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Register a new userTemperature dependence of microwave voltage emission associated to spin-transfer induced vortex oscillation in magnetic tunnel junction
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The temperature dependence of a vortex-based nano-oscillator induced by spin transfer torque (STVO) in magnetic tunnel junctions (MTJ) is considered. We obtain emitted signals with large output power and good signal coherence. Due to the reduced non-linearities compared to the uniform magnetization case, we first observe a linear decrease of linewidth with decreasing temperature. However, this expected behavior no longer applies at lower temperature and a bottom limit of the linewidth is measured.
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We studied the response of a ferromagnet-insulator-normal metal tunnel structure under an external oscillating radio frequency (R.F.) magnetic field. The D. C. voltage across the junction is calculated and is found not to decrease despite the high resistance of the junction; instead, it is of the order of $mu V$ to $100mu V$, much larger than the experimentally observed value (100 nano-V) in the strong coupled ohmic ferromagnet-normal metal bilayers. This is consistent with recent experimental results in tunnel structures, where the voltage is larger than $mu V$s. The damping and loss of an external RF field in this structure is calculated.
Atomically thin chromium triiodide (CrI3) has recently been identified as a layered antiferromagnetic insulator, in which adjacent ferromagnetic monolayers are antiferromagnetically coupled. This unusual magnetic structure naturally comprises a series of anti-aligned spin filters which can be utilized to make spin-filter magnetic tunnel junctions with very large tunneling magnetoresistance (TMR). Here we report voltage control of TMR formed by four-layer CrI3 sandwiched by monolayer graphene contacts in a dual-gated structure. By varying the gate voltages at fixed magnetic field, the device can be switched reversibly between bistable magnetic states with the same net magnetization but drastically different resistance (by a factor of ten or more). In addition, without switching the state, the TMR can be continuously modulated between 17,000% and 57,000%, due to the combination of spin-dependent tunnel barrier with changing carrier distributions in the graphene contacts. Our work demonstrates new kinds of magnetically moderated transistor action and opens up possibilities for voltage-controlled van der Waals spintronic devices.
The spin transfer torque (STT) can lead to steady precession of magnetization without any external applied field in magnetic spin valve where the magnetic layer have very different spin diffusion length. This effect is associated with an unusual angular dependence of the STT, called wavy (WAD-STT), predicted in the frame of diffusive models of spin transfer. In this article, we present a complete experimental characterization of the magnetization dynamics in the presence of a WAD-STT. The results are compared to the prediction of the magnetization dynamics obtained by single domain magnetic simulations (macrospin approximation). The macrospin simulations well reproduced the main static and dynamical experimental features (phase diagram, R(I) curves, dependence of frequency with current and field) and suggest that the dynamical excitations observed experimentally are associated with a large angle out-of-plane precession mode. The present work validates the diffusive models of the spin transfer and underlines the role of the spin accumulation and the spin relaxation effects on the STT.
The generation of oscillations in the microwave frequency range is one of the most important applications expected from spintronics devices exploiting the spin transfer phenomenon. We report transport and microwave power measurements on specially designed nanopillars for which a non-standard angular dependence of the spin transfer torque (wavy variation) is predicted by theoretical models. We observe a new kind of current-induced dynamics that is characterized by large angle precessions in the absence of any applied field, as this is also predicted by simulation with such a wavy angular dependence of the torque. This type of non-standard nanopillars can represent an interesting way for the implementation of spin transfer oscillators since they are able to generate microwave oscillations without applied magnetic field. We also emphasize the theoretical implications of our results on the angular dependence of the torque.
We demonstrate excitation of ferromagnetic resonance in CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs) by the combined action of voltage-controlled magnetic anisotropy (VCMA) and spin transfer torque (ST). Our measurements reveal that GHz-frequency VCMA torque and ST in low-resistance MTJs have similar magnitudes, and thus that both torques are equally important for understanding high-frequency voltage-driven magnetization dynamics in MTJs. As an example, we show that VCMA can increase the sensitivity of an MTJ-based microwave signal detector to the sensitivity level of semiconductor Schottky diodes.
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