Magnetostriction is the spontaneous deformation that all magnetic materials undergo with the application of a magnetic field, effectively coupling electrical energy with mechanical work. With the discovery of giant magnetostriction in Tb_{1-x}Dy_xFe_2 (Terfenol-D) 30 years ago and Fe_{1-x}Ga_x (Galfenol) more recently, the phenomenon has been utilised in actuators, sensors, sonar and commercial devices. Key to a material's applicability in these cases is the temperature dependence of its magnetic properties.

Our study presents a non-empirical computational method for calculating the magnetostriction of materials as a function of temperature. Looking at pure Fe in particular, our results show good qualitative agreement with experiment, in particular reproducing the anomalous, non-monotonic thermal behaviour of bcc Fe’s magnetostriction, which has been largely unexplained for more than 50 years. Our calculations show that thermal expansion plays an important role.

Applying the same method to the fully disordered A2 phase of Galfenol successfully reproduces the experimentally observed suppression of non-monotonic temperature dependence with increasing Ga content. However, the dramatic enhancement of magnetostriction with gallium content is not observed, indicating that it is important to consider short range ordering in this material.

Journal reference: G. A. Marchant et al., Phys. Rev. B 99, 054415 (2019)

DOI: 10.1103/PhysRevB.99.054415