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Register a new userFast Switching of Bistable Magnetic Nanowires Through Collective Spin Reversal
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The use of magnetic nanowires as memory units is made possible by the exponential divergence of the characteristic time for magnetization reversal at low temperature, but the slow relaxation makes the manipulation of the frozen magnetic states difficult. We suggest that finite-size segments can show a fast switching if collective reversal of the spins is taken into account. This mechanism gives rise at low temperatures to a scaling law for the dynamic susceptibility that has been experimentally observed for the dilute molecular chain Co(hfac)2NitPhOMe. These results suggest a possible way of engineering nanowires for fast switching of the magnetization.
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Through numerical solution of the time-dependent Schrodinger equation, we demonstrate that magnetic chains with uniaxial anisotropy support stable structures, separating ferromagnetic domains of opposite magnetization. These structures, domain walls in a quantum system, are shown to remain stable if they interact with a spin wave. We find that a domain wall transmits the longitudinal component of the spin excitations only. Our results suggests that continuous, classical spin models described by LLG equation cannot be used to describe spin wave-domain wall interaction in microscopic magnetic systems.
The interaction between a spin polarized dc electrical current and spin wave modes of a cylindrical nanowire is investigated in this report. We found that close to the critical current, the uniform mode is suppressed, while the edge mode starts to propagate into the sample. When the current exceeds the critical value, this phenomenon is even more accentuated. The edge mode becomes the uniform mode of the nanowire. The higher spin wave modes are slowly pushed away by the current until the propagating mode remains.
Two promising strategies for achieving efficient control of magnetization in future magnetic memory and non-volatile spin logic devices are spin transfer torque from spin polarized currents and voltage-controlled magnetic anisotropy (VCMA). Spin transfer torque is in widespread development as the write mechanism for next-generation magnetic memory, while VCMA offers the potential of even better energy performance due to smaller Ohmic losses. Here we introduce a 3-terminal magnetic tunnel junction (MTJ) device that combines both of these mechanisms to achieve new functionality: gate-voltage-modulated spin torque switching. This gating makes possible both more energy-efficient switching and also improved architectures for memory and logic applications, including a simple approach for making magnetic memories with a maximum-density cross-point geometry that does not require a control transistor for every MTJ.
Reproducible current hysteresis is observed in graphene with a back gate structure in a two-terminal configuration. By applying a back gate bias to tune the Fermi level, an opposite sequence of switching with the different charge carriers, holes and electrons, is found. The charging and discharging effect is proposed to explain this ambipolar bistable hysteretic switching. To confirm this hypothesis, one-level transport model simulations including charging effect are performed and the results are consistent with our experimental data. Methods of improving the ON/OFF ratio of graphene resistive switching are suggested.
The exploitation of the spin in charge-based systems is opening revolutionary opportunities for device architecture. Surprisingly, room temperature electrical transport through magnetic nanowires is still an unresolved issue. Here, we show that ferromagnetic (Co) suspended atom chains spontaneously display an electron transport of half a conductance quantum, as expected for a fully polarized conduction channel. Similar behavior has been observed for Pd (a quasi-magnetic 4d metal) and Pt (a non-magnetic 5d metal). These results suggest that the nanowire low dimensionality reinforces or induces magnetic behavior, lifting off spin degeneracy even at room temperature and zero external magnetic field.
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