The Spin-MOSFET is expected to show a high performance in integrated circuits (1). Efficient spin injection into semiconductors from ferromagnet is important for the realization of the Spin-MOSFET. However, it is difficult to realize efficient spin injection due to the conduction mismatch problem (2). To enhance the efficiency of spin injection, ferromagnets with high spin polarization and semiconductor like resistivity were proposed. We focused on a new class material with both these properties: Spin gapless semiconductor CoFeMnSi (CFMS). CFMS have a spin gapless structure and semiconductor behavior which have been proofed in theories and experiments (3, 4).
In this study, we aim to investigate the crystal structure, magnetic and electrical properties of CMFS thin films grown on MgO substrates.
A structure of CFMS (50nm)/Ta (5nm) was deposited by magnetron sputtering on MgO (100) substrates. The annealing temperature (Ta) of CFMS layer was between 300 and 600oC. The composition of CFMS thin films was confirmed by ICP-MS (Co : Fe : Mn : Si = 25.5 : 24.2 : 26.3 : 23.9). X-ray diffraction (XRD) was performed for characterization of crystal structure. Fig. 1 shows the annealing temperature dependence of (111) peaks of CFMS thin films. The (111) peaks were obtained above Ta = 400oC, indicating that the epitaxial growth of highly ordered (L21 or Y-type) CMFS thin films was successful. Fig. 2 shows the temperature dependence of resistivity and conductivity of CFMS thin film at Ta = 500oC. Although the electrical conductivity σxx value of our sample is around 5.3×103 S/cm, about two orders of magnitude lower than the half metallic ferromagnetic alloy Co2MnSi (~105 S/cm), non-semiconductor behaviour of resistivity was observed above 50K. Composition dependence of the CFMS thin films properties and guideline for realization of spingapless semiconductor behaviour will be presented in the conferenece.
This research was conducted by participating in the GP-Spin and JST’s SPRING program, Tohoku University, and supported by CSIS Organization for Advanced Studies and the CSRN.
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