Magnetic-field -induced structural changes in the electron doped manganites: CaxSm1-xMnO3 (x = 0.8, 0.85)

We studied the correlation between magnetic, electrical, structural, and magnetostriction properties of the electron doped manganites Ca$_x$Sm$_{1-x}$MnO$_3$ (x = 0.85, 0.8). The paramagnetic to antiferromagnetic transition in both the compounds while cooling is accompanied by an abrupt increase of the spontaneous volume thermal expansion ($\Delta $V/V = 0.07 % for x = 0.85 and 0.25 % for x = 0.2). The x = 0.15 exhibits multiple phase separation at 5 K: G-type, and C-type antiferromagnetic phases in orthorhombic (\QTR{it}{Pnma}) and monoclinic (\QTR{it}{P2}$_1$\QTR{it}{/m}) structures respectively. Magnetic study on x = 0.85 also suggest ferromagnetic regions possibly in $Pnma$ structure coexist with the antiferromagnetic phases. The magnetization (M = 1.2 $\mu_B$) of x = 0.85 does not reach the value expected for the complete alignment of Mn spins even at 12 T and at 12 K. Metamagnetic transitions (C-type to Ferromagnetic) in both compounds are accompanied by contraction of volumes under high magnetic fields. We suggest that a high magnetic field induces \QTR{it}{P2}$_1$\QTR{it}{/m} (high volume) to \QTR{it}{Pnma} (low volume) structural transition. This is also supported by the neutron diffraction study.