95 research outputs found
Magnon-mediated spin current noise in ferromagnetnon-magnetic conductor hybrids
The quantum excitations of the collective magnetization dynamics in a
ferromagnet (F) - magnons - enable spin transport without an associated charge
current. This pure spin current can be transferred to electrons in an adjacent
non-magnetic conductor (N). We evaluate the finite temperature noise of the
magnon-mediated spin current injected into N by an adjacent F driven by a
coherent microwave field. We find that the dipolar interaction leads to
squeezing of the magnon modes giving them wavevector dependent non-integral
spin, which directly manifests itself in the shot noise. For temperatures
higher than the magnon gap, the thermal noise is dominated by large wavevector
magnons which exhibit negligible squeezing. The noise spectrum is white up to
the frequency corresponding to the maximum of the temperature or the magnon
gap. At larger frequencies, the noise is dominated by vacuum fluctuations. The
shot noise is found to be much larger than its thermal counterpart over a broad
temperature range, making the former easier to be measured experimentally
Super-Poissonian shot noise of squeezed-magnon mediated spin transport
The magnetization of a ferromagnet (F) driven out of equilibrium injects pure
spin current into an adjacent conductor (N). Such FN bilayers have become
basic building blocks in a wide variety of spin based devices. We evaluate the
shot noise of the spin current traversing the FN interface when F is
subjected to a coherent microwave drive. We find that the noise spectrum is
frequency independent up to the drive frequency, and increases linearly with
frequency thereafter. The low frequency noise indicates super-Poissonian spin
transfer, which results from quasi-particles with effective spin . For typical ferromagnetic thin films, is
related to the dipolar interaction-mediated squeezing of F eigenmodes.Comment: 4 pages, 2 figure
Spin pumping and shot noise in ferrimagnets: bridging ferro- and antiferromagnets
A combination of novel technological and fundamental physics prospects has
sparked a huge interest in pure spin transport in magnets, starting with
ferromagnets and spreading to antiferro- and ferrimagnets. We present a
theoretical study of spin transport across a ferrimagnetnon-magnetic
conductor interface, when a magnetic eigenmode is driven into a coherent state.
The obtained spin current expression includes intra- as well as
cross-sublattice terms, both of which are essential for a quantitative
understanding of spin-pumping. The dc current is found to be sensitive to the
asymmetry in interfacial coupling between the two sublattice magnetizations and
the mobile electrons, especially for antiferromagnets. We further find that the
concomitant shot noise provides a useful tool for probing the quasiparticle
spin and interfacial coupling.Comment: 4 pages + supplementary materia
Using superconductivity to control magnetism: a facet of superconducting spintronics
Magnets are used in electronics to store and read information. A magnetic
moment is rotated to a desired direction, so that information can later be
retrieved by reading this orientation. Controlling the moment via electric
currents causes resistive losses and heating, a major bottleneck in advancing
computing technologies. Superconducting spintronics can resolve this using the
unique features of superconductors.Comment: Feature in Europhysics News (4 pages
Enhancement of superconductivity mediated by antiferromagnetic squeezed magnons
We investigate theoretically magnon-mediated superconductivity in a
heterostructure consisting of a normal metal and a two-sublattice
antiferromagnetic insulator. The attractive electron-electron pairing
interaction is caused by an interfacial exchange coupling with magnons residing
in the antiferromagnet, resulting in p-wave, spin-triplet superconductivity in
the normal metal. Our main finding is that one may significantly enhance the
superconducting critical temperature by coupling the normal metal to only one
of the two antiferromagnetic sublattices employing, for example, an
uncompensated interface. Employing realistic material parameters, the critical
temperature increases from vanishingly small values to values significantly
larger than 1 K as the interfacial coupling becomes strongly
sublattice-asymmetric. We provide a general physical picture of this
enhancement mechanism based on the notion of squeezed bosonic eigenmodes.Comment: 15 pages, 4 figure
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
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