Tailored Magnetic Linear Birefringence in Wedge-Shaped Co Nanocluster Assemblies

The purpose of this paper is to present an experimental method to induce strong magnetic linear birefringence in two-dimensional assemblies of Co nanoclusters grown on glass plates. Additionally, we have also correlated the magnitude and characteristics of that nonlinear magneto-optical effect with the thickness and profile of those disordered nanostructures. For those aims, we have grown Co nanocluster assemblies on amorphous substrates, by means of pulsed laser ablation in off-axis geometry. This approach enabled us to obtain magnetic media with an intended and pronounced thickness profile, i.e., wedge-shaped assembly, to investigate the orientation and behavior of surface magnetization regarding both the thickness gradient direction and in-plane magnetic field. That study was accomplished by measuring the magneto-optical effects in reflection and transmission configurations, unveiling an out-of-plane magnetization whose magnitude depends closely on the thickness gradient direction. That component, arising from a graded magnetic anisotropy along the wedged nanostructure, adds a reversal mechanism to the surface magnetization, thus being responsible for the magnetic linear birefringence in our ultrathin Co assemblies.

The positive exchange bias property with hopping switching behavior in van der Waals magnet FeGeTe

The magnetic exchange bias effect is one of the representative interlayer magnetic coupling phenomena and is widely utilized in numerous technological applications. However, its mechanism is still elusive even in a simple magnetic bilayered system because of the complex interface magnetic orders. Van der Waals layered magnetic materials may provide an essential platform for deeply understanding the detailed mechanism of the exchange bias owing to its ideal interface structure. Here we first observed the positive exchange-biased anomalous Hall effect (AHE) with a hopping switching behavior in the FeGeTe Van der Waals nano-flakes. After systemically studying the cooling field dependence properties of the exchange bias effect, we propose that the coexistence of stable and frustrated surface magnetization of the antiferromagnetic phase will modify the total interface coupling energy density between the ferromagnetic (FM) and antiferromagnetic (AFM) phases. This model could provide a consistent description for such unusual exchange bias effect based on microspin simulation.

Surface Magnetization Reversal of Wiegand Wire Measured by the Magneto-Optical Kerr Effect

The Wiegand wire is known to exhibit a unique feature of fast magnetization reversal in the magnetically soft region accompanied by a large Barkhausen jump. We clarified a significant difference between the magnetization reversals at the surface and at the entire cross section of a Wiegand wire. We conducted magnetization measurements based on the magneto-optical Kerr effect and applied conventional methods to determine the magnetization curves. The switching field of the magnetization reversal at the surface was greater than that at the initiation of a large Barkhausen jump. Our analysis suggests that the outer surface layer exhibits low coercivity.

Magnetic Microwires with Unique Combination of Magnetic Properties Suitable for Various Magnetic Sensor Applications

There is a pressing demand to improve the performance of cost-effective soft magnetic materials for use in high performance sensors and devices. Giant Magneto-impedance effect (GMI), or fast single domain wall (DW) propagation can be observed in properly processed magnetic microwires. In this paper we have identified the routes to obtain microwires with unique combination of magnetic properties allowing observation of fast and single DW propagation and GMI effect in the same microwire. By modifying the annealing conditions, we have found the appropriate regimes allowing achievement of the highest GMI ratio and the fastest DW dynamics. The observed experimental results are discussed considering the radial distribution of magnetic anisotropy and the correlation of GMI effect, and DW dynamics with bulk and surface magnetization processes. Studies of both Fe- and Co-rich microwires, using the magneto-optical Kerr effect, MOKE, provide information on the magnetic structure in the outer shell of microwires. We have demonstrated the existence of the spiral helical structure in both studied microwires. At the same time, torsion mechanical stresses induce helical bistability in the same microwires, which allow us to consider these microwires as materials suitable for sensors based on the large Barkhausen jump.

Insulator-to-conductor transition driven by the Rashba–Zeeman effect

The Rashba effect has recently attracted great attention owing to emerging physical properties associated with it. The interplay between the Rashba effect and the Zeeman effect, being produced by the exchange field, is expected to broaden the range of these properties and even result in novel phenomena. Here we predict an insulator-to-conductor transition driven by the Rashba–Zeeman effect. We first illustrate this effect using a general Hamiltonian model and show that the insulator-to-conductor transition can be triggered under certain Rashba and exchange-field strengths. Then, we exemplify this phenomenon by considering an Ag2Te/Cr2O3 heterostructure, where the electronic structure of the Ag2Te monolayer is affected across the interface by the proximity effect of the Cr2O3 antiferromagnetic layer with well-defined surface magnetization. Based on first-principles calculations, we predict that such a system can be driven into either insulating or conducting phase, depending on the surface magnetization orientation of the Cr2O3 layer. Our results enrich the Rashba–Zeeman physics and provide useful guidelines for the realization of the insulator-to-conductor transition, which may be interesting for experimental verification.

Helical surface magnetization in nanowires: the role of chirality

Nanomagnetism is nowadays expanding into three dimensions, triggered by the discovery of new magnetic spin textures that should be studied and understood.

Revisiting the magnetization of comet 67P/Churyumov-Gerasimenko

Context. The landing of the Philae probe as part of the ESA Rosetta mission made it possible to study the magnetization of comet 67P/Churyumov-Gerasimenko (67P) by combining observations from the lander and orbiter. In this work, we revisit the magnetic properties with information gained during the progression of the mission for a comprehensive understanding of the circumstances of Philae’s descent and landing. Aims. The aim is to derive a limit for any possible magnetization of the cometary material on the surface of 67P. To achieve this, the surface contacts of Philae were analyzed. Combined with a more detailed understanding of the background magnetic field, this allows us to interpret the underlying magnetic measurements in detail. Methods. We combined magnetic field observations from the ROMAP magnetometer on board Philae with observations from the RPC-MAG instrument on board the Rosetta orbiter. To facilitate this, a correlation analysis was used to correct phase shifts between the observed signals. Additionally, in-flight calibration of the ROMAP offsets was performed using information about the dynamics of Philae during flight. These corrections made it possible to use the orbiter measurements as reference for the comet-based Philae observations. We assumed a simple dipole model and used the magnetic field observations to derive an upper limit for the magnetization of the cometary material. Results. An upper limit of 0.9 nT for the observed magnetic field on the surface of 67P was derived for any contribution from surface magnetization. For homogeneously magnetized pebbles with a size of typical aggregates in the range of ~5 cm, this translates into an upper limit of ~5 × 10−5 Am2 kg−1 for the specific magnetic moment. Depending on the exact history of formation, this results in an upper limit of 4 μT for the magnitude of the magnetic field in the solar nebula during the formation of comet 67P.