Fast magnetization reversal of a magnetic nanoparticle induced by cosine chirp microwave field pulse

We investigate the magnetization reversal of single-domain magnetic nanoparticle driven by the circularly polarized cosine chirp microwave pulse (CCMP). The numerical findings, based on the Landau-Lifshitz-Gilbert equation, reveal that the CCMP is by itself capable of driving fast and energy-efficient magnetization reversal. The microwave field amplitude and initial frequency required by a CCMP are much smaller than that of the linear down-chirp microwave pulse. This is achieved as the frequency change of the CCMP closely matches the frequency change of the magnetization precession which leads to an efficient stimulated microwave energy absorption (emission) by (from) the magnetic particle before (after) it crosses over the energy barrier. We further find that the enhancement of easy-plane shape anisotropy significantly reduces the required microwave amplitude and the initial frequency of CCMP. We also find that there is an optimal Gilbert damping for fast magnetization reversal. These findings may provide a pathway to realize the fast and low-cost memory device.

Orientational characteristics of magnetization precession excitation on the interference grating formed by femtosecond laser.

The subject of investigation in this work is the excitation of magnetization precession in magnetic film on the surface of which is formed the temperature relief which is formed by interference picture formatted by preliminary divided ray from femtosecond laser. It is mentioned the discovered in experiment the dependence of excitation efficiency from the orientation of magnetic field applied in the plane of film. The main aim of this work is the theoretical interpretation of observed orientation dependence. The realized in experiment scheme “pump-probe” is described. The whole geometry of task is proposed. This geometry includes in oneself the magnetic film with formed in its surface interference picture and applied in the plane of film the constant field. It is shown that by the thermal expansion in the film the elastic waves two types are excited; the surface Rayleigh waves and leaky longitudinal waves. The projections of wave-vectors of propagating waves to plane of film are normal to the strips of interference picture. The orientation of field may change from to longitudinal to transverse from the same strips. The components of deformation tensor of Rayleigh and leaky waves are determined. The precession of magnetization in the coordinate system connected with field is investigated. By using the apparatus of crossing matrixes it is found the components of deformation tensor are determined. In the frame of linear approach in this system the task about excitation of magnetization precession by elastic deformations by Rayleigh and leaky waves is solved. The dynamical component of magnetization precession which ensures the light polarization rotation which passes along the normal to the plane of film is found. It is shown that the angle of rotation is straight proportional to the tensor deformation components with the summarization with the resonance character of precession magnetization dependence from the value of magnetic field. The dependence of polarization rotation from orientation of field which is applied in the plane of film is found. It is shown that by the orientation of field along and across the interference stripes the rotation of polarization plane is absent. Between these extreme orientations the dependence has appearance as two maxima divided by deep minimum. The received results are compared with data of experiment. It is found the quality and in some cases quantity correlation. The recommendations for further development of work are proposed.

Ultrastrong photon-to-magnon coupling in multilayered heterostructures involving superconducting coherence via ferromagnetic layers

The critical step for future quantum industry demands realization of efficient information exchange between different-platform hybrid systems that can harvest advantages of distinct platforms. The major restraining factor for the progress in certain hybrids is weak coupling strength between the elemental particles. In particular, this restriction impedes a promising field of hybrid magnonics. In this work, we propose an approach for realization of on-chip hybrid magnonic systems with unprecedentedly strong coupling parameters. The approach is based on multilayered microstructures containing superconducting, insulating, and ferromagnetic layers with modified photon phase velocities and magnon eigenfrequencies. The enhanced coupling strength is provided by the radically reduced photon mode volume. Study of the microscopic mechanism of the photon-to-magnon coupling evidences formation of the long-range superconducting coherence via thick strong ferromagnetic layers in superconductor/ferromagnet/superconductor trilayer in the presence of magnetization precession. This discovery offers new opportunities in microwave superconducting spintronics for quantum technologies.

Quantum paradigm of the foldover magnetic resonance

The explosive development of quantum magnonics requires the consideration of several previously known effects from a new angle. In particular, taking into account the quantum behavior of magnons is essential at high excitations of the magnetic system, under the conditions of the so-called phenomenon of “foldover” (bi-stable) magnetic resonance. Previously, this effect was considered in the quasi-classical macrospin approximation. However, at large angles of magnetization precession, the magnon density exceeds the critical value for the formation of a magnon Bose condensate (mBEC). Naturally, this purely quantum phenomenon does not exist in the classical approximation. In addition, mBEC leads to superfluid transfer of magnetization, which suppresses the macroinhomogeneity of the samples. The experiments presented in the article show that quantum phenomena well describes the experimental results of nonlinear magnetic resonance in yttrium iron garnet. Thus, we remove the questions that arose earlier when considering this effect without taking into account quantum phenomena. This discovery paves the way for many quantum applications of supermagnonics, such as the magnetic Josephson effect, long-range spin transport, Q-bits, quantum logic, magnetic sensors, and others.

Uncooled sub-GHz spin bolometer driven by auto-oscillation

Bolometers are rectification devices that convert electromagnetic waves into direct current voltage through a temperature change. A superconducting bolometer has a responsivity of approximately 106–107 V/W under cryogenic temperatures at infrared wavelengths; however, no devices have realized such a high responsivity in the sub-GHz frequency region. We describe a spin bolometer with a responsivity of (4.40 ± 0.04) × 106 V/W in the sub-GHz region at room temperature using heat generated in magnetic tunnel junctions through auto-oscillation. We attribute the unexpectedly high responsivity to a heat-induced spin-torque. This spin-torque modulates and synchronizes the magnetization precession due to the spin-torque auto-oscillation and produces a large voltage output. In our device, heat-induced spin-torque was obtained because of a large heat-controlled magnetic anisotropy change: −2.7 µJ/Wm, which is significant for enhancing dynamic range and responsivity. This study can potentially lead to the development of highly sensitive microwave detectors in the sub-GHz region.

Controllable Magnetization Precession Dynamics and Damping Anisotropy in Co2FeAl Heusler-Alloy Films

Magnetization dynamics of the epitaxially-grown Co2FeAl (CFA) thin films have been systematically investigated by the time-resolved magneto-optical Kerr effect (TR-MOKE). The dependences of precession frequency f, relaxion time τ and...