A phenomenological model of two Co adatoms on a Cu(100) substrate was developed using a multiscale approach with “Magneto-displacement” effects taken into account. The phenomenological model used parameters obtained from density functional theory (DFT) calculations. The coupled Landau-Lifshitz equation and Newton’s equation of motion governing magnetic and mechanical degrees of freedom provide the foundation of the model. The model led to several key results. A mechanism for ferromagnetic (FM) to antiferromagnetic (AFM) transition induced by displacement of the adatoms was demonstrated. Mechanical tunability of magnetic resonant frequencies was shown. Displacement-assisted in-plane (IP) to out-of-plane (OOP) switching was demonstrated. Mechanical displacement reduces the external field needed to induce an antiferromagnetic IP to ferromagnetic OOP transition from 64T to 3T.

Hybrid multiferroic films are fabricated by depositing of Pt/Co/Pt multilayers onto [001] and [110] cuts of PMN-PT crystal. The dependence of the interfacial Dzyaloshinskii-Moriya interaction (iDMI) on applied electric field is experimentally investigated in the system by the Brilloin light scattering method. A strong variation (from -0.2 to 0.8 mJ/m2) of the iDMI constant is observed when the electric field is applied. In the case of [001] cut, the observed changes in the iDMI have an isotropic character, while in the case of [110] cut they are anisotropic, which corresponds to the symmetry of the PMN-PT deformations. The change in the iDMI is accompanied by the formation of various unusual domain structures and skyrmion lattices. External control of the DMI with an electric field opens the way to manipulate topological magnetic solitons (such as skyrmions), which are promising objects for information processing and storage.

Opening the blood brain barrier (BBB) under imaging guidance may be useful for the treatment of many brain disorders. Rapidly applied magnetic fields have the potential to generate electric fields in brain tissue that, if properly timed, may enable safe and effective BBB opening. By tuning magnetic pulses generated by a novel electropermanent magnet (EPM) array, we demonstrate the opening of tight junctions in a BBB model culture in vitro, and show that induced monophasic electrical pulses are more effective than biphasic ones. We confirmed, with in vivo contrast-enhanced MRI, that the BBB can be opened with monophasic pulses. As electropermanent magnets have demonstrated efficacy at tuning B0 fields for magnetic resonance imaging studies, our results suggest the possibility of implementing an EPM-based hybrid theragnostic device that could both image the brain and enhance drug transport across the BBB in a single sitting.

We consider magnetic oxide/heavy metal oxide hybrid film on top of a substrate with high dielectric constant. We use the double exchange model to describe the system behavior. The interface between two oxide films produces Rashba spin-orbit interaction. The phase separation appears in such a magnetic film. Combination of the phase separation and spin-orbit coupling leads to formation of electrically charged magnetic clusters with skyrmions. We show that such clusters have both electrical and topological charges. Importantly, clusters with sizes suitable for skyrmions formation may occur only for substrate with a high dielectric constant.

ABSTRACT: We study skyrmion control in an artificial ultrathin magnetic film with perpendicular anisotropy. We simulate numerically the skyrmion motion induced by spatial gradient of the Dzyaloshinskii-Moriya interaction (DMI) strength. We show that creating the DMI gradient is an efficient way to move skyrmions. In particular, experimentally achievable DMI gradients can be as effective as spin-polarized electric currents with 1011 A/m2 density. At that, the DMI gradient induces a much weaker skyrmion Hall effect. The DMI gradient can be created with a mechanical strain in a ferroelectric-ferromagnetic hybrid system. This opens an alternative way to manipulate skyrmions.

The influence of the anisotropic interfacial Dzyaloshinskii-Moriya interaction (iDMI) on the structure of magnetic domains in thin Co/Pt films is investigated using magnetic force microscopy. The iDMI anisotropy is induced via application of strong (0.08%) in-plane uniaxial mechanical strain. We observe transformation of an isotropic labyrinth domain structure to oriented stripe domains and zigzag domain structures. According to theoretical considerations, such a transformation appears due to strain-induced strong iDMI anisotropy and change of iDMI sign along the direction perpendicular to the deformation axis.

In this work, we demonstrate an experimental realization of a granular multiferroic composite, where the magnetic state of a nanocrystal array is modified by tuning the interparticle exchange coupling using an applied electric field. Previous theoretical models of a granular multiferroic composite predicted a unique magnetoelectric coupling mechanism, in which the magnetic spins of the ensemble are governed by interparticle exchange. The extent of these exchange interactions can be controlled by varying the local dielectric environment between grains. We specifically utilize the strong dielectric dependence of ferroelectric materials to modify the interparticle coupling of closely spaced magnetic nanoparticles using either a change in temperature or an electric field. This coupling modifies the ensemble magnetic coercivity and thus the superparamagnetic-to-ferromagnetic phase transition temperature. Through the use of two different ferroelectrics, our results suggest that this magnetoelectric coupling mechanism could be generalized as a new class of multiferroic material, applicable to a broad range of ferroelectric/magnetic nanocrystal composites.

We study electron transport in composite ferroelectrics — materials consisting of metallic grains embedded in a ferroelectric matrix. Due to its complex tunable morphology the thermodynamic properties of these materials can be essentially different from bulk or thin-film ferroelectrics. We calculate the conductivity of composite ferroelectrics by taking into account the interplay between charge localization, multiple grain boundaries, strong Coulomb repulsion, and ferroelectric order parameter. We show that the ferroelectricity plays a crucial role on the temperature behavior of the conductivity in the vicinity of the ferroelectric-paraelectric transition. Introduction. – Great efforts in contemporary materials science research focus on properties of composite materials. The interest is motivated by the promise to create materials with unique electrical [1,2], magnetic [3,4], thermoelectric [5], optical [6–8] and elastic [9] properties. The ease of adjusting the electronic structure of composite materials is one of their most attractive assets for fundamental studies of disordered solids and for targeted applications in nanotechnology [10]. Possible applications range from tunable capacitors to ferroelectric tunnel junctions showing giant electroresistance switching effects. Composite materials are described as solids consisting of normal metallic [11], superconducting [12–14], or ferromagnetic grains [15, 16] embedded into a dielectric matrix. In this paper we study the electron transport in composite materials consisting of metallic grains embedded into a ferroelectric (FE) matrix in the vicinity of the phase transition. Such materials attract much attention since their possible application in microelectronic devices, for example, in memory cells [17,18]. A high dielectric permittivity makes these materials prominent candidates for capacitor applications [19,20]. From the point of view of these applications, the study of the electron transport in composite ferroelectrics is a fundamentally important issue. Transport properties of materials with electric order parameter are well studied and the conductivity of ferroelectric semiconductors is well known [21]. In the vicinity of the paraelectric-ferroelectric phase transition, ferroelectric semiconductor conductivity behaves peculiarly due to variations in the ferroelectric semiconductor bandgap and electron scattering by order parameter fluctuations. In contrast to the situation of ferroelectric semiconductors, we study the case where the conductivity of the ferroelectric matrix is negligible: there are no electrons in the conduction band and all current carriers are localized in the metallic grains. In this situation electron cotunneling and variable range hopping is the only transport mechanism. Electron tunneling transport properties through single FE barrier are also studied [22–26], showing the electroresistance effect. However, coherent multi-grain processes were not studied before. Therefore, much less is known about electron transport in granular ferroelectrics, when one has to take into account the complex interplay of Coulomb interaction, ferroelectric ordering, and many grain boundaries in disordered networks of FE barriers. This defines an urgent quest for a quantitative description of properties of composite FEs. We note, that granular ferroelectrics were experimentally studied in Refs. [27, 28]. In particular, in Ref. [28] the results for the metal-insulator transition in granular ferroelectric are shown. However, most of the published data was obtained in the metallic regime, but the insulating regime is not well characterize yet. Here we investigate

We present an analytical study of domain-wall internal structure and orientation in a ferromagnetic film with out-of-plane anisotropy and the anisotropic interfacial Dzyaloshinskii-Moriya interaction (iDMI). The term "anisotropic" means that the iDMI constant is different for different in-plane directions. The interplay between the magnetostatic interaction and the iDMI in a domain wall defines both its structure and orientation. In the case of the isotropic iDMI there is no preferable orientation of the DW in the film plane leading to formation of labyrinth domain structure with random shapes of the domains. In the case of the anisotropic iDMI an oriented domain stripe structure and zigzag domains appear. Depending on system parameters, either the Bloch domain walls, or the Ne ' el ones or the hybrid canted walls realize in the magnetic film. The spatial orientation of the DW and the orientation of the magnetization rotation plane in the DW are intimately related by a simple linear ratio. The analytical results are corroborated by micromagnetic simulations.

We consider localized topologically nontrivial magnetic textures (skyrmions, antiskyrmions, and bimerons) in a thin magnetic film with anisotropic interfacial Dzyaloshinskii-Moriya interaction (iDMI). We use micromagnetic simulations and analytical consideration for studying the internal magnetic structure and stability of these textures. Skyrmion and antiskyrmion become elliptic and orient along the main axes of the iDMI tensor even for small anisotropy. In contrast, bimeron (antibimeron) orientation changes fluently with varying the iDMI anisotropy. Depending on the iDMI anisotropy the bimeron may consist of a vortex and antivortex pair or of "hedgehog" state and antivortex. In experiment the considered iDMI anisotropy can be induced by a strain applied to a magnetic film. We develop a phenomenological approach to establish the strain-iDMI relation.

The application of force in surgical settings is typically accomplished via physical tethers to the surgical tool. While physical tethers are common and critical, some internal surgical procedures may benefit from a tetherless operation of needles, possibly reducing the number of ports in the patient or the amount of tissue damage caused by tools used to manipulate needles. Magnetic field gradients can dynamically apply kinetic forces to magnetizable objects free of such tethers, possibly enabling ultra-minimally invasive robotic surgical procedures. We demonstrate the untethered manipulation of a suture needle in vitro, exemplified by steering through narrow holes, as well as needle penetration through excised rat and human tissues. We present proof of principle manipulations for the fully untethered control of a minimally modified, standard stainless steel surgical suture needle.

Interfacial Dzyaloshinskii-Moriya interaction (DMI) is experimentally investigated in Pt/Co/Pt multilayer films under strain. A strong variation (from 0.1 to 0.8  mJ/m^{2}) of the DMI constant is demonstrated at ±0.1% in-plane uniaxial deformation of the films. The anisotropic strain induces strong DMI anisotropy. The DMI constant perpendicular to the strain direction changes sign, while the constant along the strain direction does not. Estimates show that the DMI can be controlled with an electric field in hybrid ferroelectric-ferromagnetic systems. So, the observed effect opens the way to control the DMI and eventually skyrmions with a voltage via a strain-mediated magnetoelectric coupling.

The striction magnetoelectric effect in hybrid systems consisting of a magnetic film applied on the surface of a ferroelectric has been investigated. Films with planar (galfenol, nickel) and perpendicular (Co/Pt multilayer structures) magnetic anisotropy have been used. A PMN–PT crystal has served as ferroelectric. The hysteresis loops of magnetic films have been studied as a function of voltage applied to the ferroelectric crystal. A voltage applied to films with easy-plane anisotropy causes the anisotropy axis to turn in the plane of the sample. In structures with easy-axis anisotropy, the hysteresis shape changes, which, according to numerical simulation, may be associated with a change in interfacial Dzyaloshinsky–Moriya interaction at the Co/Pt interface.

Goal: To develop a micron-scale device that can operate as an MRI-based reporter for the presence of SARS-CoV-2 virus. Methods: Iron rod microdevices were constructed via template-guided synthesis and suspended in phosphate buffered saline (PBS). Heat-inactivated SARS-CoV-2 viruses were added to the samples and imaged with low-field MRI. Results: MRI of microdevices and viruses showed decreased signal intensity at low concentrations of viruses that recovered at higher concentrations. Electron micrographs suggest that reduced MRI intensity may be due to concentration-dependent shielding of water protons from local magnetic inhomogeneities caused by the iron microdevices. Conclusions: The preliminary results presented in this letter provide justification for further studies exploring the potential diagnostic role of magnetic microdevices in assessing the presence and concentration of SARS-CoV-2 viruses.

We study magneto-electric (ME) coupling mechanisms in two systems, namely ferromagnetic (FM) particles dispersed in a liquid crystal (LC) and hybrid ferroelectric (FE)-FM grains. The ME effect may appear in these systems due to the rotation of nanoparticles under the action of electric and magnetic fields. We show that a high sensitivity to the applied electric field can be achieved in both LC/magnetic particles system and hybrid FE-FM particles. In particular, even the electric field of 10 V/m essentially influences the magnetic state of these materials for proper geometric parameters. At that magnetic state, these systems can be measured in magnetic-resonance imaging (MRI) experiments. We show that MRI contrast changes up to 10% in a weak electric field. These systems can be used as MRI contrast agents for studying electrical activity in a human body.

We study a hybrid system of a magnetic oxide thin film on a ferroelectric substrate. We show that magnetic and transport properties of the magnetic oxide film strongly depend on the dielectric constant and polarization of the ferroelectric substrate. Tuning these parameters one can induce the metal-insulator transition in the magnetic oxide film accompanied by the ferromagnetic to superparamagnetic transition. Ferroelectric properties can be tuned by varying temperature or applying an electric field.

We studied the striction magnetoelectric effect in hybrid systems consisting of a magnetic film deposited on the ferroelectric surface. Films with planar (galfenol, nickel) and perpendicular (multilayer Co / Pt structures) magnetic anisotropy were used. PMN-PT crystal was used, as a ferroelectric. The hysteresis loops of magnetic films were investigated as a function of the voltage, applied to a ferroelectric crystal. In films with “easy plane” type anisotropy, a rotation of the axis directions in the plane of the sample was detected upon application of electric voltage. In structures with an "easy axis" type anisotropy, a change in the shape of the hysteresis loop is observed, which, according to the simulation, which can be associated with a change in the Dzyaloshinsky – Morii surface interaction at the Co and Pt interface

Multilayer Co/Pt films with perpendicular magnetic anisotropy are irradiated by focused a He+ ion beam to locally reduce the anisotropy value. The irradiated spots with the diameters of 100 and 200 nm are arranged in square lattices with the periods of 200 and 300 nm. The formation of nonuniform magnetic states within the spots was observed by magnetic force microscopy methods. We use the concentric distribution of the irradiation fluence within the spot to obtain the radial modulation of the anisotropy constant. This allows us to induce magnetic skyrmions during magnetization reversal of the system. The skyrmions remained stable at zero external magnetic field at room temperature. Magnetization hysteresis loops of the samples were investigated by magnetooptical methods and the results are in good agreement with micromagnetic simulations.