We have performed magnetotransport measurements on La 2/3 Sr 1/3 MnO3 / SrTiO3 / La 2/3 Sr 1/3 MnO3 magnetic tunnel junctions. A magnetoresistance ratio of more than 1800 % is obtained at 4K, from which we infer an electrode spin polarization of at least 95 %. This result strongly underscores the half-metallic nature of mixed-valence manganites and demonstrates its capability as a spin analyzer. The magnetoresistance extends up to temperatures of more than 270K. We argue that these improvements over most previous works may result from optimizing the patterning process for oxide heterostructures.PACS numbers: 73.40Rw, 71.20.Eh Magnetic tunnel junctions (MTJ) have been studied actively from the mid 90's [1] due to both the underlying physics and their potential applications as magnetic memories (MRAMs) or sensors. These structures consist of two ferromagnetic metallic electrodes (FM) sandwiching a thin insulating barrier (I). When a bias voltage V DC is applied, electrons near the FM/I interface tunnel through the barrier and, since they are spin-polarized, the resistance depends on the relative orientation of the electrodes' magnetization. The tunneling magnetoresistance (TMR) ratio is defined aswhere R AP and R P are the resistances of the junction in the antiparallel and parallel configurations, respectively. In Julliere's model [2], the TMR ratio is related to the spin polarizations P 1 and P 2 of the two ferromagnetic electrodes as:Within this simple model, large TMR ratios result from electrodes, or from electrode-barrier interfaces [3], with large effective spin polarization values. Junctions which integrate amorphous barriers such as Al 2 O 3 and transition ferromagnets, for which the spin polarization does not exceed around 50 % [1, 4], do not show TMR ratios larger than 60 %. Preliminary work has been reported[5] on obtaining large interfacial spin polarizations owing to band structure effects, but the simplest route to achieving large TMR ratios relies on the use of so-called "half-metals" with a nearly total intrinsic spin polarization.A regarding their half-metallicity. Indeed, whereas spinpolarized photoemission spectroscopy experiments [10] have confirmed the half-metallic character of LSMO, the maximum spin polarization as inferred from tunneling experiments does not exceed 86% in LCMO [11] and 83% in LSMO [12].In this letter, we report a TMR ratio of more than 1800 % at T=4.2K and V DC =1mV in La 2/3 Sr 1/3 MnO 3 / SrTiO 3 / La 2/3 Sr 1/3 MnO 3 fully epitaxial MTJs, from which we deduce a spin polarization of at least 95 % for LSMO. This result confirms for the first time the transport half-metallic nature [13] of this material, which can therefore be used as a spin analyzer in tunneling experiments [3]. We argue that this large TMR value arises both from preserving the quality of the LSMO / STO (STO : SrTiO 3 ) interfaces during our upgraded patterning process, and from designing junctions of small size. The TMR extends to temperatures of about 280K, an improvement compared to previous resul...
Spin-based electronics has evolved into a major field of research that broadly encompasses different classes of materials, magnetic systems, and devices. This review describes recent advances in spintronics that have the potential to impact key areas of information technology and microelectronics. We identify four main axes of research: nonvolatile memories, magnetic sensors, microwave devices, and beyond-CMOS logic. We discuss state-of-the-art developments in these areas as well as opportunities and challenges that will have to be met, both at the device and system level, in order to integrate novel spintronic functionalities and materials in mainstream microelectronic platforms.Conventional information processing and communication devices work by controlling the flow of electric charges in integrated circuits. Such circuits are based on nonmagnetic semiconductors, in Technologies based on GMR and MTJ devices are now firmly established and compatible with CMOS fab processes. Yet, in order to meet the increasing demand for high-speed, high-density, and low power electronic components, the design of materials, processes, and spintronic circuits needs to be continuously innovated. Further, recent breakthroughs in basic research brought forward novel phenomena that allow for the generation and interconversion of charge, spin, heat, and optical signals.Many of these phenomena are based on non-equilibrium spin-orbit interaction effects, such as the spin Hall and Rashba-Edelstein effects 6,8,23 or their thermal 24 and optical 25,26 analogues. Spin-orbit torques (SOT), for example, can excite any type of magnetic materials, ranging from metals to semiconductors and insulators, in both ferromagnetic and antiferromagnetic configurations 6 . This versatility allows for the switching of single layer ferromagnets, ferrimagnets, and antiferromagnets, as well as for the excitation of spin waves and auto-oscillations in both planar and vertical device geometries 10,11 . Charge-spin conversion effects open novel pathways for information processing using Boolean logic, as well as promising avenues for implementing unconventional neuromorphic 27,28,29 and probabilistic 30 computing schemes. Finally, spintronic devices cover a broad bandwidth ranging from DC to THz 31,32 , leading to exciting opportunities for the on-chip generation and detection of high frequency signals.
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