Hysteresis effects in the phase diagram of multiferroic GdMnO3 -: art. no. 100402

We present high-resolution thermal expansion alpha(T) and magnetostriction Delta L(H)/L measurements of GdMnO3, which develops an incommensurate antiferromagnetic order (ICAFM) below T(N)similar or equal to 42 K and transforms into a canted A-type antiferromagnet (cAFM) below T(c)similar or equal to 20 K. In addition, a ferroelectric polarization P parallel to a is observed below T-FE for finite magnetic fields applied along the b direction. In zero-magnetic field, we find a strongly anisotropic thermal expansion with certain, rather broad anomalous features. In finite magnetic fields, however, very strong anomalies arise at T-c for fields applied along each of the orthorhombic axes and at T-FE for fields along the b axis. Both phase transitions are of first-order type and strongly hysteretic. We observe a downbending of the ICAFM-to-cAFM phase boundary T-c(H) for low magnetic fields and our data give evidence for coexisting phases in the low-field low-temperature range.