Electrical Manipulation of Oxygen Ion Migrations for the Voltage‐Controlled Adjustment of Magnetic Anisotropy and Optimized Skyrmion Generations

Abstract

recognized that many different mechanisms are implementable, hence the modulation of carrier density, [1][2][3][4] piezoelectric strain effect, [5][6][7][8][9] exchange coupling, [10][11][12][13] orbital reconstruction, [14][15][16][17] and electrochemical effect [18][19][20] in various magnetoelectric coupling systems, consisting of an ferromagnet (FM), antiferromagnet (AFM), as well as ferroelectric (FE) materials in the thin film structures have been actively investigated. It is also noted that the relevant magnetic properties manipulated by VCMA include magnetization, magnetoresistance (MR), magnetic anisotropy (MA), coercivity (H C ), exchange bias field (H E ), and curie temperature (T C ), and the impact of VCMA technology in the application of magnetic material can be broadly extended to many areas. In the present article, we demonstrate that a transformation of magnetic anisotropy can be achieved at room temperature by electro-chemical effect at the interface between Co layer and Gd layer based on voltage-driven O 2− ion migrations within the amorphous Gd-O layer in Pt/Co/Gd/ GdO x /Pt multilayers structure. As the ion migration can be bidirectional depending on the polarity of applied voltage, magnetic anisotropy of the Co film could be reversibly transformed between perpendicular magnetic anisotropy (PMA) and inplane magnetic anisotropy (IMA). Unlike the recently reported VCMA results realized by the ionic migration mechanism accompanied with fully oxidation of FM metal layer, [18,19,21] present work here reports a large modulation in MA (≈4500 fJ/Vm) of the FM layer at room temperature without fully oxidizing the atoms in FM layer, thereby there is no need to sacrifice the magnetization. Change of MA is mainly from an induced PMA in the transition metal/oxide interface with the interfacial hybridization of transition metal and oxygen. [22][23][24] In order to further explore the MA control, domain morphology in FM was also examined. Many recent studies reported that skyrmions can be set in PMA films with stripe domain morphology by appropriately adjusting their MA and the domain widths via applications of external magnetic field [25,26] combined with thermal assistances. [27,28] Recent attentions to skyrmions are not only for a fundamental understanding of their topological With the prospect of energy-efficient spintronics by voltage-controlled magnetic anisotropy (VCMA), various mechanisms are investigated involving electron orbital state modulations for enhanced spin-orbit interactions, couplings with piezoelectric strain, and electrochemical effect at the interface within diverse magnetoelectric coupled material systems. In the present work, chemistry and spatial distributions of atoms are fine-tuned at the interface between ferromagnetic Co and partially oxidized Gd layers via voltage-controlled ion migrations, achieving highly sensitive and stable VCMA operations. With combined actions of chemical diffusion and electrical driving of oxygen through amorphous Gd layer, asymmetric electrical adjustm...

Selectively Controlled Ferromagnets by Electric Fields in van der Waals Ferromagnetic Heterojunctions

“…Controlling magnetic properties of FGT by charge transfer in our work is essentially different from the reported voltage-controlled magnetic anisotropy (VCMA) in the literature, − although the latter can also be achieved by modulation of carrier density , in addition to the piezoelectric strain effect − and the electrochemical effect. , There are pretty clear differences between that and our work: In conventional VCMA, the carrier density is usually modulated by gate voltages, where the carrier depletion and accumulation happen at the interface between insulator and ferromagnet. Thus, the modulation of carrier density in the conventional VCMA only applies for ultrathin ferromagnetic metals of a few nanometers due to the short screening length. , In contrast, the magnetic anisotropy for the relatively thick FGT electrodes (∼10–20 nm) is effectively tuned in our experiment due to the electric current directly passing through the FGT/CGT/FGT junction.…”

Voltage-controlled bimeron diode-like effect in nanoscale information channel

“…Recently, some researchers have reported observation of the bimeron and the skyrmion in experiments [34,35], and control of the skyrmion through voltage-controlled magnetic anisotropy (VCMA) [36]. Besides, the observation of domain wall bimerons [37] and transformation between bimeron and skyrmion has also been reported [38], which provides a good idea for spin topology to be used in storage applications.…”

Voltage-controlled magnetic solitons motion in an anisotropic ferromagnetic nanowire

“…Comparing to current or magnetic fields manipulation, the voltage control scheme is more attractive due to its feasible features, such as simple manipulation techniques for nanoscale applications, low cost, and no magnetic hysteresis [21][22][23][24][25]. In recent years, the voltage-controlled magnetic anisotropy (VCMA) effect has gained widespread attention as a promising technology [3,[26][27][28][29][30].…”