Chemical pressure induced spin reorientation in the magnetic structure of Ca 3 Mn 2-x Sn x O 7 (x = 0.03, 0.05).

The effect of partially substituting Tin (Sn) at the Manganese (Mn) site of Ca 3 Mn 2 O 7 viz. Ca 3 Mn 2-x Sn x O 7 with x = 0.03 and 0.05, on its structural and magnetic properties has been investigated using synchrotron diffraction, neutron diffraction, and bulk magnetization measurements. It is observed that with a substitution of only 3 at% Sn, the minor (≈ 8%) tetragonal ( I4/mmm ) structural phase that is present in the predominantly orthorhombic ( Cmc2 1 ) undoped Ca 3 Mn 2 O 7 , completely disappears. The compounds order antiferromagnetically, the ordering temperature decreases with increasing Sn-content, and indicating a weakening of the antiferromagnetic exchange interactions. Interestingly, in the ordered state, the spin magnetic moments which were aligned along the a -axis of the unit cell in the undoped compound, are observed to have reoriented with their major components lying in the b-c plane in the Sn-doped compounds. The above influence of Sn-doping is seen to be stemming from a significant modification of the octahedral rotation and tilt mode geometry in the unit cell, that is known to be responsible for driving ferroelectricity in these compounds.