Thermal expansion property of anomalous magnetic alloy Fe70Al30

D0₃-type Fe₇₀Al₃₀ shows a transition from ferromagnetism to spin glass with anomalous slow spin dynamics below 170 K. Furthermore, it shows a structural transition from D0₃ to body-centered cubic (BCC) at 823 K. In this article, the relationship between the magnetic properties, thermal expansion coefficient (TEC), and crystal structure transition of D0₃-type Fe₇₀Al₃₀ is discussed. Below 170 K, TEC decreases with temperature, accompanied by a decrease in the Fe moments. In the ferromagnetic state between 170 K and the Curie temperature (T_C), TEC increases gradually with temperature. Above T_C, TEC increases rapidly. These temperature variations of TEC could be connected to the high-spin/low-spin transition and thermal spin fluctuations. During transition from D0₃ to disordered BCC at 823 K, TEC shows discontinuous behavior, similar to a first-order transformation. With further increase in temperature, TEC becomes constant. This implies that the phase transition from D0₃ to disordered BCC is accompanied by a change in spin fluctuation.