X-ray structural and magnetic studies of the magnetic-martensitic transition in Gd$_5$Si$_{0.5}$Ge$_{3.5}$

Intermetallic Gd$_5$Si$_{0.5}$Ge$_{3.5}$ undergoes a martensitic phase transition between two different orthorhombic polymorphs. This transition, which involves large shear displacements of atoms, expands the unit cell volume on warming and causes the dissapearance of ferromagnetic ordering. We report Gd $L_3$ and Ge $K$- edges XMCD and XAFS measurements on this compound as a function of temperature and magnetic field. The results indicate this transition appears to occur through an intermediate phase. This phase affects the magnetic ordering and can be transformed into the low temperature martensitic phase by the application of a magnetic field.