Promising materials for spintronics : Co2MnX (X=Si, Ge, Ga, Al, Sn) Half-Metal Magnetic grown by Molecular Beam Epitaxy

Orateur : Stéphane ANDRIEU (Insitut Jean Lamour, Nancy)

Half Metal Magnets (HMM) are of great interest in the field of spintronics because of their lack of density of states at the Fermi energy for minority spin. In other words, an HMM material is a metal for majority spins and an insulator for minority spins. Such properties lead to full spin-polarization at the Fermi energy and low magnetization damping. Theoreticians evidenced that some magnetic ternary alloys belonging to the Heusler compounds family can got this HMM behavior [1]. The HMM property was thus claimed for many Heusler alloys thin layers in order to explain transport properties, despite any direct proof of the existence of the spin gap. We studied in the past NiMnSb [2] and Co2FeGe [3] compounds (predicted to be HMM) but this behavior was not confirmed by spin-resolved photoemission (SR-PES). Recently, we observed 100% spin polarization on the Co2MnSi Heusler compound using SR-PES experiments performed on CASSIOPEE beamline at SOLEIL synchrotron source [4]. But more interestingly, we also measured very low magnetic damping below 10-3 (the lowest value reported for a conducting material up to now). This peculiar behavior, predicted by theory, is of particular interest for devices where the magnetization of an electrode has to be switched to encode information (by using spin transfer torque for instance). We show in this talk that many magnetic Heusler compounds may be grown by Molecular Beam Epitaxy. We will present a new MBE set-up (called quaternary MBE) equipped with 24 sources. This MBE is coupled to a 40m long UHV tube (fig.1), equipped with many characterization tools : Auger and X-ray spectroscopies, ARPES, Spin-resolved photoemission, in situ KERR magnetometry, AFM and STM. The epitaxial growth of several Co2MnX Heusler compounds with X=Si, Ge, Ga, Al, Sn, Sb, AlxSi1-x, and GaxGe1-x will be presented.

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