Electronic behaviors during martensitic transformations in all-d-metal Heusler alloys

For solid-state phase transitions, the alterations of electronic structure driven by the band Jahn-Teller effect would play an essential role in the structural phase transitions and in switching the resistivity or magnetization states for potential applications. However, this evolution of the electronic structure and electronic transport during the martensitic transformations (MT) still lacks comprehensive investigations, especially in magnetic martensitic materials studied in recent years. In this work, we report a study on the electronic behaviors during the MT in a kind of all-d-metal NiFeMnTi Heusler magnetic shape memory alloys, by combining x-ray diffraction, calorimetric, magnetic, transport measurements and calculations. Based on the magnetic MTs, the system shows large magnetocaloric effect and magnetoresistance. In the whole temperature range, the system is dominated by hole carriers in both parent and martensite phases. A sharp increase in carrier concentration is observed across the transformations. Meanwhile, the mobility of holes is depressed due to the lattice distortion. A picture of the characteristics of MTs has been proposed for general understanding and clues of the potential spintronic applications based on the magnetostructural phase transitions.