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Register a new userThermal Behavior of a Single Magnetic Vortex Studied with Magnetotransport
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Spin textures such as skyrmions and magnetic vortices are good candidates for a variety of applications, such as magnetic memories, oscillators and neuromorphic computing. Understanding the magnetic process of these systems is important, as it determines the systems response in field and frequency. In this work, we investigated the magnetization process of single microdisks by measuring their magnetotransport properties as a function of temperature. The strong dependence of resistance on the disks magnetic state helped us understand the magnetization configurations of a single microdisk for different temperatures and fields. We determined the thermal barriers for the nucleation and annihilation processes by fitting the nucleation and annihilation fields to an exponential model. Moreover, we observed and characterized the domain wall depinning effect for temperatures below 100 K. This effect prevents the formation of a magnetic vortex during the nucleation process.
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Graphene on hexagonal boron-nitride (h-BN) is an atomically flat conducting system that is ideally suited for probing the effect of Zeeman splitting on electron transport. We demonstrate by magneto-transport measurements that a parallel magnetic field up to 30 Tesla does not affect the transport properties of graphene on h-BN even at charge neutrality where such an effect is expected to be maximal. The only magnetoresistance detected at low carrier concentrations is shown to be associated with a small perpendicular component of the field which cannot be fully eliminated in the experiment. Despite the high mobility of charge carries at low temperatures, we argue that the effects of Zeeman splitting are fully masked by electrostatic potential fluctuations at charge neutrality.
We have studied Josephson tunneling through a circularly polarized micron or submicron-size disk of a soft ferromagnetic material. Such a disk contains a vortex that exhibits rich classical dynamics and has recently been proposed as a tool to study quantum dynamics of the nanoscale vortex core. The change in the Josephson current that is related to a tiny displacement of the vortex core has been computed analytically and plotted numerically for permalloy disks used in experiments. It is shown that a Josephson junction with a magnetic disk in the vortex state can be an interesting physical system that may be used to measure the nanoscale motion of the magnetic vortex.
Classical transport properties of an electron, moving in plain, in an array of magnetic antidot has been calculated. The homogeneous magnetic field in z-direction fills the whole space except of cylinders of radius r_0. The magnetoresistance shows additional peak and minimum according to pinned orbits at antidots and to propagating orbits in transport direction, respectively.
We report on the switching of the magnetic vortex core in a Pac-man disk using a magnetic field pulse, investigated via micromagnetic simulations. The minimum core switching field is reduced by 72 % compared to that of a circular disk with the same diameter and thickness. However, the core switches irregularly with respect to both the field pulse amplitude and duration. This irregularity is induced by magnetization oscillations which arise due to excitation of the spin waves when the core annihilates. We show that the core switching can be controlled with the assist magnetic field and by changing the waveform.
We report on combined measurements of heat and charge transport through a single-electron transistor. The device acts as a heat switch actuated by the voltage applied on the gate. The Wiedemann-Franz law for the ratio of heat and charge conductances is found to be systematically violated away from the charge degeneracy points. The observed deviation agrees well with the theoretical expectation. With large temperature drop between the source and drain, the heat current away from degeneracy deviates from the standard quadratic dependence in the two temperatures.
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