166 research outputs found
Magnetic resonance spectroscopy of perpendicularly magnetized permalloy multilayer disks
Using a Magnetic Resonance Force Microscope, we compare the ferromagnetic
resonance spectra of individual micron-size disks with identical diameter, 1
m, but different layer structures. For a disk composed of a single 43.3 nm
thick permalloy (Py) layer, the lowest energy mode in the perpendicular
configuration is the uniform precession. The higher energy modes are standing
spin-waves confined along the diameter of the disk. For a Cu(30)/Py(100)/Cu(30)
nm multilayer structure, it has been interpreted that the lowest energy mode
becomes a precession localized at the Cu/Py interfaces. When the multilayer is
changed to Py(100)/Cu(10)/Py(10) nm, this localized mode of the thick layer is
coupled to the precession of the thin layer
Essais sur l'administration de la Castille au XVIème siècle
Copia digital. Valladolid : Junta de Castilla y León. Consejería de Cultura y Turismo, 2009-2010Contiene: Fac-simile de ¿'attestation délivrée en l'année 834 à Teudéfréde, refugié espagnol, relativement au firef de Fontjoncouse, donné á Jean, son père, par Charlemagne et Louis le Dèbonnaire (réduction au quqrt superficiel de l¡original dèposé aux archives de l'aude
Measurement of the intrinsic damping constant in individual nanodisks of YIG and YIG{\textbar}Pt
We report on an experimental study on the spin-waves relaxation rate in two
series of nanodisks of diameter 300, 500 and 700~nm, patterned out of
two systems: a 20~nm thick yttrium iron garnet (YIG) film grown by pulsed laser
deposition either bare or covered by 13~nm of Pt. Using a magnetic resonance
force microscope, we measure precisely the ferromagnetic resonance linewidth of
each individual YIG and YIG{\textbar}Pt nanodisks. We find that the linewidth
in the nanostructure is sensibly smaller than the one measured in the extended
film. Analysis of the frequency dependence of the spectral linewidth indicates
that the improvement is principally due to the suppression of the inhomogeneous
part of the broadening due to geometrical confinement, suggesting that only the
homogeneous broadening contributes to the linewidth of the nanostructure. For
the bare YIG nano-disks, the broadening is associated to a damping constant
. A 3 fold increase of the linewidth is observed for
the series with Pt cap layer, attributed to the spin pumping effect. The
measured enhancement allows to extract the spin mixing conductance found to be
for our
YIG(20nm){\textbar}Pt interface, thus opening large opportunities for the
design of YIG based nanostructures with optimized magnetic losses.Comment: 4 pages, 3 figure
Electronic control of the spin-wave damping in a magnetic insulator
It is demonstrated that the decay time of spin-wave modes existing in a
magnetic insulator can be reduced or enhanced by injecting an in-plane dc
current, , in an adjacent normal metal with strong spin-orbit
interaction. The demonstration rests upon the measurement of the ferromagnetic
resonance linewidth as a function of in a 5~m diameter
YIG(20nm){\textbar}Pt(7nm) disk using a magnetic resonance force microscope
(MRFM). Complete compensation of the damping of the fundamental mode is
obtained for a current density of , in
agreement with theoretical predictions. At this critical threshold the MRFM
detects a small change of static magnetization, a behavior consistent with the
onset of an auto-oscillation regime.Comment: 6 pages 4 figure
Spin-torque driven ferromagnetic resonance of Co/Ni synthetic layers in spin valves
Spin-torque driven ferromagnetic resonance (ST-FMR) is used to study thin
Co/Ni synthetic layers with perpendicular anisotropy confined in spin-valve
based nanojunctions. Field swept ST-FMR measurements were conducted with a
magnetic field applied perpendicular to the layer surface. The resonance lines
were measured under low amplitude rf excitation, from 1 to 20 GHz. These
results are compared with those obtained using conventional rf field driven FMR
on extended films with the same Co/Ni layer structure. The layers confined in
spin valves have a lower resonance field, a narrower resonance linewidth and
approximately the same linewidth vs frequency slope, implying the same damping
parameter. The critical current for magnetic excitations is determined from
measurements of the resonance linewidth vs dc current and is in accord with the
one determined from I-V measurements.Comment: 3 pages, 3 figure
On-chip Integration of High-Frequency Electron Paramagnetic Resonance Spectroscopy and Hall-Effect Magnetometry
A sensor that integrates high sensitivity micro-Hall effect magnetometry and
high-frequency electron paramagnetic resonance spectroscopy capabilities on a
single semiconductor chip is presented. The Hall-effect magnetometer was
fabricated from a two dimensional electron gas GaAs/AlGaAs heterostructure in
the form of a cross, with a 50x50 um2 sensing area. A high-frequency microstrip
resonator is coupled with two small gaps to a transmission line with a 50 Ohms
impedance. Different resonator lengths are used to obtain quasi-TEM fundamental
resonant modes in the frequency range 10-30 GHz. The resonator is positioned on
top of the active area of the Hall-effect magnetometer, where the magnetic
field of the fundamental mode is largest, thus optimizing the conversion of
microwave power into magnetic field at the sample position. The two gaps
coupling the resonator and transmission lines are engineered differently. The
gap to the microwave source is designed to optimize the loaded quality factor
of the resonator (Q = 150) while the gap for the transmitted signal is larger.
This latter gap minimizes losses and prevents distortion of the resonance while
enabling measurement of the transmitted signal. The large filling factor of the
resonator permits sensitivities comparable to that of high-quality factor
resonant cavities. The integrated sensor enables measurement of the
magnetization response of micron scale samples upon application of microwave
fields. In particular, the combined measurement of the magnetization change and
the microwave power under cw microwave irradiation of single crystal of
molecular magnets is used to determine of the energy relaxation time of the
molecular spin states. In addition, real time measurements of the magnetization
dynamics upon application of fast microwave pulses are demonstratedComment: Submitted to Review of Scientific Instrument
Spin torque resonant vortex core expulsion for an efficient radio-frequency detection scheme
Spin-polarised radio-frequency currents, whose frequency is equal to that of
the gyrotropic mode, will cause an excitation of the core of a magnetic vortex
confined in a magnetic tunnel junction. When the excitation radius of the
vortex core is greater than that of the junction radius, vortex core expulsion
is observed, leading to a large change in resistance, as the layer enters a
predominantly uniform magnetisation state. Unlike the conventional spin-torque
diode effect, this highly tunable resonant effect will generate a voltage which
does not decrease as a function of rf power, and has the potential to form the
basis of a new generation of tunable nanoscale radio-frequency detectors
- …