Peculiarities of magnetoelastic coupling in Ni51.5Fe21.5Ga27 single crystals

A technique referred to as mechanomagnetic spectroscopy, which combines the resonant piezoelectric composite oscillator technique with measurements of the periodic stress-induced magnetization of ferromagnetic samples has been applied to study the magnetoelastic coupling in Ni51.5Fe21.5Ga27 single crystals. The composition selected demonstrates a martensitic transformation from the high-temperature cubic phase to the tetragonal one well separated from the para-ferromagnetic transition, allowing studying the high-temperature parent phase in the ferromagnetic state. Measurements were performed at fixed temperatures and oscillatory strain amplitudes as a function of periodic polarizing field and as a function of temperature for fixed values of applied magnetic field and strain amplitude. It has been found that the reversible inverse magnetostriction changes its sign in the cubic phase for the ?1?0?0? orientation, first close to the Curie temperature and then also over a certain range of temperatures below that. This anomaly is not present for the ?1?1?1? orientation. A possible origin of these peculiarities is discussed under the localized magnetic moment assumption.