Abstract
We present a study of precessional magnetization switching in orthogonal spin-torque spin-valve devices at low temperatures. The samples consist of a spin-polarizing layer that is magnetized out-of-the film plane and an in-plane magnetized free and reference magnetic layer separated by non-magnetic metallic layers. We find coherent oscillations in the switching probability, characterized by high speed switching (~200 ps), error rates as low as 10−5 and decoherence effects at longer timescales (~1 ns). Our study, which is conducted over a wide range of parameter space (pulse amplitude and duration) with deep statistics, demonstrates that the switching dynamics are likely dominated by the action of the out-of-plane spin polarization, in contrast to in-plane spin-torque from the reference layer, as has been the case in most previous studies. Our results demonstrate that precessional spin-torque devices are well suited to a cryogenic environment, while at room temperature they have so far not exhibited coherent or reliable switching.
Highlights
Spin-transfer devices that operate at low temperature are of interest for applications that require a cryogenic memory, such as Josephson junction based logic circuits[1]
This perpendicular polarizer induces precessional magnetization dynamics, as it forces the free layer magnetization out of the film plane leading to coherent precessional motion of the magnetization about the film normal: the magnet’s hard magnetic axis[6]
Switching studies are performed with a bias field set in the center of the minor hysteresis loop of Fig. 1(b). These devices operate in a different regime than those from most previous studies, inasmuch as the out-of-plane spin polarization exceeds the in-plane spin polarization
Summary
Spin-transfer devices that operate at low temperature are of interest for applications that require a cryogenic memory, such as Josephson junction based logic circuits[1]. In one case multiple oscillations are observed, but switching probabilities never approach 100%, possibly as a result of thermal decoherence and vortex formation in the free layer[15] These experiments were conducted over a relatively limited region of the phase space of applied pulse currents and durations. We study switching in OST spin-valve based devices at T = 4 K with an experimental setup designed to minimize thermal noise at the device and increase the overall measurement throughput This enables us to test a wide range of pulse amplitudes and durations and construct detailed phase diagrams of coherent magnetization dynamics. We perform finite-temperature stochastic Landau-Lifshitz-Gilbert-Slonczewski (LLGS) simulations[16] as a basis for comparison
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