Domain-induced anomaly of the spin-wave frequency in perpendicularly magnetized Ni(001) ultrathin films

Abstract

Epitaxial Cu/Ni/Cu/Si(001) magnetic films have been studied in the thickness range (17–120 Å) where a uniaxial anisotropy favoring the direction perpendicular to the film plane is dominant over the easy-plane dipolar interaction. Using magneto-optic magnetometry and Brillouin light scattering we show that on decreasing an in-plane magnetic field the perpendicular component of the magnetization breaks into domains.

Signatures of relativistic spin-light coupling in magneto-optical pump-probe experiments

“…The opto-magnetic field can do so, in contrast, and hence, cause a fast modification of the magnetization direction. For nanometer-thick Ni films the magnetization can be reversed with magnetic fields of about 10-20 mT [76]. The opto-magnetic field is smaller, but it can nonetheless be expected to induce a measurable change of the magnetization.…”

Absence of stable collinear configurations in Ni(001) ultrathin films: Canted domain structure as ground state

“…3,7,9,10 Assuming the perpendicular state to be stable, the frequency Ω 0 of the uniform mode versus H, an external magnetic field applied within the film plane, is predicted to have a minimum at a critical field H c . 11 In a previous paper, 12 we reported Brillouin light scattering (BLS) experiments in Cu/Ni/Cu/Si(001) films which, in the thickness range 17 Å≤ t ≤ 80 Å, showed a monotonic decrease of the frequency of the uniform mode on decreasing the in-plane field down to 2 kOe, with a clear change in slope at field values H * ≈ (5-8) kOe, depending on the film thickness. (A similar behavior was observed also in other systems: Co/Au ultrathin films, 13 Co/Pd multilayers, 14 and Co/Au multilayers.…”

“…, a "lower" instability (quite similar to the "upper" one at H > c ) is expected. 17 The fact that, on decreasing H, the Brillouin light scattering data 12 did not show any indication for the low field phase might be interpreted as due to a metastability phenomenon.…”

“…15 ) We attributed such a discrepancy between our data and theoretical predictions 11 to the breakdown of the collinear ground state state and to the onset of a domain configuration. 12 As a matter of fact, spin-wave theory [16][17][18] predicts such an instability at a field value H > c = H c + ∆H c (see Section V for the definitions of H c and ∆H c ) and at a finite wavevector k , whose inverse sets the initial size of the domains. In our previous paper 12 strong evidence for the presence of domains was provided by magneto-optical vectormagnetometry (MOKE-VM) data.…”

“…12 As a matter of fact, spin-wave theory [16][17][18] predicts such an instability at a field value H > c = H c + ∆H c (see Section V for the definitions of H c and ∆H c ) and at a finite wavevector k , whose inverse sets the initial size of the domains. In our previous paper 12 strong evidence for the presence of domains was provided by magneto-optical vectormagnetometry (MOKE-VM) data. A direct visualization of up and down perpendicular domains in these specimens for zero applied field was presented by Hug et al; 19 unfortunately, our present attempts to visualize -using magnetic force microscopy -the domain structure while applying an in-plane magnetic field were unsuccessful due to the very weak magnetic signal from the sample and to the interference with the strong external field.…”