431 research outputs found
Epitaxial growth of metastable Pd(001) on bcc-Fe(001)
Epitaxial growth of metastable Pd(001) at high deposition temperatures up to a critical thickness of 6 monolayers on bcc-Fe(001) is reported, the critical thickness being depending dramatically on the deposition temperature. For larger thicknesses the Pd film undergoes a roughening transition with strain relaxation by forming a top polycrystalline layer. These results allow to make a correlation between previ-ously reported unusual magnetic properties of Fe/Pd double layers and the crystallographic structure of the Pd overlayer
Chemical potential of quasi-equilibrium magnon gas driven by pure spin current
We show experimentally that the spin current generated by the spin Hall
effect drives the magnon gas in a ferromagnet into a quasi-equilibrium state
that can be described by the Bose-Einstein statistics. The magnon population
function is characterized either by an increased effective chemical potential
or by a reduced effective temperature, depending on the spin current
polarization. In the former case, the chemical potential can closely approach,
at large driving currents, the lowest-energy magnon state, indicating the
possibility of spin current-driven Bose-Einstein condensation
Nanowire Spin Torque Oscillator Driven by Spin Orbit Torques
Spin torque from spin current applied to a nanoscale region of a ferromagnet
can act as negative magnetic damping and thereby excite self-oscillations of
its magnetization. In contrast, spin torque uniformly applied to the
magnetization of an extended ferromagnetic film does not generate
self-oscillatory magnetic dynamics but leads to reduction of the saturation
magnetization. Here we report studies of the effect of spin torque on a system
of intermediate dimensionality - a ferromagnetic nanowire. We observe coherent
self-oscillations of magnetization in a ferromagnetic nanowire serving as the
active region of a spin torque oscillator driven by spin orbit torques. Our
work demonstrates that magnetization self-oscillations can be excited in a
one-dimensional magnetic system and that dimensions of the active region of
spin torque oscillators can be extended beyond the nanometer length scale.Comment: The link to the published version is
http://www.nature.com/ncomms/2014/141205/ncomms6616/full/ncomms6616.htm
Microscopic theory of Bose–Einstein condensation of magnons at room temperature
A quantised spin wave – magnon – in magnetic films can undergo Bose- Einstein condensation into two energetically degenerate lowest-energy quan- tum states with non-zero wave vectors ±kBEC. This corresponds to two in- terfering condensates forming spontaneously in momentum space. Brillouin Light Scattering studies for a microwave-pumped film with sub-micrometer spatial resolution experimentally confirm the existence of the two wave- functions and show that their interference results in a non-uniform ground state of the condensate with the density oscillating in space. Moreover, fork dislocations in the density fringes provide direct experimental evidence for the formation of pinned half quantum vortices in the magnon condensate. The measured amplitude of the density oscillation implies the formation of a non-symmetric state that corresponds to non equal occupation of two en- ergy minima. We discuss the experimental findings and consider the theory of magnon condensates which includes, to leading order, the contribution from the non-condensed magnons. The e↵ect of the non-condensed magnon cloud is to increase the contrast of the asymmetric state and to bring about the experimental measurements
Faceting oscillations in nano-ferroelectrics
We observe periodic faceting of 8-nm diameter ferroelectric disks on a 10s time-scale when thin Pb(Zr0.52Ti0.48)O-3 film is exposed to constant high-resolution transmission electron microscopy beams. The oscillation is between circular disk geometry and sharply faceted hexagons. The behavior is analogous to that of spin structure and magnetic domain wall velocity oscillations in permalloy [Bisig et al., Nat. Commun. 4, 2328 (2013)], involving overshoot and de-pinning from defects [Amann et al., J. Rheol. 57, 149-175 (2013)]
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