Fast strain wave induced magnetization changes in long cobalt bars: Domain motion versus coherent rotation

Abstract

A high frequency (88 MHz) traveling strain wave on a piezoelectric substrate is shown to change the magnetization direction in 40 lm wide Co bars with an aspect ratio of 10 3 . The rapidly alternating strain wave rotates the magnetization away from the long axis into the short axis direction, via magnetoelastic coupling. Strain-induced magnetization changes have previously been demonstrated in ferroelectric/ferromagnetic heterostructures, with excellent fidelity between the ferromagnet and the ferroelectric domains, but these experiments were limited to essentially dc frequencies. Both magneto-optical Kerr effect and polarized neutron reflectivity confirm that the traveling strain wave does rotate the magnetization away from the long axis direction and both yield quantitatively similar values for the rotated magnetization. An investigation of the behavior of short axis magnetization with increasing strain wave amplitude on a series of samples with variable edge roughness suggests that the magnetization reorientation that is seen proceeds solely via coherent rotation. Polarized neutron reflectivity data provide direct experimental evidence for this model. This is consistent with expectations that domain wall motion cannot track the rapidly varying strain. V C 2015 AIP Publishing LLC. [http://dx

Strong reduction of the coercivity by a surface acoustic wave in an out-of-plane magnetized epilayer

“…The SAW could thus-in theory-affect both steps of the reversal. It has been argued, however [16], that the high frequencies of SAWs (>100 MHz) would not allow enough time for the relatively slow DW propagation (speeds of tens of ms −1 in GaMnAs [27])-unless particular geometries are used [17]so we focus on their effect on nucleation. The concavity of the magnetic aftereffect curves taken under SAW [inset of Fig.…”

“…Relying on this coupling, recent work has predicted [12,13] and demonstrated experimentally [14] that acoustic waves can trigger resonant precessional switching. SAWs can moreover assist-nonresonantly-the coherent reversal of small structures [15,16], or in larger samples could trigger the nucleation or propagation of domain walls [13,17]. In that case, the lever is expected to be the dependency of the domain wall energy on the magnetoelastic constant.…”

Optimizing magneto-optical effects in the ferromagnetic semiconductor GaMnAs

“…This has been made possible thanks to the huge sensitivity of the magnetic anisotropy to strain [14,15]. Strain waves like SAWs have been identified as a powerful tool for magnetization switching in magneto-strictive materials [16,17,18]. In GaMnAs it was recently demonstrated that magnetization precession can be resonantly driven by a SAW when both the magnon and phonon frequencies match [13], which is the first necessary step toward precessional switching [12].…”

Field-Free Magnetization Switching by an Acoustic Wave

“…For the latter two however [2][3][4][5][6][7], the necessity for biasing fields remains ubiquitous, whether spin-transfer, spin-orbit torques, or electric-field modulations of the anisotropy are at play. A recently developed alternative for magnetization switching is the use of acoustic waves [8][9][10][11][12][13][14][15]. The effective field generated by Rayleigh waves through inverse magnetostriction can switch magnetization efficiently in magnetostrictive thin films of both in-plane and out-of-plane anisotropies [14,15].…”