180 research outputs found
Micromagnetic understanding of stochastic resonance driven by spin-transfertorque
In this paper, we employ micromagnetic simulations to study non-adiabatic
stochastic resonance (NASR) excited by spin-transfer torque in a
super-paramagnetic free layer nanomagnet of a nanoscale spin valve. We find
that NASR dynamics involves thermally activated transitions among two static
states and a single dynamic state of the nanomagnet and can be well understood
in the framework of Markov chain rate theory. Our simulations show that a
direct voltage generated by the spin valve at the NASR frequency is at least
one order of magnitude greater than the dc voltage generated off the NASR
frequency. Our computations also reproduce the main experimentally observed
features of NASR such as the resonance frequency, the temperature dependence
and the current bias dependence of the resonance amplitude. We propose a simple
design of a microwave signal detector based on NASR driven by spin transfer
torque.Comment: 25 pages 8 figures, accepted for pubblication on Phys. Rev.
Resonant excitation of vortex gyrotropic mode via surface acoustic waves
Finding new energy-efficient methods for exciting magnetization dynamics is
one of the key challenges in magnonics. In this work, we present an approach to
excite the gyrotropic dynamics of magnetic vortices through the phenomenon of
inverse magnetostriction, also known as the Villari effect. We develop an
analytical model based on the Thiele formalism that describes the gyrotropic
motion of the vortex core including the energy contributions due to inverse
magnetostriction. Based on this model, we predict excitations of the vortex
core resonances by surface acoustic waves whose frequency is resonant with the
frequency of the vortex core. We verify the model's prediction using
micromagnetic simulations, and show the dependence of the vortex core's
oscillation radius on the surface acoustic wave amplitude and the static bias
field. Our study contributes to the advancement of energy-efficient magnetic
excitations by relying on voltage-induced driven dynamics, which is an
alternative to conventional current-induced excitations
The Impact of an Intense Cyclone on Short-Term Sea Ice Loss in a Fully Coupled Atmosphere-Ocean-Ice Model
AbstractArctic cyclones may be associated with periods of locally enhanced sea ice loss during the summer, and some studies have found that an intense cyclone in August 2012 resulted in a rapid sea ice retreat. This study uses a coupled atmosphere‐ocean‐ice model (Navy‐ESPC) to explore the relationship between the 2012 cyclone and short‐term sea ice melting. There are two mechanisms of cyclone‐induced melting in Navy‐ESPC: turbulent mixing of a warm layer located at 15‐ to 35‐m depth increases bottom melting and warm air advection by the strong surface winds increases surface melting. Although the rate of sea ice melt is substantially increased in association with the cyclone, this effect is confined to a relatively small region and only lasts for a few days. There is no clear signature of the cyclone on the overall Arctic sea ice extent in Navy‐ESPC
Electrically tunable detector of THz-frequency signals based on an antiferromagnet
A concept of an electrically tunable resonance detector of THz-frequency
signals based on antiferromagnetic/heavy metal (AFM/HM) hetero-structure is
proposed. The conversion of a THz-frequency input signal into DC voltage is
done using the inverse spin Hall effect in an (AFM/HM) bilayer. An additional
bias DC current in the HM layer can be used to vary the effective anisotropy of
the AFM, and, therefore, to tune the AFMR frequency. The proposed AFM/HM
hetero-structure works as a resonance-type quadratic detector which can be
tuned by the bias current in the range of at least 10 percent of the AFMR
frequency and our estimations show that the sensitivity of this detector could
be comparable to that of modern detectors based on the Schottky, Gunn or
graphene-based diodes
Scalable synchronization of spin-Hall oscillators in out-of-plane field
A strategy for a scalable synchronization of an array of spin-Hall
oscillators (SHOs) is illustrated. In detail, we present micromagnetic
simulations of two and five SHOs realized by means of couples of triangular
golden contacts on the top of a Pt/CoFeB/Ta trilayer. Results highlight that
the synchronization occurs for the whole current region that gives rise to the
excitation of self-oscillations. This is linked to the role of the
magnetodipolar coupling, which is the phenomenon driving the synchronization
when the distance between oscillators is not too large. Synchronization turns
out to be also robust against geometrical differences of the contacts,
simulated by considering variable distances between the tips ranging from 100nm
to 200nm. Besides, it entails an enlargement of the radiation pattern that can
be useful for the generation of spin-waves in magnonics applications.
Simulations performed to study the effect of the interfacial
Dzyaloshinskii-Moriya interaction show nonreciprocity in spatial propagation of
the synchronized spin-wave. The simplicity of the geometry and the robustness
of the achieved synchronization make this design of array of SHOs scalable for
a larger number of synchronized oscillators
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