Effect of the Temperature and Magnetic Field Induced Martensitic Transformation in Bulk Fe_45Mn_26Ga_29 Alloy on Its Electronic Structure and Physical Properties

Effect of the temperature and magnetic field induced martensitic transformation (MT) on the electronic structure and some physical properties of bulk Fe_45.2Mn_25.9Ga_28.9 Heusler alloy has been investigated. According to the experimental results of DSC, magnetic and transport measurements direct and reverse martensitic transformation without external magnetic field takes place within 194 ≤ T ≤ 328 K temperature range with a hysteresis up to Δ T ≈ 100 K defined as Δ T = A_f,s - M_s,f, where A_f,s and M_s,f are the critical temperatures of direct and reverse martensitic transformation. External magnetic field of μ_0H = 5 T causes a high-temperature shift of MT temperatures. MT from parent austenite L2_1 phase to martensitic tetragonally distorted L2_1 one (i. e. to L1_0) causes significant changes in the electronic structure of alloy, a drastic increase in alloy magnetization, a decrease in the alloy resistivity, and a reversal of the sign of the temperature coefficient of resistivity from negative to positive. At the same time experimentally determined optical properties of Fe_45.6Mn_25.9Ga_28.9 Heusler alloy in austenitic and martensitic states look visually rather similar being noticeable different in microscopic nature as can be concluded from first-principle calculations. Experimentally observed changes in the physical properties of the alloy are discussed in terms of the electronic structures of an austenite and martensite phases.