68 research outputs found
Non-linear spin-wave excitation at low bias fields
Non-linear magnetization dynamics is essential for the operation of many
spintronics devices. For microwave assisted switching of magnetic elements the
low field regime is of particular interest. In addition a large number of
experiments uses high amplitude FMR in order to generate d.c. currents via spin
pumping mechanism. Here we use time resolved X-ray magnetic circular dichroism
experiments to determine the number density of excited magnons in magnetically
soft Ni_80Fe_20 thin films at small bias fields and large rf-excitation
amplitudes. Our data shows that the common model of non-linear ferromagnetic
resonance is not suitable to describe the low bias field limit. Here we derive
a new model of parametric spin-wave excitation which correctly predicts
threshold amplitudes and decay rates also at low bias fields. In fact a new
series of critical modes with amplitude phase oscillations is found,
generalizing the theory of parametric spin-wave excitation
Role of Spin Momentum Current in Magnetic Non-Local Damping of Ultrathin Film Structures
Non-local damping was investigated by Ferromagnetic Resonance (FMR) using ultrathin magnetic single and double layer structures prepared by Molecular Beam Epitaxy (MBE). The double layer structures show magnetic damping which is caused by spin transport across a normal metal spacer (N). In double layer structures a thin Fe layer, F1, was separated from a thick Fe layer, F2, by a Au(001) spacer. The interface magnetic anisotropies separated the FMR fields of F1 and F2 by a big margin allowing one to investigate FMR in F1 while F2 had a negligible angle of precession, and vice versa. The Fe films in magnetic double layers acquire non-local interface Gilbert damping. It will be shown that the precessing magnetic moments act as spin pumps and spin sinks. This concept was tested by investigating the FMR linewidth around an accidental crossover of the resonance fields for the layers F1 and F2. There is another possible mechanism for non-local damping which is based on a "breathing Fermi surface" of the spacer. The temperature dependence of the non-local damping indicates that this mechanism is weak in Au spacers. Surprisingly the Au spacer acts as an additional impedance for the spin pump mechanism. Finally, it will be shown that electron-electron correlations in a Pd spacer can lead to a significant enhancement of the non-local damping
Magnetic microstructure and magnetotransport in Co2FeAl Heusler compound thin films
We correlate simultaneously recorded magnetotransport and spatially resolved
magneto optical Kerr effect (MOKE) data in Co2FeAl Heusler compound thin films
micropatterned into Hall bars. Room temperature MOKE images reveal the
nucleation and propagation of domains in an externally applied magnetic field
and are used to extract a macrospin corresponding to the mean magnetization
direction in the Hall bar. The anisotropic magnetoresistance calculated using
this macrospin is in excellent agreement with magnetoresistance measurements.
This suggests that the magnetotransport in Heusler compounds can be adequately
simulated using simple macrospin models, while the magnetoresistance
contribution due to domain walls is of negligible importance
A Comprehensible Review: Magnonic Magnetoelectric Coupling in Ferroelectric/ Ferromagnetic Composites
Composite materials consisting of coupled magnetic and ferroelectric layers
hold the promise for new emergent properties such as controlling magnetism with
electric fields. Obviously, the interfacial coupling mechanism plays a crucial
role and its understanding is the key for exploiting this material class for
technological applications. This short review is focused on the magnonic-based
magnetoelectric coupling that forms at the interface of a metallic ferromagnet
with a ferroelectric insulator. After analyzing the physics behind this
coupling, the implication for the magnetic, transport, and optical properties
of these composite materials is discussed. Furthermore, examples for the
functionality of such interfaces are illustrated by the electric field
controlled transport through ferroelectric/ferromagnetic tunnel junctions, the
electrically and magnetically controlled optical properties, and the generation
of electromagnon solitons for the use as reliable information carriers.Comment: Physica Status Solidi B 1, 1900750 (2020
Modulating the polarization of broadband terahertz pulses from a spintronic emitter at rates up to 10 kHz
eliable modulation of terahertz electromagnetic waveforms is important for many applications. Here, we rapidly modulate the direction of the electric field of linearly polarized terahertz electromagnetic pulses with 1–30 THz bandwidth by applying time-dependent magnetic fields to a spintronic terahertz emitter. Polarity modulation of the terahertz field with more than 99% contrast at a rate of 10 kHz is achieved using a harmonic magnetic field. By adding a static magnetic field, we modulate the direction of the terahertz field between angles of, for instance, −53° and 53° at kilohertz rates. We believe our approach makes spintronic terahertz emitters a promising source for low-noise modulation spectroscopy and polarization-sensitive techniques such as ellipsometry at 1–30 THz
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