Dynamics of the magnetic field-induced first order magnetic-structural phase transformation of Gd5(Si0.5Ge0.5)4

The system Gd-5(SixGe1-x)(4) for 0.4less than or equal toxless than or equal to0.5 has been shown to have an unusual first order, coupled magnetic-structural phase transformation at the Curie temperature. Above the transformation temperature T-c, the material is paramagnetic with a monoclinic structure; below T-c, it is ferromagnetic with an orthorhombic structure. Another unusual feature of this phase transformation is that an applied magnetic field can increase T-c by 5 K per tesla. In this study, the magnetic-structural transformation in single crystal Gd5Si2Ge2 was triggered by holding the sample at a temperature just above T-c, then using an applied field to increase T-c beyond the sample temperature, thereby inducing the magnetic-structural transformation. The dynamics of this field-induced phase transformation at various temperatures just above T-c were observed by measuring the magnetization as a function of time. This magnetization change is caused by the first order phase transformation which is distinctly different from the magnetization reversal which one observes in conventional magnetic relaxation experiments. The transformation could be modeled as a thermal activation process with a single energy barrier of height 4.2+/-0.2 eV. (C) 2004 American Institute of Physics.