T. Devolder

Current-driven vortex oscillations in metallic nanocontacts.

We present experimental evidence of subgigahertz spin-transfer oscillations in metallic nanocontacts that are due to the translational motion of a magnetic vortex. The vortex is shown to execute large-amplitude orbital motion outside the contact region. Good agreement with analytical theory and micromagnetics simulations is found.

Strain-controlled magnetic domain wall propagation in hybrid piezoelectric/ferromagnetic structures

The control of magnetic order in nanoscale devices underpins many proposals for integrating spintronics concepts into conventional electronics. A key challenge lies in finding an energy-efficient means of control, as power dissipation remains an important factor limiting future miniaturization of integrated circuits. One promising approach involves magnetoelectric coupling in magnetostrictive/piezoelectric systems, where induced strains can bear directly on the magnetic anisotropy. While such processes have been demonstrated in several multiferroic heterostructures, the incorporation of such complex materials into practical geometries has been lacking. Here we demonstrate the possibility of generating sizeable anisotropy changes, through induced strains driven by applied electric fields, in hybrid piezoelectric/spin-valve nanowires. By combining magneto-optical Kerr effect and magnetoresistance measurements, we show that domain wall propagation fields can be doubled under locally applied strains. These results highlight the prospect of constructing low-power domain wall gates for magnetic logic devices.

Spin wave contributions to the high-frequency magnetic response of thin films obtained with inductive methods

The high-frequency magnetic response of Permalloy thin films have been measured using network-analyzer ferromagnetic resonance. We demonstrate that the excitation of spin waves by the coplanar wave-guide modify the magnetic response appreciably, in particular, by causing a frequency shift and broadening of the resonance peak. An analytic theory is presented to account for the experimental observations and provides a quantitative tool to accurately determine the Gilbert damping constant.

Sub-50 nm planar magnetic nanostructures fabricated by ion irradiation

He+ ion irradiation of Co–Pt multilayers through a silica mask obtained by a combination of high resolution lithography and reactive ion etching can produce an optical contrast-free, entirely planar, sub-50 nm magnetically patterned array. Furthermore, the specificity of magnetization reversal in such arrays leads to a weak dispersion of coercive forces. The technique holds promise for both present hard disk technology and future near field magneto-optical recording.

Study of the dynamic magnetic properties of soft CoFeB films

We study the magnetization damping in ion-beam deposited Co72Fe18B10 thin films as a function of film thickness and crystalline state. As-deposited amorphous layers showed low damping (αapp=0.006) that is thickness independent. 40nm Co80Fe20 with no boron content exhibited a value twice higher (αapp=0.013). Crystallization in Co72Fe18B10, triggered by annealing at 280°C, results in increased magnetization as well as a strong increase in damping, by a factor of 5 for 40nm films. For lower thicknesses the damping increase upon annealing is less pronounced. The exchange stiffness constant for amorphous films is deduced from perpendicular standing spin waves to be 28.4×10−12J∕m. The annealing dependence of damping should have consequences for the spin-transfer switching in CoFeB∕MgO∕CoFeB magnetic tunnel junctions.

Interfacial Dzyaloshinskii-Moriya interaction in perpendicularly-magnetized Pt/Co/AlO

Spin waves in perpendicularly magnetized

_x

{\text{Pt/Co/AlO}}_{x}/\text{Pt}

ultrathin films measured by Brillouin light spectroscopy

ultrathin films with varying Co thicknesses (0.6--1.2 nm) have been studied with Brillouin light spectroscopy in the Damon-Eshbach geometry. The measurements reveal a pronounced nonreciprocal propagation, which increases with decreasing Co thickness. This nonreciprocity, attributed to an interfacial Dzyaloshinskii-Moriya interaction (DMI), is significantly stronger than asymmetries resulting from surface anisotropies for such modes. Results are consistent with an interfacial DMI constant

Domain wall displacement induced by subnanosecond pulsed current

{D}_{\mathrm{s}}=\ensuremath{-}1.7\ifmmode\pm\else\textpm\fi{}0.11\phantom{\rule{0.28em}{0ex}}\text{pJ}

Vector network analyzer ferromagnetic resonance of thin films on coplanar waveguides : Comparison of different evaluation methods

/m, which favors left-handed chiral spin structures. This suggests that such films below 1 nm in thickness should support chiral states such as skyrmions at room temperature.