Epitaxial L1 0 MnAl films demonstrated two different kinds of magneto-transport behaviors as a function of temperature. The magneto-resistance ratio (MR) was negative and exhibited evident enhancement in the resistivity at coercive fields above ~175 K. The MR enhancement was attributed to the increase of the magnetic domain walls based on the quantitative correlation between the domain density and the resistivity. Below 175 K, the MR was positive and showed a quadratic dependence on the external magnetic field, which implied that the MR was dominated by Lorentz effects below 175 K.
Chromium dioxide (CrO2) is a half metal that is of interest for spintronic devices. It has not been synthesized through traditional physical vapor deposition (PVD) techniques because of its thermodynamic instability in low oxygen pressures. Epitaxial thin films of Ru doped tetragonal rutile CrO2 were synthesized by a PVD technique. The as-deposited RuxCr1−xO2 was ferrimagnetic with the saturation magnetization moment showing a strong dependence on the Ru concentration. Curie temperature as high as 241 K has been obtained for ∼23 at. % Ru. The Ru substitution increased the electrical conductivity by increasing the minority spin concentration. The spin polarization was found to be as high as 70% for 9 at. % Ru and decreased to ∼60% with Ru concentrations up to ∼44 at. %, which is determined by the Fermi velocities of the majority and minority spins. First principle calculations were performed to understand the effect of Ru content on the properties of CrO2. The PVD processes of Ru doped CrO2 could lead to the practical applications of the high spin polarization of CrO2 in spintronic devices.
DC current induced magnetization reversal and magnetization oscillation was observed in 500 nm large size Co 90 Fe 10 /Cu/Ni 80 Fe 20 pillars. A perpendicular external field enhanced the coercive field separation between the reference layer (Co 90 Fe 10 ) and free layer (Ni 80 Fe 20 ) in the pseudo spin valve, allowing a large window of external magnetic field for exploring the free-layer reversal. The magnetization precession was manifested in terms of the multiple peaks on the differential resistance curves. Depending on the bias current and applied field, the regions of magnetic switching and magnetization precession on a dynamical stability diagram has been discussed in details. Micromagnetic simulations are shown to be in good agreement with experimental results and provide insight for synchronization of inhomogenieties in large sized device. The ability to manipulate spin-dynamics on large size devices could prove useful for increasing the output power of the spin-transfer nano-oscillators (STNOs).Spin-polarized currents can be harnessed to manipulate magnetization and excite oscillation via the spin transfer torque (STT) effect, and are utilized in the application of MRAM [1,2] and spin-transfer nano-oscillators (STNOs) [3,4] . STNOs have the advantages that their frequencies are highly tunable by current and magnetic field over a range from 2 a few GHz to 40 GHz. [3,5] Furthermore, the nanometer sized devices are among the smallest microwave oscillators yet developed [6] and their compatibility with standard silicon processing opens the possibility for on-chip applications. [7,8] However, the bottlenecks for the widespread application of STNOs lies in the enhancement of the output power above the current limit of ~ 0.5µW. [9] It has been suggested that two nano-contact STNOs in close proximity could mutually phase-lock and increase the output power; however phase-locking of more than two STNOs remains technologically challenge. [10][11][12][13][14] Instead of putting an array of STNOs nano-magnets together, we propose to make use of larger sized magnets in the hope that synchronization of multiple domains could lead to higher output power, and firstly we demonstrated that spin-transfer torque can be used to efficiently induce magnetization switching and oscillation in 500 nm large size devices. For large size device, our simulation results have shown that the non-uniform oscillations tend to synchronize with each other and generate coherent oscillation. In addition, large sized nano-magnets can be fabricated more cost-effectively through photolithography rather than using electron beam lithography. 3The magnetic multilayer was synthesized by sputtering in a Biased Target Ion Beam Deposition system (BTIBD). The deposition details can be found elsewhere. [15] The complete structure of the multilayer is SiO 2 (substrate)/20nm Ru/2.2nm Co 90 Fe 10 (reference layer)/5nm Cu/6.5nm Ni 80 Fe 20 (free layer)/5nm Ru/Ti 5nm/Au 25nm. A magnetoresistance (MR) of ~1.2% was measured in the pseudo spin-valve continuous f...
One of many challenges for niobium (Nb) based superconducting devices is the improvement over the surface morphology and superconducting properties as well as the reduction of defects. We employed a novel deposition technique, i.e. biased target ion beam deposition technique (BTIBD) to prepare Nb thin films with controlled crystallinity and surface morphology. We found that the target current (I Target ) and the target bias (V Target ) were critical to the crystallinity and surface morphology of Nb films. The high target current (I Target >500 mA and V Target = 400 V bias) during the deposition degraded the Nb crystallinity, and subsequently reduced the critical temperature for superconductivity (T c ). V Target was critical to the surface morphology, i.e. grain size and shape and the surface roughness. The optimized growth condition yielded very smooth film with RMS roughness of 0.4 nm that was an order of magnitude smoother than that of Nb films by sputtering process. The critical temperature for superconductivity was also close to the value of the bulk Nb. The quality of Nb film was evident in the presence of a very thin proximity layer (~ 0.8 nm). The experimental results demonstrated that the preparation of smooth Nb films with adequate superconductivity by BTIBD could serve as a base electrode for the in-situ magnetic layer or insulating layer for superconducting electronic devices.
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