Giant magnetoelastic response in MnAs

MnAs has been prepared from elemental powders using a modified ball-milling technique, followed by hot pressing and subsequent annealing. Giant magnet ic field-induced uniaxial strains of up to 0.7% were observed in a temperat ure range above the Curie temperature (T-C = 305 K). Dilatometric and magne tization measurements showed that the strains were associated with the volu me change accompanying a field-induced magnetostructural paramagnetic to fe rromagnetic transition above T-C. The occurrence of a tricritical point (TC P) in temperature-field space, where the two low temperature phases and the high temperature NiAs-type phase are identical was shown to be responsible for the decrease of the magnitude of both the maximum strain and magnetiza tion change with increasing temperature while approaching the TCP along the line of the first-order transitions. The coordinates of the TCP are approx imately T-tr = 405 K and H-tr = 165 kOe. (C) 1999 American Institute of Phy sics. [S0021-8979(99)04711-8].