Thermal expansion of single crystal Gd/sub 5/(Si/sub 2/Ge/sub 2/) showing unusual first-order phase transformation

Summary form only given. Alloys based on rare earth with group IV elements have been intensively investigated since the Gd/sub 5/(Si/sub x/Ge/sub 1-x/)/sub 4/ system was found to have a giant magnetocaloric effect in 1997. However, the thermal expansion of this system has seldom been studied. In this paper, the thermal expansion of single crystal Gd/sub 5/(Si/sub 2/Ge/sub 2/) along the principal axis was measured in a closed cycle He-refrigerator system. The results show that there is an abrupt change in strain when the sample was cooled down or heated up through the phase transition temperature. The phase change has the character of a first order transition. It shows a hysteresis associated with the cooling and heating cycle. It is believed that this strain anomaly is due to an unusual magnetic-martensitic phase transformation in which the material is paramagnetic and has monoclinic crystal structure above the transition temperature and is ferromagnetic and has orthorhombic crystal structure below the transition temperature. An applied magnetic field was observed to shift the transition temperature. A 10kOe magnetic field applied along the a-axis direction while cooling raised the transition temperature by about 5 K.