289 research outputs found
Strain Induced Vortex Core Switching in Planar Magnetostrictive Nanostructures
The dynamics of magnetic vortex cores is of great interest because the gyrotropic mode has applications in spin torque driven magnetic microwave oscillators, and also provides a means to flip the direction of the core for use in magnetic storage devices. Here, we propose a new means of stimulating magnetization reversal of the vortex core by applying a time-varying strain gradient to planar structures of the magnetostrictive material Fe81Ga19 (Galfenol), coupled to an underlying piezoelectric layer. Using micromagnetic simulations we have shown that the vortex core state can be deterministically reversed by electric field control of the time-dependent strain-induced anisotropy
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Chromium nanostructures formed by dewetting of heteroepitaxial films on W(100)
In this paper, we report the surprising formation of square-based facetted islands with linear dimension of the order of 500 nm upon dewetting of a Cr multilayer onW(100).We show that these square islands are composed of
inclined facets surrounding a depressed center such that the facet slopes inward with the outer edges of the islands
thicker than the centers. The islands’ shapes do not represent traditional equilibrium crystal shapes as expected
for a Wulf construction. In situ UV and x-ray photoelectron emission microscopy allied to spatially resolved
spectroscopy throws considerable light on the nature of the dewetting and shows that the metal surface between
the islands remains covered by a thin pseudomorphic wetting layer of ∼1 ML. Low-energy electron diffraction
and scanning tunneling and atomic force microscopies allow quantification of facet slopes, and we identify a
predominance of tilted Cr(100) facets ±5◦ off of the substrate normal bound by (210) planes at ∼26◦. The
epitaxial Cr islands adopt the bulk Cr lattice constant but are tilted with respect to the surface normal.We suggest
that the Cr crystallite tilting creates a vicinal-like interface structure that determines the island morpholog
Ultrafast changes of magnetic anisotropy driven by laser-generated coherent and noncoherent phonons in metallic films
Ultrafast optical excitation of a metal ferromagnetic film results in a modification of the magnetocrystalline anisotropy and induces the magnetization precession. We consider two main contributions to these processes: an effect of noncoherent phonons, which modifies the temperature dependent parameters of the magnetocrystalline anisotropy and coherent phonons in the form of a strain contributing via inverse magnetostriction. Contrary to earlier experiments with high-symmetry ferromagnetic structures, where these mechanisms could not be separated, we study the magnetization response to femtosecond optical pulses in the low-symmetry magnetostrictive galfenol film so that it is possible to separate the coherent and noncoherent phonon contributions. By choosing certain experimental geometry and external magnetic fields, we can distinguish the contribution from a specific mechanism. Theoretical analysis and numerical calculations are used to support the experimental observations and proposed model
Confined magnon dispersion in ferromagnetic and antiferromagnetic thin films in a second quantization approach: the case of Fe and NiO
We present a methodology based on the calculation of the inelastic scattering
from magnons via the spin scattering function in confined geometries such as
thin films using a second quantization formalism, for both ferromagnetic and
antiferromagnetic materials. The case studies are chosen with an aim to
demonstrate the effects of film thickness and crystal orientation on magnon
modes, using bcc Fe(100) and NiO with (100) and (111) crystallographic
orientations as prototypical systems. Due to the quantization of the
quasi-momentum we observe a granularity in the inelastic spectra in the
reciprocal space path reflecting the orientation of the thin film. This
approach also allows to capture softer modes that appear due to the partial
interaction of magnetic moments close to the surface in a thin film geometry,
in addition to bulk modes. The softer modes are also affected by
crystallographic orientations as illustrated by the different surface-related
peaks of NiO magnon density of states at approximately ~ 65 meV for (100) and ~
42 meV for (111). Additionally, we explore the role of anisotropy on magnon
modes, revealing that introducing anisotropy to both Fe and NiO films increases
the overall hardness of the magnon modes. The introduction of a surface
anisotropy produces a shift of the surface-related magnon DOS peak to higher
energies with increased surface anisotropy, and in some cases leading to
surface confined mode
Enhanced magnetoelectric effect in M-type hexaferrites by Co substitution into trigonal bi-pyramidal sites
The magnetoelectric effect in M-type Ti-Co doped strontium hexaferrite has been studied using a combination of magnetometry and element specific soft X-ray spectroscopies. A large increase (>×30) in the magnetoelectric coefficient is found when Co2+ enters the trigonal bi-pyramidal site. The 5-fold trigonal bi-pyramidal site has been shown to provide an unusual mechanism for electric polarization based on the displacement of magnetic transition metal (TM) ions. For Co entering this site, an off-centre displacement of the cation may induce a large local electric dipole as well as providing an increased magnetostriction enhancing the magnetoelectric effect
Enhanced magnetoelectric effect in M-type hexaferrites by Co substitution into trigonal bi-pyramidal sites
The magnetoelectric effect in M-type Ti-Co doped strontium hexaferrite has been studied using a combination of magnetometry and element specific soft X-ray spectroscopies. A large increase (>×30) in the magnetoelectric coefficient is found when Co2+ enters the trigonal bi-pyramidal site. The 5-fold trigonal bi-pyramidal site has been shown to provide an unusual mechanism for electric polarization based on the displacement of magnetic transition metal (TM) ions. For Co entering this site, an off-centre displacement of the cation may induce a large local electric dipole as well as providing an increased magnetostriction enhancing the magnetoelectric effect
Theory of momentum-resolved magnon electron energy loss spectra: The case of Yttrium Iron Garnet
We explore the inelastic spectra of electrons impinging in a magnetic system.
The methodology here presented is intended to highlight the charge-dependent
interaction of the electron beam in a STEM-EELS experiment, and the local
vector potential generated by the magnetic lattice. This interaction shows an
intensity smaller than the purely spin interaction, which is taken to
be functionally the same as in the inelastic neutron experiment. On the other
hand, it shows a strong scattering vector dependence () and a
dependence with the relative orientation between the probe wavevector and the
local magnetic moments of the solid. We present YIG as a case study due to its
high interest by the community
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