33 research outputs found
Dephasing of Transverse Spin Current in Ferrimagnetic Alloys
It has been predicted that transverse spin current can propagate coherently
(without dephasing) over a long distance in antiferromagnetically ordered
metals. Here, we estimate the dephasing length of transverse spin current in
ferrimagnetic CoGd alloys by spin pumping measurements across the compensation
point. A modified drift-diffusion model, which accounts for spin-current
transmission through the ferrimagnet, reveals that the dephasing length is
about 4-5 times longer in nearly compensated CoGd than in ferromagnetic metals.
This finding suggests that antiferromagnetic order can mitigate spin dephasing
-- in a manner analogous to spin echo rephasing for nuclear and qubit spin
systems -- even in structurally disordered alloys at room temperature. We also
find evidence that transverse spin current interacts more strongly with the Co
sublattice than the Gd sublattice. Our results provide fundamental insights
into the interplay between spin current and antiferromagnetic order, which are
crucial for engineering spin torque effects in ferrimagnetic and
antiferromagnetic metals
Dynamic origin of the morphotropic phase boundary - Soft modes and phase instability in 0.68Pb(Mg1/3Nb2/3O3)-0.32PbTiO3
We report neutron inelastic scattering on single crystal
0.68Pb(Mg1/3Nb2/3O3)-0.32PbTiO3 (PMN-0.32PT), a relaxor ferroelectric material
that lies within the compositional range of the morphotropic phase boundary
(MPB). Data were obtained between 100 K and 600 K under zero and non-zero
electric field applied along the cubic [001] direction. The lowest energy,
zone-center, transverse optic phonon is strongly damped and softens slowly at
high temperature; however the square of the soft mode energy begins to increase
linearly with temperature as in a conventional ferroelectric, which we term the
soft mode "recovery," upon cooling into the tetragonal phase at TC. Our data
show that the soft mode in PMN-0.32PT behaves almost identically to that in
pure PMN, exhibiting the same temperature dependence and recovery temperature
even though PMN exhibits no well-defined structural transition (no TC). The
temperature dependence of the soft mode in PMN-0.32PT is also similar to that
in PMN-0.60PT; however in PMN-0.60PT the recovery temperature equals TC. These
results suggest that the temperature dependence and the energy scale of the
soft mode dynamics in PMN-xPT are independent of concentration on the Ti-poor
side of the MPB, but scale with TC for Ti-rich compositions. Thus the MPB may
be defined in lattice dynamical terms as the concentration where TC first
matches the recovery temperature of the soft mode. High-resolution x-ray
studies show that the cubic-to-ferroelectric phase boundary shifts to higher
temperatures by an abnormal amount within the MPB region in the presence of an
electric field. This suggests that an unusual instability exists within the
apparently cubic phase at the MPB.Comment: 13 pages, 6 figure
A low frequency mechanical transmitter based on magnetoelectric heterostructures operated at their resonance frequency
Magneto-elasto-electric (ME) coupling heterostructures, consisting of piezoelectric layers bonded to magnetostrictive ones, provide for a new class of electromagnetic emitter materials on which a portable (area ~ 16 cm 2 ) very low frequency (VLF) transmitter technology could be developed. The proposed ME transmitter functions as follows: (a) a piezoelectric layer is first driven by alternating current AC electric voltage at its electromechanical resonance (EMR) frequency, (b) subsequently, this EMR excites the magnetostrictive layers, giving rise to magnetization change, (c) in turn, the magnetization oscillations result in oscillating magnetic fields. By Maxwell’s equations, a corresponding electric field, is also generated, leading to electromagnetic field propagation. Our hybrid piezoelectric-magnetostrictive transformer can take an input electric voltage that may include modulation-signal over a carrier frequency and transmit via oscillating magnetic field or flux change. The prototype measurements reveal a magnetic dipole like near field, demonstrating its transmission capabilities. Furthermore, the developed prototype showed a 10 4 times higher efficiency over a small-circular loop of the same area, exhibiting its superiority over the class of traditional small antennas
Suppression of Spin Pumping at Metal Interfaces
An electrically conductive metal typically transmits or absorbs a spin
current. Here, we report on evidence that interfacing two metal thin films can
suppress spin transmission and absorption. We examine spin pumping in
ferromagnet/spacer/ferromagnet heterostructures, in which the spacer --
consisting of metallic Cu and Cr thin films -- separates the ferromagnetic
spin-source and spin-sink layers. The Cu/Cr spacer largely suppresses spin
pumping -- i.e., neither transmitting nor absorbing a significant amount of
spin current -- even though Cu or Cr alone transmits a sizable spin current.
The antiferromagnetism of Cr is not essential for the suppression of spin
pumping, as we observe similar suppression with Cu/V spacers where V is a
nonmagnetic analogue of Cr. We speculate that diverse combinations of
spin-transparent metals may form interfaces that suppress spin pumping,
although the underlying mechanism remains unclear. Our work may stimulate a new
perspective on understanding and engineering spin transport in metallic
multilayers
Magnetoelectricity in composites
Magnetoelectric composites, which simultaneously exhibit ferroelectricity and ferromagnetism, have recently stimulated a sharply increasing number of research activities for their scientific interest and significant technological promise in the novel multifunctional devices. Natural single-phase compounds are rare, and their magnetoelectric responses are either relatively weak or occurs at temperatures too low for practical applications. In contrast, composites, which incorporate both ferroelectric and ferri-/ferromagnetic phases, typically yield giant magnetoelectric coupling response above