25 research outputs found
Complete mapping of the spin-wave spectrum in vortex state nano-disk
We report a study on the complete spin-wave spectrum inside a vortex state
nano-disk. Transformation of this spectrum is continuously monitored as the
nano-disk becomes gradually magnetized by a perpendicular magnetic field and
encouters a second order phase transition to the uniformly magnetized state.
This reveals the bijective relationship that exists between the eigen-modes in
the vortex state with the ones in the saturated state. It is found that the
gyrotropic mode can be continuously viewed as a uniform phase precession, which
uniquely softens (its frequency vanishes) at the saturation field to transform
above into the Kittel mode. By contrast the other spin-wave modes remain finite
as a function of the applied field while their character is altered by level
anti-crossing
Comparative Measurements of Inverse Spin Hall and Magnetoresistance in YIG|Pt and YIG|Ta
We report on a comparative study of spin Hall related effects and
magnetoresistance in YIG|Pt and YIG|Ta bilayers. These combined measurements
allow to estimate the characteristic transport parameters of both Pt and Ta
layers juxtaposed to YIG: the spin mixing conductance
at the YIGnormal metal interface, the spin Hall angle , and the
spin diffusion length in the normal metal. The inverse spin Hall
voltages generated in Pt and Ta by the pure spin current pumped from YIG
excited at resonance confirm the opposite signs of spin Hall angles in these
two materials. Moreover, from the dependence of the inverse spin Hall voltage
on the Ta thickness, we extract the spin diffusion length in Ta, found to be
nm. Both the YIG|Pt and YIG|Ta systems
display a similar variation of resistance upon magnetic field orientation,
which can be explained in the recently developed framework of spin Hall
magnetoresistance.Comment: 8 pages, 5 figures, 1 tabl
Detection of the microwave spin pumping using the inverse spin Hall effect
We report electrical detection of the dynamical part of the spin pumping
current emitted during ferromagnetic resonance (FMR) using the inverse Spin
Hall Effect (ISHE). The experiment is performed on a YIGPt bilayer. The
choice of YIG, a magnetic insulator, ensures that no charge current flows
between the two layers and only pure spin current produced by the magnetization
dynamics are transferred into the adjacent strong spin-orbit Pt layer via spin
pumping. To avoid measuring the parasitic eddy currents induced at the
frequency of the microwave source, a resonance at half the frequency is induced
using parametric excitation in the parallel geometry. Triggering this nonlinear
effect allows to directly detect on a spectrum analyzer the microwave component
of the ISHE voltage. Signals as large as 30 V are measured for precession
angles of a couple of degrees. This direct detection provides a novel efficient
means to study magnetization dynamics on a very wide frequency range with great
sensitivity
Mechanical magnetometry of Cobalt nanospheres deposited by focused electron beam at the tip of ultra-soft cantilevers
Using focused-electron-beam-induced deposition, Cobalt magnetic nanospheres
with diameter ranging between 100 nm and 300 nm are grown at the tip of
ultra-soft cantilevers. By monitoring the mechanical resonance frequency of the
cantilever as a function of the applied magnetic field, the hysteresis curve of
these individual nanospheres are measured. This enables to evaluate their
saturation magnetization, found to be around 430 emu/cm^3 independently of the
size of the particle, and to infer that the magnetic vortex state is the
equilibrium configuration of these nanospheres at remanence
Improved spectral stability in spin transfer nano-oscillators: single vortex versus coupled vortices dynamics
We perform a comparative study of spin transfer induced excitation of the
gyrotropic motion of a vortex core with either uniform or vortex spin
polarizers. The microwave output voltage associated with the vortex dynamics,
detected in both cases, displays a strong reduction of phase fluctuations in
the case of the vortex polarizer, with a decrease of the peak linewidth by one
order of magnitude down to 200kHz at zero field. A thorough study of rf
emission features for the different accessible vortex configurations shows that
this improvement is related to the excitation of coupled vortex dynamics by
spin transfer torques
Generation of coherent spin-wave modes in Yttrium Iron Garnet microdiscs by spin-orbit torque
Spin-orbit effects [1-4] have the potential of radically changing the field
of spintronics by allowing transfer of spin angular momentum to a whole new
class of materials. In a seminal letter to Nature [5], Kajiwara et al. showed
that by depositing Platinum (Pt, a normal metal) on top of a 1.3 m thick
Yttrium Iron Garnet (YIG, a magnetic insulator), one could effectively transfer
spin angular momentum through the interface between these two different
materials. The outstanding feature was the detection of auto-oscillation of the
YIG when enough dc current was passed in the Pt. This finding has created a
great excitement in the community for two reasons: first, one could control
electronically the damping of insulators, which can offer improved properties
compared to metals, and here YIG has the lowest damping known in nature;
second, the damping compensation could be achieved on very large objects, a
particularly relevant point for the field of magnonics [6,7] whose aim is to
use spin-waves as carriers of information. However, the degree of coherence of
the observed auto-oscillations has not been addressed in ref. [5]. In this
work, we emphasize the key role of quasi-degenerate spin-wave modes, which
increase the threshold current. This requires to reduce both the thickness and
lateral size in order to reach full damping compensation [8] , and we show
clear evidence of coherent spin-orbit torque induced auto-oscillation in
micron-sized YIG discs of thickness 20 nm
Coherent long-range transfer of angular momentum between magnon Kittel modes by phonons
We report ferromagnetic resonance in the normal configuration of an
electrically insulating magnetic bilayer consisting of two yttrium iron garnet
(YIG) films epitaxially grown on both sides of a 0.5-mm-thick nonmagnetic
gadolinium gallium garnet (GGG) slab. An interference pattern is observed and
it is explained as the strong coupling of the magnetization dynamics of the two
YIG layers either in phase or out of phase by the standing transverse sound
waves, which are excited through a magnetoelastic interaction. This coherent
mediation of angular momentum by circularly polarized phonons through a
nonmagnetic material over macroscopic distances can be useful for future
information technologies
Conduction of spin currents through insulating antiferromagnetic oxides
Damping processes, associated to magnetization dynamics, allow to generate spin currents from precessing ferromagnets. These can be transmitted into adjacent conducting layers through an interface exchange interaction with conduction electrons. It is in principle also possible to inject angular momentum into insulators but the relevant physical mechanisms are not yet identified. In order to test some ideas concerning pure spin transport through insulating oxides, the present paper reports on the behaviour of two materials with very different properties: NiO is an antiferromagnet whereas SiO2 is a non-magnetic light element insulator. While a sizeable flow of angular momentum is found to be able to propagate through nickel oxide, a SiO2 layer as thin as 2 nm completely blocks this transfer. This underlines some essential features required to conduct a spin current, including the presence of either magnetic order through which magnons can propagate, or compounds with large spin-orbit interactions where phonons can carry angular momentum