Voltage controlled Néel vector rotation in zero magnetic field

Perspectives: Light Control of Magnetism and Device Development

Accurately controlling magnetic and spin states presents a significant challenge in spintronics, especially as demands for higher data storage density and increased processing speeds grow. Approaches such as light control are gradually supplanting traditional magnetic field methods. Traditionally, the modulation of magnetism was predominantly achieved through polarized light with the help of ultrafast light technologies. With the growing demand for energy efficiency and multifunctionality in spintronic devices, integrating photovoltaic materials into magnetoelectric systems has introduced more physical effects. This development suggests that sunlight will play an increasingly pivotal role in manipulating spin orientation in the future. This review introduces and concludes the influence of various light types on magnetism, exploring mechanisms such as magneto-optical (MO) effects, light-induced magnetic phase transitions, and spin photovoltaic effects. This review briefly summarizes recent advancements in the light control of magnetism, especially sunlight, and their potential applications, providing an optimistic perspective on future research directions in this area.

Fawaeer S, Holcman V. Exploring the Piezoelectric Properties of Bismuth Ferrite Thin Films Using Piezoelectric Force Microscopy: A Case Study

Over recent decades, the scientific community has managed to make great progress in the theoretical investigation and practical characterization of bismuth ferrite thin films. However, there is still much work to be completed in the field of magnetic property analysis. Under a normal operational temperature, the ferroelectric properties of bismuth ferrite could overcome the magnetic properties due to the robustness of ferroelectric alignment. Therefore, investigation of the ferroelectric domain structure is crucial for functionality of any potential devices. This paper reports deposition and analyzation of bismuth ferrite thin films by Piezoresponse Force Microscopy (PFM) and XPS methods, aiming to provide a characterization of deposited thin films. In this paper, thin films of 100 nm thick bismuth ferrite material were prepared by pulsed laser deposition on multilayer substrates Pt/Ti(TiO₂)/Si. Our main purpose for the PFM investigation in this paper is to determine which magnetic pattern will be observed on Pt/Ti/Si and Pt/TiO₂/Si multilayer substrates under certain deposition parameters by utilizing the PLD method and using samples of a deposited thickness of 100 nm. It was also important to determine how strong the measured piezoelectric response will be, considering parameters mentioned previously. By establishing a clear understanding of how prepared thin films react on various biases, we have provided a foundation for future research involving the formation of piezoelectric grains, thickness-dependent domain wall formations, and the effect of the substrate topology on the magnetic properties of bismuth ferrite films.

The spin polarization of palladium on magneto-electric Cr2O3

While induced spin polarization of a palladium (Pd) overlayer on antiferromagnetic and magneto-electric Cr₂O₃(0001) is possible because of the boundary polarization at the Cr₂O₃(0001), in the single domain state, the Pd thin film appears to be ferromagnetic on its own, likely as a result of strain. In the conduction band, we find the experimental evidence of ferromagnetic spin polarized in Pd thin films on a Cr₂O₃(0001) single crystal, especially in the thin limit, Pd thickness of around 1-4 nm. Indeed there is significant spin polarization in 10 Å thick Pd films on Cr₂O₃(0001) at 310 K, i.e. above the Néel temperature of bulk Cr₂O₃. While Cr₂O₃(0001) has surface moments that tend to align along the surface normal, for Pd on Cr₂O₃, the spin polarization contains an in-plane component. Strain in the Pd adlayer on Cr₂O₃(0001) appears correlated to the spin polarization measured in spin polarized inverse photoemission spectroscopy. Further evidence for magnetization of Pd on Cr₂O₃is provided by measurement of the exchange bias fields in Cr₂O₃/Pd(buffer)/[Co/Pd]_nexchange bias systems. The magnitude of the exchange bias field is, over a wide temperature range, virtually unaffected by the Pd thickness variation between 1 and 2 nm.

Characterizing and Overcoming Surface Paramagnetism in Magnetoelectric Antiferromagnets

We use a combination of density functional theory and Monte Carlo methods to calculate the surface magnetization in magnetoelectric Cr_{2}O_{3} at finite temperatures. Such antiferromagnets, lacking both inversion and time-reversal symmetries, are required by symmetry to possess an uncompensated magnetization density on particular surface terminations. Here, we first show that the uppermost layer of magnetic moments on the ideal (001) surface remains paramagnetic at the bulk Néel temperature, bringing the theoretical estimate of surface magnetization density in line with experiment. We demonstrate that the lower surface ordering temperature compared to bulk is a generic feature of surface magnetization when the termination reduces the effective Heisenberg coupling. We then propose two methods by which the surface magnetization in Cr_{2}O_{3} could be stabilized at higher temperatures. Specifically, we show that the effective coupling of surface magnetic ions can be drastically increased either by a different choice of surface Miller plane, or by Fe doping. Our findings provide an improved understanding of surface magnetization properties in AFMs.

Nanoscale imaging of antiferromagnetic domains in epitaxial films of Cr2O3 via scanning diamond magnetic probe microscopy

We report direct imaging of boundary magnetization associated with antiferromagnetic domains in magnetoelectric epitaxial Cr₂O₃ thin films using diamond nitrogen vacancy microscopy. We found a correlation between magnetic domain size and structural grain size which we associate with the domain formation process. We performed field cooling, i.e., cooling from above to below the Néel temperature in the presence of a magnetic field, which resulted in the selection of one of the two otherwise degenerate 180° domains. Lifting of such a degeneracy is achievable with a magnetic field alone due to the Zeeman energy of a weak parasitic magnetic moment in Cr₂O₃ films that originates from defects and the imbalance of the boundary magnetization of opposing interfaces. This boundary magnetization couples to the antiferromagnetic order parameter enabling selection of its orientation. Nanostructuring the Cr₂O₃ film with mesa structures revealed reversible edge magnetic states with the direction of magnetic field during field cooling.

Rufinamide, a Triazole-Derived Antiepileptic Drug, Stimulates Ca2+-Activated K+ Currents While Inhibiting Voltage-Gated Na+ Currents

Rufinamide (RFM) is a clinically utilized antiepileptic drug that, as a triazole derivative, has a unique structure. The extent to which this drug affects membrane ionic currents remains incompletely understood. With the aid of patch clamp technology, we investigated the effects of RFM on the amplitude, gating, and hysteresis of ionic currents from pituitary GH₃ lactotrophs. RFM increased the amplitude of Ca²⁺-activated K⁺ currents (I_K(Ca)) in pituitary GH₃ lactotrophs, and the increase was attenuated by the further addition of iberiotoxin or paxilline. The addition of RFM to the cytosolic surface of the detached patch of membrane resulted in the enhanced activity of large-conductance Ca²⁺-activated K⁺ channels (BK_Ca channels), and paxilline reversed this activity. RFM increased the strength of the hysteresis exhibited by the BK_Ca channels and induced by an inverted isosceles-triangular ramp pulse. The peak and late voltage-gated Na⁺ current (I_Na) evoked by rapid step depolarizations were differentially suppressed by RFM. The molecular docking approach suggested that RFM bound to the intracellular domain of K_Ca1.1 channels with amino acid residues, thereby functionally affecting BK_Ca channels' activity. This study is the first to present evidence that, in addition to inhibiting the I_Na, RFM effectively modifies the I_K(Ca), which suggests that it has an impact on neuronal function and excitability.

Coexistence of Magnetoelectric and Antiferroelectric-like Orders in Mn3Ta2O8

In materials showing a linear magnetoelectric (ME) effect, unconventional functionalities can be anticipated such as electric control of magnetism and nonreciprocal optical responses. Thus, the search for new linear ME materials is of interest in materials science. Here, using a recently proposed design principle of linear ME materials, which is based on the combination of local structural asymmetry and collinear antiferromagnetism, we demonstrate that an anion-deficient fluorite derivative, Mn₃Ta₂O₈, is a new linear ME material. This is evidenced by the onset of magnetic-field-induced electric polarization in its collinear antiferromagnetic phase below T_N = 24 K. Furthermore, we also find an antiferroelectric-like phase transition at T_S = 55 K, which is attributable to an off-center displacement of magnetic Mn²⁺ ions. The present study shows that Mn₃Ta₂O₈ is a rare material that exhibits both ME and antiferroelectric-like transitions. Thus, Mn₃Ta₂O₈ may provide an opportunity to investigate the physics associated with complicated interactions between magnetic (spin) and electric dipole degrees of freedom.

Voltage control of ferrimagnetic order and voltage-assisted writing of ferrimagnetic spin textures

Voltage control of magnetic order is desirable for spintronic device applications, but 180° magnetization switching is not straightforward because electric fields do not break time-reversal symmetry. Ferrimagnets are promising candidates for 180° switching owing to a multi-sublattice configuration with opposing magnetic moments of different magnitudes. In this study we used solid-state hydrogen gating to control the ferrimagnetic order in rare earth-transition metal thin films dynamically. Electric field-induced hydrogen loading/unloading in GdCo can shift the magnetic compensation temperature by more than 100 K, which enables control of the dominant magnetic sublattice. X-ray magnetic circular dichroism measurements and ab initio calculations indicate that the magnetization control originates from the weakening of antiferromagnetic exchange coupling that reduces the magnetization of Gd more than that of Co upon hydrogenation. We observed reversible, gate voltage-induced net magnetization switching and full 180° Néel vector reversal in the absence of external magnetic fields. Furthermore, we generated ferrimagnetic spin textures, such as chiral domain walls and skyrmions, in racetrack devices through hydrogen gating. With gating times as short as 50 μs and endurance of more than 10,000 cycles, our method provides a powerful means to tune ferrimagnetic spin textures and dynamics, with broad applicability in the rapidly emerging field of ferrimagnetic spintronics.