Study of Coercivity-enhanced Ruthenium-doped La 0.67 Sr 0.33 MnO 3 Thin Films for Pseudo Spin Valve Devices
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1074-I03-06
Study of Coercivity-enhanced Ruthenium-doped La0.67Sr0.33MnO3 Thin Films for Pseudo Spin Valve Devices Yuk Kwan Chan, Wang Fai Cheng, Hon Kit Lau, and Chi Wah Leung Department of Applied Physics, The Hong Kong Polytechnic University, Hong Kong, China, People's Republic of ABSTRACT This investigation focused on the study of La0.67Sr0.33MnO3 (LSMO) thin films with 5 atomic percent Ru-doping (LSMRO). Specifically, we fabricated epitaxial LSMO and LSMRO thin films on LaAlO3 (LAO) (001) substrates by pulsed laser deposition. Resistance- temperature measurement results showed that the Curie temperature (Tc) of LSMRO thin film deposited under an oxygen ambient pressure of 150 mTorr at 830 oC was above room temperature. Hysteresis measurements and anisotropic magnetoresistance (AMR) results confirmed that coercivity of the optimized LSMRO films, as compared with that of LSMO films, can be greatly increased at low temperatures. The study successfully demonstrated the coercivity enhancement effect of Ru-doping on LSMO thin films deposited on LAO substrates. INTRODUCTION Giant magnetoresistive effect (GMR) has attracted much attention not only because of its applications in computer storages [1] but also due to interests on theoretical analysis of spin transport across interfaces of different materials [2]. There are several fundamental structures that can exhibit GMR, of which pseudo spin valves (PSV) being one of the prevailing structures because of its simplicity in fabrication. PSV are formed by sandwiching a non-magnetic layer between two ferromagnetic layers. PSV rely on the independent switching of magnetic layers to achieve distinct magnetization states, and to demonstrate marked step-like GMR. In order to produce coercivity contrast, various schemes including variation in magnetic layer thicknesses [3], magnetostatic coupling due to shape anisotropy [4], or using magnetic materials with marked coercivity differences, [5] have been employed. Coercivity enhancement by these methods, however, is sometimes achieved at the sacrifice of control over other parameters such as layer resistances, Curie temperatures (TC) and saturation magnetization. Recently, coercivity enhancement in La1-xSrxMnO3 ((La,Sr)MO) through Ru doping was demonstrated in bulk [6] and in thin films [7]. In the undoped state, (La,Sr)MO with x close to 0.33 has low resistivity, high TC and relatively high magnetization among oxide materials. These attributes, together with its half-metallic nature, have suggested the suitability of (La,Sr)MO as ferromagnetic electrodes in oxide based PSV structure. Interestingly, Yamada et al [7] showed that the coercivity of La0.6Sr0.4MnO3, with a few percent of Ru-doping, can be tuned to much higher values at low temperatures. Most importantly, the other figures of merits of the parent manganite, such as resistivity and saturation magnetization, were maintained. In the present study, we focus on the study of Ru-doped (La,Sr)MO thin films, i.e., the issue of coercivity enhancement of (La,Sr)MO thin films.
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