Voltage control of magnetic anisotropy in Fe films with quantum well states

Abstract

The influence of a gate voltage on magnetic anisotropy is investigated in a thin Fe film epitaxially grown on a Ag(1,1,10) substrate and covered by MgO. Oscillations in step-induced magnetic anisotropy due to quantum well states (QWS) confined in the Fe film are observed and shown to persist up to room temperature at low Fe thicknesses. By systematically examining the voltage and thickness dependence of the magnetic hysteresis loop characteristics, we identify two distinct effects by which an applied voltage modifies the magnetic anisotropy. The first effect is due to voltage-induced changes to interfacial perpendicular magnetic anisotropy which, due to the vicinal geometry, leads to changes in the effective in-plane uniaxial magnetic anisotropy. A second effect is observed at lower film thicknesses and shows nonmonotonic voltage-induced effects on magnetic anisotropy. This nonmonotonic behavior coincides with the onset of significant QWS-induced effects on magnetic anisotropy and suggests a link between QWS-and voltage-induced anisotropy changes.

Research Update: Magnetoionic control of magnetization and anisotropy in layered oxide/metal heterostructures

“…8 Meanwhile, E-modulated magnetic anisotropy 8,16,17,20,21 and magnetization 20,22,24 have been achieved in ultrathin metallic films. In order to apply the electric field, various architectures have been utilized: dielectric layers 14,16,17 as well as solid 25,26 or liquid [20][21][22]24,27 electrolytes. Different interfacial mechanisms are discussed to explain the observed E-induced modulations of magnetism in metallic layers.…”

“…Due to the short screening length, reasonable E-effects in metals are only expected at large interface/volume ratio. Theoretical predictions 12,13 and experimental studies on E-effects on magnetism in Co, 14,15 Fe, [16][17][18] FeRh, 19 and (Fe,Co)Pt [20][21][22] films strongly triggered research efforts. Since for spintronics, the functionality of ferromagnetic metallic layers strongly depends on magnetization and magnetic anisotropy, 23 an E-induced modulation of these properties is anticipated.…”

“…Changes of the electronic band filling in the uppermost atomic layers, obtained by capacitive electronic charging via dielectric layers or electrolytic double layers, have been suggested as origin for E-induced variations of interface and/or magnetocrystalline anisotropy. 16,19,21 Recently, an increasing number of reports points towards an influence of interfacial chemistry. 15,18,20,22,[25][26][27][28][29] The background is that the applied electric field, besides capacitive charging, can induce charge-transfer reactions leading to a reversible change of the oxidation state of, e.g., Fe or Co species.…”

Direct surface charging and alkali-metal doping for tuning the interlayer magnetic order in planar nanostructures

“…Instead, a favorable conditions will be created for other means of spin manipulation mechanisms, e.g. spin transfer torque 7,8 or electrostatic gating 37,62,63 , leading to switching mechanism assisted with alkali metal doping. Therefore, once the energy barrier is completely overcome the system probably settles down to the reversed state.…”

Quantum-well-induced engineering of magnetocrystalline anisotropy in ferromagnetic films

“…[19][20][21] Besides, the value of MAE is measured to increase remarkably by applying a small electric field to charge a Fe film moderately. 13 Such property has great application potential as it persists to a Fe film thicker than 1 nm, 22,23 even though the field is strongly screened in such a thick film. A recent experiment reveals a link between this property and QWSs, 22 but the detailed mechanism remains a puzzle.…”