Crystal structure and phase transitions in metastable Fe-Ga based alloys at cooling, heating and isothermal annealing

FeGa alloys, also known as Galfenols, exhibit an attractive combination of magnetostrictive and mechanical properties. The puzzle of the nature of giant magnetostriction in ferromagnetic Fe alloyed by nonmagnetic Ga is under extensive discussions. The effect of the structure of FeGa alloys on their functional properties is discussed practically in all research papers and a huge difference in sample properties after quick and slow cooling is firmly stated. Surprisingly, almost in all the papers the terms quick and slow are not defined with respect to cooling rates. An obvious and huge difference between structure and properties of equilibrium and metastable FeGa alloys along with a very uncertain specification for metastable state and metastable diagram lead to the urgent necessity of understanding the role of cooling rate in formation of the alloys structure at room temperature and in sequence of phase transitions at cooling.