Spintronic devices currently rely on magnetic switching or controlled motion of domain walls by an external magnetic field or spin-polarized current. Achieving the same degree of magnetic controllability using an electric field has potential advantages including enhanced functionality and low power consumption. Here we report on an approach to electrically control local magnetic properties, including the writing and erasure of regular ferromagnetic domain patterns and the motion of magnetic domain walls, in CoFe-BaTiO3 heterostructures. Our method is based on recurrent strain transfer from ferroelastic domains in ferroelectric media to continuous magnetostrictive films with negligible magnetocrystalline anisotropy. Optical polarization microscopy of both ferromagnetic and ferroelectric domain structures reveals that domain correlations and strong inter-ferroic domain wall pinning persist in an applied electric field. This leads to an unprecedented electric controllability over the ferromagnetic microstructure, an accomplishment that produces giant magnetoelectric coupling effects and opens the way to electric-field driven spintronics.

Perpendicularly magnetized layers are used widely for high-density information storage in magnetic hard disk drives and nonvolatile magnetic random access memories. Writing and erasing of information in these devices is implemented by magnetization switching in local magnetic fields or via intense pulses of electric current. Improvements in energy efficiency could be obtained when the reorientation of perpendicular magnetization is controlled by an electric field. Here, we report on reversible electric-field-driven out-of-plane to in-plane magnetization switching in Cu/Ni multilayers on ferroelectric BaTiO 3 at room temperature. Fully deterministic magnetic switching in this hybrid material system is based on efficient strain transfer from ferroelastic domains in BaTiO 3 and the high sensitivity of perpendicular magnetic anisotropy in Cu/Ni to electric-field-induced strain modulations. We also demonstrate that the magnetoelectric coupling effect can be used to realize 180°magnetization reversal if the out-of-plane symmetry of magnetic anisotropy is temporarily broken by a small magnetic field.

Control of magnetic domain-wall motion by electric fields has recently attracted scientific attention because of its potential for magnetic logic and memory devices. Here, we report on a new driving mechanism that allows for magnetic domain-wall motion in an applied electric field without the concurrent use of a magnetic field or spin-polarized electric current. The mechanism is based on elastic coupling between magnetic and ferroelectric domain walls in multiferroic heterostructures. Pure electric-field-driven magnetic domain-wall motion is demonstrated for epitaxial Fe films on BaTiO 3 with in-plane and out-ofplane polarized domains. In this system, magnetic domain-wall motion is fully reversible and the velocity of the walls varies exponentially as a function of out-of-plane electric-field strength.

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We report on the generation and confinement of short-wavelength spin waves in a continuous film with periodically modulated magnetic anisotropy. The concept, which is demonstrated for strain-coupled Co 40 Fe 40 B 20 =BaTiO 3 heterostructures, relies on abrupt rotation of magnetic anisotropy at the boundaries of magnetic stripe domains. In combination with an external bias field, this modulation of magnetic anisotropy produces a lateral variation of the effective magnetic field, leading to local spin-wave excitation when irradiated by a microwave magnetic field. In domains with small effective field, spin waves are perfectly confined by the spin gap in neighboring domains. In contrast, standing spin waves in domains with large effective field radiate into neighboring domains. Using micromagnetic simulation, we show that the wavelength of emitted spin waves is tunable from a few micrometers down to about 100 nm by rotation of the bias field. Importantly, the orientation of the wave front remains fixed. We also demonstrate that dynamic fluctuations of the effective magnetic field produce exchange-dominated spin waves at singleanisotropy boundaries. The multiferroic heterostructures presented here enable the use of global excitation fields from a microwave antenna to emit tunable spin waves from a nanometer-wide line source at welldefined locations of a continuous ferromagnetic film.

We present an investigation of the influence of low levels of chemical substitution on the magnetic ground state and Néel skyrmion lattice (SkL) state in GaV 4 S 8-y Se y , where y = 0, 0.1, 7.9, and 8. Muon-spin spectroscopy (μSR) measurements on y = 0 and 0.1 materials reveal the magnetic ground state consists of microscopically coexisting incommensurate cycloidal and ferromagnetic environments, whereas chemical substitution leads to the growth of localized regions of increased spin density. μSR measurements of emergent low-frequency skyrmion dynamics show that the SkL exists under low levels of substitution at both ends of the series. Skyrmionic excitations persist to temperatures below the equilibrium SkL in substituted samples, suggesting the presence of skyrmion precursors over a wide range of temperatures.

We report on domain formation and magnetization reversal in epitaxial Fe films on ferroelectric BaTiO3 substrates with ferroelastic a − c stripe domains. The Fe films exhibit biaxial magnetic anisotropy on top of c domains with out-of-plane polarization, whereas the in-plane lattice elongation of a domains induces uniaxial magnetoelastic anisotropy via inverse magnetostriction. The strong modulation of magnetic anisotropy symmetry results in full imprinting of the a − c domain pattern in the Fe films. Exchange and magnetostatic interactions between neighboring magnetic stripes further influence magnetization reversal and pattern formation within the a and c domains.Ferromagnetic pattern formation via efficient coupling to ferroelectric domain structures has recently been demonstrated. 1-6 Direct correlations between ferromagnetic and ferroelectric domains and its persistence during ferroelectric polarization reversal open up promising ways for electric-field control of local magnetic switching 1-5 and the motion of magnetic domain walls. 6 In systems based on interlayer strain transfer, the ferroelastic domain structure of a ferroelectric material induces local magnetoelastic anisotropies in a ferromagnetic film via inverse magnetostriction. Within the ferromagnetic sub-system, the magnetoelastic anisotropy competes with intrinsic magnetic properties including magnetocrystalline anisotropy and exchange and magnetostatic interactions between domains. Consequently, the evolution of the magnetic microstructure in an applied magnetic or electric field depends critically on the two ferroic materials, the ferromagnetic layer thickness, and the ferroelastic domain size.

Citation for published item:prnkeD u¡ evin tF eF nd ruddrtD fenjmin wF nd rikenD homs tF nd ioD pn nd flundellD tephen tF nd rttD prnis vF nd grisntiD wrt nd frkerD toel eF F nd glrkD tewrt tF nd § tefn § i § D ele § s nd rtnenD woni giomg nd flkrishnnD qeeth nd vnsterD om @PHIVA 9wgneti phses of skyrmionEhosting qRVyey @y a HD PD RD VA proed with muon spetrosopyF9D hysil review fFD WV @SAF HSRRPVF Further information on publisher's website: eprinted with permission from the emerin hysil oietyX prnkeD u¡ evin tF eFD ruddrtD fenjmin wFD rikenD homs tFD ioD pnD flundellD tephen tFD rttD prnis vFD grisntiD wrtD frkerD toel eF FD glrkD tewrt tFD § tefn § i § D ele § sD rtnenD woni giomgD flkrishnnD qeeth vnsterD om @PHIVAF wgneti phses of skyrmionEhosting qRVyey @y a HD PD RD VA proed with muon spetrosopyF hysil eview f WV@SAX HSRRPVF @PHIVA y the emerin hysil oietyF eders my viewD rowseD ndGor downlod mteril for temporry opying purposes onlyD provided these uses re for nonommeril personl purposesF ixept s provided y lwD this mteril my not e further reproduedD distriutedD trnsmittedD modi(edD dptedD performedD displyedD pulishedD or sold in whole or prtD without prior written permission from the emerin hysil oietyFAdditional information:Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. We present the results of a muon-spin spectroscopy investigation of GaV 4 S 8−y Se y with y = 0, 2, 4, and 8. Zero-field measurements suggest that GaV 4 Se 8 and GaV 4 S 8 have distinct magnetic ground states, with the latter material showing an anomalous temperature dependence of the local magnetic field. It is not possible to evolve the magnetic state continuously between these two systems, with the intermediate y = 2 and 4 materials showing glassy magnetic behavior at low temperature. The skyrmion lattice (SkL) phase is evident in the y = 0 and 8 materials through an enhanced response of the muon-spin relaxation to the emergent dynamics that accompany the SkL. For our polycrystalline samples of GaV 4 Se 8 , this enhanced dynamic response is confined to a smaller region of the magnetic field-temperature phase diagram than the previous reports of the SkL in single crystals.