49 research outputs found
Determination of the spin Hall angle, spin mixing conductance and spin diffusion length in Ir/CoFeB for spin-orbitronic devices
Iridium is a very promising material for spintronic applications due to its
interesting magnetic properties such as large RKKY exchange coupling as well as
its large spin-orbit coupling value. Ir is for instance used as a spacer layer
for perpendicular synthetic antiferromagnetic or ferrimagnet systems. However,
only a few studies of the spintronic parameters of this material have been
reported. In this paper, we present inverse spin Hall effect - spin pumping
ferromagnetic resonance measurements on CoFeB/Ir based bilayers to estimate the
values of the effective spin Hall angle, the spin diffusion length within
iridium, and the spin mixing conductance in the CoFeB/Ir bilayer. In order to
have reliable results, we performed the same experiments on CoFeB/Pt bilayers,
which behavior is well known due to numerous reported studies. Our experimental
results show that the spin diffusion length within iridium is 1.3 nm for
resistivity of 250 n.m, the spin mixing conductance of the CoFeB/Ir interface is 30 nm, and the spin Hall angle
of iridium has the same sign than the one of platinum and is evaluated at 26%
of the one of platinum. The value of the spin Hall angle found is 7.7% for Pt
and 2% for Ir. These relevant parameters shall be useful to consider Ir in new
concepts and devices combining spin-orbit torque and spin-transfer torque.Comment: 8 pages, 4 figure
Two types of all-optical magnetization switching mechanisms using femtosecond laser pulses
Magnetization manipulation in the absence of an external magnetic field is a
topic of great interest, since many novel physical phenomena need to be
understood and promising new applications can be imagined. Cutting-edge
experiments have shown the capability to switch the magnetization of magnetic
thin films using ultrashort polarized laser pulses. In 2007, it was first
observed that the magnetization switching for GdFeCo alloy thin films was
helicity-dependent and later helicity-independent switching was also
demonstrated on the same material. Recently, all-optical switching has also
been discovered for a much larger variety of magnetic materials (ferrimagnetic,
ferromagnetic films and granular nanostructures), where the theoretical models
explaining the switching in GdFeCo films do not appear to apply, thus
questioning the uniqueness of the microscopic origin of all-optical switching.
Here, we show that two different all-optical switching mechanisms can be
distinguished; a "single pulse" switching and a "cumulative" switching process
whose rich microscopic origin is discussed. We demonstrate that the latter is a
two-step mechanism; a heat-driven demagnetization followed by a
helicity-dependent remagnetization. This is achieved by an all-electrical and
time-dependent investigation of the all-optical switching in ferrimagnetic and
ferromagnetic Hall crosses via the anomalous Hall effect, enabling to probe the
all-optical switching on different timescales.Comment: 1 page, LaTeX; classified reference number
Spectroscopic studies of GTA welding plasmas. Temperature calculation and dilution measurement
International audienc
Understanding nanoscale temperature gradients in magnetic nanocontacts
We determine the temperature profile in magnetic nanocontacts submitted to
the very large current densities that are commonly used for spin-torque
oscillator behavior. Experimentally, the quadratic current-induced increase of
the resistance through Joule heating is independent of the applied temperature
from 6 K to 300 K. The modeling of the experimental rate of the current-induced
nucleation of a vortex under the nanocontact, assuming a thermally-activated
process, is consistent with a local temperature increase between 150 K and 220
K. Simulations of heat generation and diffusion for the actual tridimensional
geometry were conducted. They indicate a temperature-independent efficiency of
the heat sinking from the electrodes, combined with a localized heating source
arising from a nanocontact resistance that is also essentially
temperature-independent. For practical currents, we conclude that the local
increase of temperature is typically 160 K and it extends 450 nm about the
nanocontact. Our findings imply that taking into account the current-induced
heating at the nanoscale is essential for the understanding of magnetization
dynamics in nanocontact systems.Comment: 5 pages, 5 figure