Fe3+ Doping Effects On The Structure And Multiferroicity Of Fe1+Xv2-Xo4 (0 <= X <= 0.4) Spinels

We studied the evolution of the structural, electric, magnetic, and multiferroic properties with x in Fe1+xV2-xO4 (0 <= x <= 0.4) spinels. For x 0, three successive phase transitions occur from high to low temperatures: cubic-tetragonal (c < a) at T-S, tetragonal (c < a) paramagnetic-orthorhombic ferrimagnetic at T-N1, and orthorhombic collinear spin-tetragonal (c > a) noncollinear spin at T-N2. Below T-N2, magnetic field dependent ferroelectricity was observed. With increasing x from 0 to 0.3, T-N1 was increased, while T-S and T-N2 was decreased with ferroelectricity weakened. For x = 0.4, T-N2 together with ferroelectricity disappeared. The critical composition x(c) is around 0.3. Below xc, the resistivity follows the variable range hopping model, while above xc, the resistivity obeys nearest neighbor hooping model. Our observations evidence the strong couplings among the lattice, charge, orbital, and spin degrees of freedom as well as their effects on the structural, electric, magnetic and multiferroic properties in Fe1+xV2-xO4 spinels. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4730767]