16 research outputs found
Anisotropic and controllable Gilbert-Bloch dissipation in spin valves
Spin valves form a key building block in a wide range of spintronic concepts
and devices from magnetoresistive read heads to spin-transfer-torque
oscillators. We elucidate the dependence of the magnetic damping in the free
layer on the angle its equilibrium magnetization makes with that in the fixed
layer. The spin pumping-mediated damping is anisotropic and tensorial, with
Gilbert- and Bloch-like terms. Our investigation reveals a mechanism for tuning
the free layer damping in-situ from negligible to a large value via the
orientation of fixed layer magnetization, especially when the magnets are
electrically insulating. Furthermore, we expect the Bloch contribution that
emerges from the longitudinal spin accumulation in the non-magnetic spacer to
play an important role in a wide range of other phenomena in spin valves
Proximity-Enhanced Magnetocaloric Effect in Ferromagnetic Trilayers
The demagnetization and associated magnetocaloric effect in
strong-weak-strong ferromagnetic trilayers, upon a reorientation of the strong
ferromagnets from parallel to antiparallel magnetization, is simulated using
atomistic spin dynamics. The simulations yield non-trivial spin distributions
in the antiparallel state, which in turn allows entropy to be calculated
directly. Empirical functional forms are obtained for the magnetization
distribution in the spacer, differing significantly from some of the commonly
used models. Finally, we find that the magnetocaloric effect in the system can
be significantly improved by allowing the local exchange to vary through the
spacer, which in practice can be implemented by spatially tailoring the
spacer's magnetic dilution.Comment: 8 pages, 6 figure
Sub-Wavelength Terahertz Spin-Flip Laser Based on a Magnetic Point-Contact Array
We present a novel design for a single-mode, truly sub-wavelength THz disk
laser based on a nano-composite gain medium comprising an array of
metal/ferromagnetic point contacts embedded in a thin dielectric layer.
Stimulated emission of light occurs in the point contacts as a result of
spin-flip relaxation of spin-polarized electrons that are injected from the
ferromagnetic side of the contacts. Ultra-high electrical current densities in
the contacts and a dielectric material with a large refractive index, neither
condition being achievable in conventional semiconductor media, allows the
thresholds of lasing to be overcome for the lowest-order modes of the disk,
hence making single-mode operation possible.Comment: 9 pages,4 figure
All-electrical operation of a Curie-switch at room temperature
We present all-electrical operation of a FeCr-based Curie switch
at room temperature. More specifically, we study the current-induced
thermally-driven transition from ferromagnetic to antiferromagnetic
Ruderman-Kittel-Kasuya-Yosida (RKKY) indirect coupling in a
Fe/Cr/FeCr/Cr/Fe multilayer. Magnetometry measurements at
different temperatures show that the transition from the ferromagnetic to the
antiferromagnetic coupling at zero field is observed at 325K. Analytical
modelling confirms that the observed temperature-dependent transition from
indirect ferromagnetic to indirect antiferromangetic interlayer exchange
coupling originates from the modification of the effective interlayer exchange
constant through the ferromagnetic-to-paramagnetic transition in the
FeCr spacer with minor contributions from the
thermally-driven variations of the magnetization and magnetic anisotropy of the
Fe layers. Room-temperature current-in-plane magnetotransport measurements on
the patterned Fe/Cr/FeCr/Cr/Fe strips show the transition
from the 'low-resistance' parallel to the 'high-resistance' antiparallel
remanent magnetization configuration, upon increased probing current density.
Quantitative comparison of the switching fields, obtained by magnetometry and
magnetotransport, confirms that the Joule heating is the main mechanism
responsible for the observed current-induced resistive switching.Comment: 8 pages, 4 figure
Relaxation-free and inertial switching in synthetic antiferromagnets subject to super-resonant excitation
Applications of magnetic memory devices greatly benefit from ultra-fast, low-power switching. Here we propose how this can be achieved efficiently in a nano-sized synthetic antiferromagnet by using perpendicular-to-the-plane picosecond-range magnetic field pulses. Our detailed micromagnetic simulations, supported by analytical results, yield the parameter space where inertial switching and relaxation-free switching can be achieved in the system. We furthermore discuss the advantages of dynamic switching in synthetic antiferromagnets and, specifically, their relatively low-power switching as compared to that in single ferromagnetic particles. Finally, we show how excitation of spin-waves in the system can be used to significantly reduce the post-switching spin oscillations for practical device geometries.QC 20160524</p
Relaxation-free and inertial switching in synthetic antiferromagnets subject to super-resonant excitation
Applications of magnetic memory devices greatly benefit from ultra-fast, low-power switching. Here we propose how this can be achieved efficiently in a nano-sized synthetic antiferromagnet by using perpendicular-to-the-plane picosecond-range magnetic field pulses. Our detailed micromagnetic simulations, supported by analytical results, yield the parameter space where inertial switching and relaxation-free switching can be achieved in the system. We furthermore discuss the advantages of dynamic switching in synthetic antiferromagnets and, specifically, their relatively low-power switching as compared to that in single ferromagnetic particles. Finally, we show how excitation of spin-waves in the system can be used to significantly reduce the post-switching spin oscillations for practical device geometries.QC 20160524</p