On-chip micromagnets generate local magnetic-field asymmetries, enabling electrical control of spin qubits via electric dipole spin resonance and their integration into circuit quantum electrodynamics (QED) architectures. Accurate prediction of spin-qubit performance requires modeling micromagnet stray fields beyond the saturated-magnet approximation, accounting for nonuniform magnetization. Here, we combine thin-film characterization of Co, Co/Ta multilayers, and CoFe films with nanoscale stray-field measurements using NV-center magnetometry in the unsaturated regime to establish a reliable micromagnetic simulation framework. We show that CoFe micromagnets generate antisymmetric fields in double quantum-dot geometries exceeding ±100 mT, owing to their high saturation magnetization and favorable magnetocrystalline anisotropy. For spin qubits coupled to microwave resonators, the predicted spin-photon coupling reaches |gs/gc | ≈ 0.5, where gc denotes the charge-photon coupling strength of the underlying charge qubit, highlighting the potential for high-fidelity operations in circuit QED architectures.

We investigate the magnetization reversal process induced by a single femtosecond laser pulse in ferromagnetic spin valves by systematically comparing reference layers composed of pure Co, Ni, and Fe. To circumvent the loss of perpendicular magnetic anisotropy associated with changes in reference layer material and thickness, we design spin valves with in plane magnetizations. While antiparallel to parallel switching is observed for all three elements, parallel to antiparallel switching occurs only with a Co reference layer and is absent with Ni and Fe. This difference is attributed to the distinct ultrafast magnetization dynamics of the reference materials. Our results support the hypothesis that parallel to antiparallel switching requires a rapid remagnetization of the reference layer, which generates a substantial negative spin current polarized opposite to the free layer magnetization an essential condition for triggering its reversal.

Transport across model junctions built by using atomic tip or lateral techniques can generate exotic quantum signatures. However, so far, a viable industrial pathway for atom-driven electronics has been lacking. Here, we demonstrate that a commercialized device platform can help to fill this nanotechnological gap. According to conducting tip atomic force microscopy, inserting C atoms into an ultrathin MgO layer generates nanotransport paths. Across microscale magnetic tunnel junctions, resonant tunneling causes large magnetoresistance peaks that we attribute to spin accumulation onto a C nanodot that the channels transport. We ascribe the concurrent presence of a spectrally localized, nonlinear current noise and a persistent memory effect to the charging of a 'gating' C nanodot, adjacent to the 'transport' C nanodot. This nanoscale dual-dot description of quantum transport across spin states within a microscale magnetic tunnel junction should stimulate further research toward maturing spintronics into a viable quantum technological track.

We report a systematic study of single-pulse all-optical switching in Co/Gd bilayers, revealing that magnetization reversal dynamics can be tuned over 3 orders of magnitude. By varying the Gd thickness or inserting a Pt spacer layer between Co and Gd, we control the angular momentum transferred from the rare-earth sublattice to the transition-metal sublattice. Our results show that when Gd is abundant and strongly coupled to Co, angular momentum is efficiently transferred during Gd demagnetization, leading to ultrafast Co reversal. Reducing the Gd thickness or introducing Pt impedes this transfer, resulting in a slow domain growth mediated reversal as observed in CoDy and CoHo alloys. So, replacing Gd with Dy or Ho rare-earth elements slows down the switching due to a reduced angular momentum transfer toward Co upon demagnetization as demonstrated in CoGdDy alloy. Our findings establish angular momentum availability and transfer pathways as key parameters governing reversal dynamics.

The low -energy electronic spin precession is measured in the molecular field of a CoAl thin film. Designed to have a low Curie temperature, the variation of the CoAl molecular field results in an electronic spin precession angle that varies with temperature. The behavior is observed for injection energies between 0.9 and 1.2 eV and the results are explained on the basis of an exchange field varying with temperature.

The manipulation of the electron spin direction at very low electron energies is demonstrated by exploiting the exchange field present within a magnetic thin film. The design of the lab-on-chip integrated magnetic tunnel transistor allows to test different magnetic materials. The variation of film thickness, exchange field strength or electron energy are shown to have an impact on the resulting spin direction of electrons crossing a ferromagnetic material. A controlled engineering of the exchange field in thin magnetic films can therefore serve as a basis of future devices enabling controlled spin manipulation. The manipulation of the electron spin direction at very low energies is a key issue to control in future integrated devices. The design of a lab-on-chip integrated magnetic tunnel transistor allows to measure the precession angle in various magnetic materials. The variation of film thickness or exchange field strength through it temperature dependence led to the control of precession angle from 700 degrees/nm down to 0 degrees/nm. image

Magnetic field measurement including a temperature compensation is essential for a magnetic field sensor. This study investigates a magnetic surface acoustic wave (MSAW) sensor in a reflective delay line configuration with two acoustic propagation paths with and without magnetic field sensitive layer. The delay in path with sensitive layer leads to magnetic field detection and the one without enables temperature measurement and thus compensation for the first path. The developed sensor is based on a ZnO/LiNbO3 Y-cut (X-direction) layered structure as Love wave platform. Love wave as a shear wave being more favorable for magnetic detection. Co-Fe-B is considered as sensitive layer to detect magnetic field changes and is deposited on the top of ZnO, but only on one of the two paths. We combined an original configuration of connected IDTs with a high electromechanical coupling coefficient (K2) mode to improve the signal amplitude. The achieved sensor exhibits a high temperature and magnetic field sensitivity of −63 ppm/°C and −781 ppm/mT, respectively. The temperature compensation method for magnetic field measurement is demonstrated using a differential measurement by subtracting the delay times obtained for the two paths with and without the sensitive layer. Finally, the sensor exhibited good repeatability at various temperatures. Moreover, the device developed allows in addition to the multisensor functionality, the radio frequency identification (RFID) which is necessary for the deployment of sensor networks.

We experimentally demonstrate single pulse toggle switching of the magnetization of GdFeCo disks with perpendicular to film plane anisotropy, which diameter ranges from 3 μm to 400 nm using 35 fs linearly polarized laser pulses. Two different magnetic states can be observed depending on the laser fluence: either a deterministic switching of the disk magnetization or a randomly oriented disk. We report that the fluence required to observe both magnetic states show a non-monotonic behavior with disk diameter and that the smallest disks require the lowest minimum fluence for achieving single pulse all-optical helicity-independent switching. Different evolution of the fluence thresholds for both phenomenon as a function of the disk size is observed and discussed.

This paper shows the feasibility and the performance of a multifunctional device based on a surface acoustic wave delay line. It combines a magnetic field detection with a temperature sensing and has also a radio frequency identification (RFID) capability. This promising device consists of a Co-Fe-B thin film as a magnetic field sensitive material over a ZnO/LiNbO 3 Y-cut (X-direction) structure, used as a platform for guided Love waves. The experimental results show high sensitivities of -774 ppm/mT and -67.7 ppm/°C for magnetic field and temperature detection, respectively. The device thus allows magnetic field measurements with the possibility of temperature compensation which make it particularly attractive for industrial applications.

An electrical current that flows across individual atoms can generate exotic quantum transport signatures in model junctions built using atomic tip or lateral techniques. So far, however, a viable industrial pathway for atom-driven devices has been lacking. Here, we demonstrate that a commercialized device platform can fill this nanotechnological gap. According to conducting tip atomic force microscopy, inserting C atoms into the MgO barrier of a magnetic tunnel junction generates nanotransport paths. Within magnetotransport experiments, this results in quantum interferences, and in Pauli spin blockade effects linked to tunneling magnetoresistance peaks that can be electrically controlled. We report an additional persistent memory effect that we attribute to the charging of a single "gating" C atom that is adjacent to a single C atom forming the microscale junction's effective nanotranport path. Local magnetometry experiments confirm the secondary role of magnetic stray fields on the C atoms. Our results show that, to exhibit atom-level properties, a device need not be nanoscaled, and position MgO tunneling spintronics as a promising platform to industrially implement quantum technologies.

Manipulating magnetic skyrmions by means of a femtosecond (fs) laser pulse has attracted great interest due to their promising applications in efficient information-storage devices with ultralow energy consumption. However, the mechanism underlying the creation of skyrmions induced by an fs laser is still lacking. As a result, a key challenge is to reveal the pathway for the massive reorientation of magnetization from trivial to nontrivial topological states. Here, we studied a series of ferrimagnetic CoHo alloys and investigated the effect of a single laser pulse on the magnetic states. Thanks to the time-resolved magneto-optical Kerr effect and imaging techniques, we demonstrate that the laser-induced phase transitions from single domains into a topological skyrmion phase are mediated by the transient inplane magnetization state, in real time and space domains, respectively. Combining experiments and micromagnetic simulations, we propose a two-step process for creating skyrmions through laser pulse irradiation: (i) the electron temperature enhancement induces a spin reorientation transition on a picosecond (ps) timescale due to the suppression of perpendicular magnetic anisotropy (PMA) and (ii) the PMA slowly restores, accompanied by out-of-plane magnetization recovery, leading to the generation of skyrmions with the help of spin fluctuations. This work provides a route to control skyrmion patterns using an fs laser, thereby establishing the foundation for further exploration of topological magnetism at ultrafast timescales.

Ballistic hot electrons, whose energy is lower than 2.5 eV, are extracted from a magnetic tunnel junction and injected into a metallic base. After passing through the base, the electrons are energy filtered by a Schottky barrier. The use of a low height Si/Cu Schottky barrier allows to disentangle the different contributions to the scattering. The hot electrons transport is interpreted as being mainly influenced by inelastic diffusion. A transport model reproduces our measurements and explains them as resulting directly from a diffusion process related to the d-band of the ferromagnetic material involved.

A one‐port surface acoustic wave (SAW) resonator based on Co40–Fe40–B20/SiO2/ZnO/quartz multilayer structure and exhibiting a dual mode, Rayleigh and Love wave modes, is investigated to achieve a multifunctional sensor measuring both temperatures and magnetic fields. The Rayleigh wave mode of the resonator is used for temperature measurement with a temperature sensitivity of −37.9 ppm/°C, and the Love wave mode is used for magnetic field measurement. Co40‐Fe40‐B20 is the magnetic sensitive layer, and quartz crystal is the piezoelectric substrate. ZnO film is also a piezoelectric but considered here in combination with SiO2 as insulating layers and serves to control impedance matching and temperature dependence of the sensor. ZnO and SiO2 thicknesses are selected to realize temperature compensation for the Love wave mode and making this mode highly sensitive to magnetic fields and insensitive to temperatures. The magnetic field sensitivities of −170.4 kHz m−1 T−1 and −621.6 kHz m−1 T−1 are obtained respectively for the fundamental and the third harmonic of the Love wave mode. The proposed structure is beneficial to design reliable hybrid SAW magnetic field and temperature sensors.

The impact of plasmonic surface lattice resonances on the magneto-optical properties and energy absorption efficiency has been studied in arrays of [Co/Gd/Pt] N multilayer nanodisks. Varying the light wavelength, the disk diameter, and the period of the array, it is demonstrated that surface lattice resonances allow all-optical single pulse switching of [Co/Gd/Pt] N nanodisk arrays with an energy 400% smaller than the energy needed to switch a continuous [Co/Gd/Pt] N film. Moreover, the magneto-optical Faraday effect is enhanced at the resonance condition by up to 5,000%. The influence of the disk diameter and array period on the amplitude, width and position of the surface lattice resonances is in qualitative agreement with theoretical calculations and opens the way to designing magnetic metasurfaces for all-optical magnetization switching applications.

The properties of a surface acoustic wave magnetic field sensor (MSAW) based on a piezoelectric /magnetoelastic heterostructure are investigated and presented. It consists of a ZnO piezoelectric layer and a magnetoelastic metallic amorphous ribbon of 1K101 Metglas, which is a Fe-Si-B alloy, as a sensitive material. The aim is to exploit the high ΔE effect, i.e. the change of elastic properties under magnetic field, in Metglas to cause a significant change in the wave velocity and thus of the frequency in SAW resonator. We first describe the design and fabrication of the MSAW resonator, which is based on a Rayleigh wave at 422 MHz. Then, we study the sensor’s resonance frequency that was determined under (a) an in-plane magnetic field in the acoustic wave propagation direction and, (b) an out-of-plane field perpendicular to the plane. The experimental results show very high sensitivities of 2793 ppm/mT and 1482 ppm/mT, respectively, in a quite thin, compact and easy to fabricate sensor. To the best of our knowledge, the out-of-plane sensitivity is the largest reported so far, and it is of great importance for practical industrial implementations.

Recent theory and experiments have showcased how to harness quantum mechanics to assemble heat/information engines with efficiencies that surpass the classical Carnot limit. So far, this has required atomic engines that are driven by cumbersome external electromagnetic sources. Here, using molecular spintronics, an implementation that is both electronic and autonomous is proposed. The spintronic quantum engine heuristically deploys several known quantum assets by having a chain of spin qubits formed by the paramagnetic Co center of phthalocyanine (Pc) molecules electronically interact with electron-spin-selecting Fe/C60 interfaces. Density functional calculations reveal that transport fluctuations across the interface can stabilize spin coherence on the Co paramagnetic centers, which host spin flip processes. Across vertical molecular nanodevices, enduring dc current generation, output power above room temperature, two quantum thermodynamical signatures of the engine's processes, and a record 89% spin polarization of current across the Fe/C60 interface are measured. It is crucially this electron spin selection that forces, through demonic feedback and control, charge current to flow against the built-in potential barrier. Further research into spintronic quantum engines, insight into the quantum information processes within spintronic technologies, and retooling the spintronic-based information technology chain, can help accelerate the transition to clean energy.

A 5 nm thick ferrimagnetic film made of amorphous rare-earth transition-metal alloys Gdx(Fe90Co10)1-x was grown by physical vapor deposition. Its magnetic properties (coercivity, perpendicular magnetic anisotropy, and compensation composition at room temperature) were investigated for various buffer and capping layers in contact with a ferrimagnetic thin film. While Gdx(Fe90Co10)1-x appears to be amorphous for all the samples, it appears that (111) textured Cu is the best material to promote perpendicular magnetization. The large compensation composition change as a function of the magnetic film interface at room temperature is analyzed in terms of polarizability of the surrounding buffer and capping materials.

Spontaneous symmetry breaking is ubiquitous in physics. Its spectroscopic signature consists in the softening of a specific mode upon approaching the transition from the high-symmetry side and its subsequent splitting into a zero-frequency Goldstone mode and a nonzero-frequency Higgs mode. Although they determine the whole system dynamics, these features are difficult to address in practice because of their vanishing coupling to most experimental probes and/or their strong interaction with other fluctuations. In this paper, we consider a periodic magnetic modulation occurring in a ferromagnetic film with perpendicular-to-plane magnetic anisotropy and observe its Goldstone and Higgs spin-wave modes at room temperature using microwave and optical techniques. This simple system constitutes a particularly convenient platform for further exploring the dynamics of symmetry breaking.