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VIDEO DOI: https://doi.org/10.48448/3wsv-r007

technical paper

MMM 2022

November 07, 2022

Minneapolis, United States

Damping constant of Co2FeAl thin film deposited by molecular beam epitaxy and tunnel magnetoresistance effect using them

Magnetic Tunnel junctions (MTJs) with Co2FeAl Heusler alloy electrode are expected to show giant TMR ratio at room temperature (RT) because of its half-metallicity. In previous work, although Co2FeAl/MgO/CoFe-MTJ showed a TMR ratio of 330% at RT 1, it is still smaller than those for MTJs with CoFeB electrodes. In order to realize a large TMR ratio at RT, it is necessary to fabricate high-quality Heusler alloy electrodes and to control the interface at the atomic level. Therefore, I focused on molecular beam epitaxy (MBE) technique, which enables the fabrication of highly ordered Heusler alloy thin films 2 and atomic level interfacial modification 3. In this work, we prepared epitaxial Co2FeAl thin films by MBE technique and characterized their magnetic properties to identify the half-metallicity of the Co2FeAl films. In addition, TMR effect in Co2FeAl/MgO/CoFe-MTJs fabricated by MBE were investigated. The films were deposited on MgO(001) substrate using MBE and sputtering methods. The stacking structure of the Co2FeAl films were Cr(20)/Co2FeAl(50)/MgO(5) (unit of nm). After the fabrication of Co2FeAl layers, the films were annealed at Ta=200~700°C. Structural and magnetic properties were measured by XRD, VSM and FMR. The stacking structure of MTJs was Cr(20)/Co2FeAl(30)/MgO(2.0)/CoFe(5)/IrMn(10)/Cr(5) (unit of nm). After the microfabrication, the MTJ devices were annealed at TMTJ=275~425°C under 1T magnetic fields. TMR effects were measured by DC 4-probe method. The Co2FeAl film with Ta=600°C showed high B2 order parameter and high magnetization. In addition, as shown in Fig.1, it showed very small damping constant α of 1.8×10-3, indicating that the film has good half-metallicity. Fig.2 shows the magnetoresistance curves of the MTJs measured at RT. A relatively large TMR ratio of 125% at TMTJ=400°C was observed and the TMR ratio can be improved by insertion of ultrathin Mg or Al into the Co2FeAl/MgO interface due to suppression of the interfacial state and oxidation. This work was supported by NEDO, JSPS, GP-Spin Program and JST SPRING, Grant Number JPMJS2114.

References 1 W. Wang, H. Sukegawa and K. Inomata, Appl. Phys. Lett. 95, 182502 (2009) 2 M. Oogane, A. P. McFadden and C. J. Palmstrøm, Appl. Phys. Lett. 112, 262407 (2018) 3 K. Himi, K. Takahashi and S. Mitani, Appl. Phys. Lett. 78, 1436 (2001)


Transcript English (automatic)

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