Voltage Control of Perpendicular Magnetic Anisotropy in Multiferroic Composite Thin Films under Strong Electric Fields

Abstract

Metrics & MoreArticle Recommendations * sı Supporting Information ABSTRACT: "Ferroelectric/ferromagnetic" multiferroic composites with perpendicular magnetic anisotropy (PMA) are useful for developing power-efficient magnetic memories. Voltage control of PMA has been demonstrated in bulk multiferroic composites based on ferroelectric single crystals, but they are not compatible for integration. Multiferroic composite thin films are useful for developing integrated devices; however, voltage control of PMA in them has not been achieved yet at room temperature due to their low magnetoelectric (ME) coupling coefficient. Here, we demonstrate such functionality and propose to enhance their ME coupling effect under a strong electric field by taking full advantage of the large dielectric strength of ferroelectric thin films. First, the thickness-dependent breakdown of Pb(Zr 0.384 Ti 0.576 Nb 0.04 )O 3 (PNZT) thin films was studied, and the two-layer (∼200 nm) samples exhibited the highest breakdown strength (3.68 MV/cm) and small surface roughness (<1 nm). Second, we fabricated "PNZT/(Co/ Pt) 5 " thin films with strong PMA whose breakdown strength is nearly independent of the top electrode materials. Finally, voltageinduced effective magnetic field (H eff ) in "PNZT/(Co/Pt) 5 " was studied. It is comparable to that achieved in bulk composites and will induce magnetization switching under strong electric fields. Multiferroic composite thin films with large breakdown strength will provide a useful platform for enabling integrated multiferroic devices.

Characterization of In‐Plane Piezoelectric Strain of Ferroelectric Thin Films by the Magnetoelectric Coupling Effect

“…This strain could directly transfer to the ferromagnetic layer and change its magnetic anisotropy by the magnetoelastic effect. Generally, the applied electric field to the ferroelectric layer induce an effective magnetic field to the ferromagnetic layer that could be expressed as [ 21 ] where λ s is the magnetostriction, M s is the saturation magnetization, Y and ν are the Young's modulus and Poisson's ratio of the ferromagnetic thin films, respectively, S 31 and d 31 are the in‐plane piezostrain and piezoelectric coefficient of the ferroelectric layer, respectively, and E is the applied electric field. Usually, α ME = H eff / E represents the ME coupling coefficient, and K = 3 λ s Y / M s (1 + ν ) is the figure of merit determined by ferromagnetic thin films.…”

“…This strain could directly transfer to the ferromagnetic layer and change its magnetic anisotropy by the magnetoelastic effect. Generally, the applied electric field to the ferroelectric layer induce an effective magnetic field to the ferromagnetic layer that could be expressed as [21] H…”

The modulation of perpendicular magnetic anisotropy and spin–orbit toque in Pt/Co/Pt multilayers with interfacial decoration by insertion of a Bi layer

“…The Ta underlayer is introduced to improve the adhesion of the Pt layer. To investigate the effect of Bi as an inserted layer on PMA and SOT efficiency in Pt/Co/Pt multilayers, we prepared two series of multilayers samples as follows: (I) Ta(3)/Pt(3)/Co(1)/Pt (5) and Ta(3)/Pt(3)/ Co(1)/Bi(2)/Pt(5); (II) Ta(3)/Pt(3)/Co(1)/Pt (1) and Ta(3)/Pt(3)/ Co(1)/Bi(2)/Pt (1). The numbers in parentheses represent the layer thickness in nanometers.…”

“…Multilayer structures comprising heavy-metal/ferromagnetic /heavy-metal (HM/FM/HM) layers with perpendicular magnetic anisotropy (PMA) are crucial for advancing highdensity magnetic random-access memory technology and have been extensively investigated through various experimental approaches. These include studies on voltage manipulation of PMA [1][2][3] and spin-orbit torque (SOT)-mediated magnetization reversal [4][5][6][7], as well as current-induced domain wall motion [8][9][10]. Among these systems, the Pt/Co/Pt multilayer configuration stands out as particularly prominent, showcasing robust PMA.…”

Hydrogen-Controlled Spin Reorientation Transition in a Nanometer-Thick FePd Layer on Co/[Pt/Co]4/Pt Multilayers for Applications in Spintronics

“…Considering the disadvantages of applying an external magnetic field, which requires complicated circuitry and additional power consumption, a field-free SOT switching mechanism should be developed. Numerous efforts have been made to realize field-free SOT switching mechanisms, including achieving lateral structural asymmetry using a wedge-layer, − voltage control in a multiferroic composite, exchange-bias and interlayer exchange coupling, and current-induced field-free switching . Recently, Hwang et al demonstrated the deterministic field-free SOT switching of perpendicular magnetization in amorphous and ferrimagnetic Gd/Co multilayers accompanied by a tilted magnetic anisotropy (TMA) axis, disrupting the symmetry of the PMA in a controlled manner, and providing an opportunity for switching perpendicular magnetization by using tilted anisotropy …”