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    Thin Films of shape memory alloys for spintronic applications

    报告人: Renat Sabirianov 教授 (University of Nebraska at Omaha)

    报告时间:2017年617日(星期六)  10:00

    报告地点:知新楼 C1111

    邀请人:康仕寿 教授

    报告简介:

        Bulk shape-memory NiMnIn alloys have attracted considerable attention due to room temperature martensitic phase transition. In electronic applications, it would be extremely desirable to synthesize thin films of such materials. Thin films of Ni52Mn35-xIn11+xSi2 were fabricated by magnetron sputtering on MgO (001) single crystal substrates. Magnetization as function of temperature for Ni52Mn35In11Si2 exhibits features consistent with a magnetostructural transition (MST) from an austenitic phase to a martensitic phase like the bulk material. We observed that the martensitic transformation is externally sensitive to small changes in chemical composition and stoichiometry. It has been found that thin films of Ni52Mn35-xIn11+xSi2 with x=0 and 1 undergo a temperature-induced MST or remain in a stable austenitic phase, respectively. Comparison of magneto-optical transverse Kerr effect spectra obtained at 0.5-4.0 eV in the 35-300 K temperature intervals reveal insignificant differences between the martensitic and austenite phases. We found that the field and temperature dependencies of the transverse Kerr effect are quite different from the magnetization behavior, which is attributed to magnetic inhomogeneity across the films. To elucidate the effects of magnetostructural phase transitions on the electronic properties, we performed density functional calculations of the magneto-optical Kerr effect.1,2 We study the impact of the substrate on the martensitic phase transformation of Ni-Mn-In thin films using magnetometry density functional theory calculations. The off-stoichiometric Ni2Mn1.5In0.5 alloy has been selected as a target since the martensitic transition observed in the bulk material is very close to ambient temperature and is therefore of practical importance. Our calculation of bulk Ni2Mn1.5In0.5 alloy shows that the cubic phase is unstable against the tetragonal distortion phase and undergoes the martensitic transformation to form tetragonal martensite in ferrimagnetic (FiM) state. Ni2Mn1.5In0.5 thin films (in both cubic and tetragonal phases) on MgO (001) substrates are studied. The presence of MgO substrate changes the relative stability of ferromagnetic (FM) austenite and FiM martensite states. Our results clearly indicate the possibility of control of martensitic transition in thin films by substrate. I will discuss the possibility of resistive switching in bilayer of NiMnIn alloys on ferroelectric substrate.