Enhanced ferroelectricity in orthorhombic manganites Gd1-xHoxMnO3

A series of orthorhombic manganites Gd1-xHoxMnO3 (0 <= x <= 0.5) are synthesized. The Ho doping leads to a transition of paraelectric phase into ferroelectric one, making Gd1-xHoxMnO3 multiferroic. It is argued that the enhanced electric polarization originates from the transition of the A-type Mn3+ anti-ferromagnetic state into the spiral spin order driven by the reduction of Mn-O-Mn bond angle due to the doping. The noncollinear spin order of the A-site Ho3+ spins at high doping level may also make contribution to the polarization. (c) 2011 American Institute of Physics. [doi: 10.1063/1.3535543]