giving rise to weak ferromagnetism. Below 37 K the $P{b}^{\prime }{n}^{\prime }m$:${\mathrm{\Gamma }}_4$(${\mathit{G}}_{\mathit{x}},A_y,F_Z;F_Z^R$) configuration transforms to $Pb{n}^{\prime }{m}^{\prime }:{\mathrm{\Gamma }}_2$($F_x,C_y,{\mathit{G}}_{\mathit{Z}};F_x^R,{\mathit{C}}_{\mathit{y}}^{\mathit{R}}$) as a result of continuous rotation of ${\mathrm{Cr}}^{3+}$ moments, while approaching SRPT below $T_{N1}$. At still lower temperatures the $Pb{n}^{\prime }{m}^{\prime }:{\mathrm{\Gamma }}_2$($F_x,C_y,{\mathit{G}}_{\mathit{Z}};F_x^R,{\mathit{C}}_{\mathit{y}}^{\mathit{R}}$) phase transforms to polar phases, either the $P{2}_1^{\prime }{2}_1^{\prime }{2}_1:{\mathrm{\Gamma }}_{26}$($C_x,{\mathit{G}}_{\mathit{y}},F_z;{\mathit{C}}_{\mathit{x}}^{\mathit{R}},A_y^R,F_z^R$) or the $P{n}^{\prime }a{2}_1^{\prime }:{\mathrm{\Gamma }}_{27}$($F_x,C_y,{\mathit{G}}_{\mathit{z}};F_x^R,{\mathit{C}}_{\mathit{y}}^{\mathit{R}},G_z^R$) phase, as a result of independent antiferromagnetic ordering of ${\mathrm{Sm}}^{3+}$ moments at $T_{N2}<4\mathrm{K}$ through ${\mathrm{Sm}}^{3+}\text{−}{\mathrm{Sm}}^{3+}$ direct interaction. Our result of the transformation of ${\mathrm{SmCrO}}_3$ from ${\mathrm{\Gamma }}_4$ to ${\mathrm{\Gamma }}_2$ below SRPT is in contradiction with the ${\mathrm{\Gamma }}_1$($A_x,{\mathit{G}}_{\mathit{y}},C_Z;C_z^R$) spin configuration as reported in Tripathi et al. [Phys. Rev. B 96, 174421 (2017)]. This issue has been independently settled through ground-state energy calculation using spin-dependent density functional theory confirming the ${\mathrm{\Gamma }}_2$ spin configuration to be of lower energy as compared to that of the ${\mathrm{\Gamma }}_1$. The role of magnetocrystalline anisotropy in the occurrence of SRPT has been discussed.

• Received 4 November 2020
• Revised 2 February 2021
• Accepted 16 March 2021

DOI:https://doi.org/10.1103/PhysRevB.103.144418