Electric field control of magnetism in Si3N4 gated Pt/Co/Pt heterostructures

Abstract

In this work we show the presence of a magnetoelectric coupling in silicon-nitride gated Pt/Co/Pt heterostructures using X-ray photoemission electron microscopy (XPEEM). We observe a change in magnetic anisotropy in the form of domain wall nucleation and a change in the rate of domain wall fluctuation as a function of the applied electric field to the sample. We also observe the coexistence of in-plane and out of plane magnetization in Pt/Co/Pt heterostructures in a region around the spin reorientation transition whose formation is attributed to substrate surface roughness comparable to the film thickness; with such domain configuration, we find that the in-plane magnetization is more sensitive to the applied electric field than out of plane magnetization. Although we find an effective magnetoelectric coupling in our system, the presence of charge defects in the silicon nitride membranes hampers a systematic electrostatic control of the magnetization.

Meronlike Spin Textures in In-Plane-Magnetized Thin Films

“…The domainwall creep suggests the presence of pinning centers for domain-wall displacement, likely caused by local variations in surface morphology and anisotropy. With a negative applied voltage, the domain configuration remains largely unchanged, which we attribute to an increase in the magnetic anisotropy favoring a single domain state, as also suggested by a decrease in the frequency of thermal fluctuations in the XMCD image sequence at negative voltages [51]. During the nucleation of the reverse in-plane domains with the applied voltage, we find that the out-of-plane spins in the regions where nucleation occurred remain largely unchanged; this is shown by the area marked in white in Figs.…”

“…Note that we prepare two film batches from different deposition systems on both Si 3 N 4 and SiO x substrates across a series of thicknesses, showing consistent results, i.e., both XPEEM and magnetometry results show dominant in-plane magnetization, with a strong perpendicular anisotropy (−1.1 MA/m 3 ) that is insufficient to overcome the magnetostatic shape anisotropy (1.3 MA/m 3 ). On the other hand, Pt/Co/Pt films grown under similar conditions exhibit out of plane magnetization [51], indicating that the in-plane magnetic state is related to the Co/Ta interface.…”

“…Finally, we consider the effect of applying an electric field across the Si 3 N 4 gate dielectric, motivated by our previous observation of a modulation in the magnetic anisotropy of Si 3 N 4 -gated Pt/Co/Pt heterostructures [51]. The measurement configuration is shown in Fig.…”

“…Here, we report the formation of out-of-plane spin structures induced by the DMI in a single trilayer of Ta/Co/Pt exhibiting a dominant in-plane magnetic anisotropy. Further, we observe a magnetoelectric coupling in Si 3 N 4 /Ta/Co/Pt using silicon nitride as a gate dielectric [51], manifest through large changes in the magnetic configuration with an applied electric field.…”

“…Sample set B (grown at the Paul Scherrer Institute) is deposited in a system with a base pressure of 10 −7 mbar under an Ar flow of 5 sccm (corresponding to a chamber pressure of about 2.5 × 10 −3 mbar) using a power For the Si 3 N 4 case, the surface lateral-correlation length is estimated as ξ = 46 nm, giving an average radius of curvature (approximately ξ 2 /16σ ) of 100 nm. Importantly, the Ta layer interfacing the silicon nitride membrane is kept at 1 nm to maximize the magnetoelectric coupling effect and also acts to protect the Co from surface adsorbates [51]. Finally, reference markers made of Cr are patterned by electron-beam lithography used in x-ray photoemission electron microscopy (XPEEM) for sample and image alignment.…”