50 research outputs found
Magnetic switching of nanoscale antidot lattices
We investigate the rich magnetic switching properties of nanoscale antidot lattices in the 200 nm regime. In-plane magnetized Fe, Co, and Permalloy (Py) as well as out-of-plane magnetized GdFe antidot films are prepared by a modified nanosphere lithography allowing for non-close packed voids in a magnetic film. We present a magnetometry protocol based on magneto-optical Kerr microscopy elucidating the switching modes using first-order reversal curves. The combination of various magnetometry and magnetic microscopy techniques as well as micromagnetic simulations delivers a thorough understanding of the switching modes. While part of the investigations has been published before, we summarize these results and add significant new insights in the magnetism of exchange-coupled antidot lattices.Web of Science775073
Ferromagnetic behaviour of ZnO: The role of grain boundaries
The possibility to attain ferromagnetic properties in transparent semiconductor oxides such as ZnO is very promising for future spintronic applications. We demonstrate in this review that ferromagnetism is not an intrinsic property of the ZnO crystalline lattice but is that of ZnO/ZnO grain boundaries. If a ZnO polycrystal contains enough grain boundaries, it can transform into the ferromagnetic state even without doping with “magnetic atoms” such as Mn, Co, Fe or Ni. However, such doping facilitates the appearance of ferromagnetism in ZnO. It increases the saturation magnetisation and decreases the critical amount of grain boundaries needed for FM. A drastic increase of the total solubility of dopants in ZnO with decreasing grain size has been also observed. It is explained by the multilayer grain boundary segregation
X-Ray Microscopy of Spin Wave Focusing using a Fresnel Zone Plate
Magnonics, i.e. the artificial manipulation of spin waves, is a flourishing
field of research with many potential uses in data processing within reach.
Apart from the technological applications the possibility to directly influence
and observe these types of waves is of great interest for fundamental research.
Guidance and steering of spin waves has been previously shown and lateral spin
wave confinement has been achieved. However, true spin wave focusing with both
lateral confinement and increase in amplitude has not been shown before. Here,
we show for the first time spin wave focusing by realizing a Fresnel zone plate
type lens. Using x-ray microscopy we are able to directly image the propagation
of spin waves into the nanometer sized focal spot. Furthermore, we observe that
the focal spot can be freely moved in a large area by small variations of the
bias field. Thus, this type of lens provides a steerable intense nanometer
sized spin wave source. Potentially, this could be used to selectively
illuminate magnonic devices like nano oscillators with a steerable spin wave
beam
Magnetic interlayer coupling between ferromagnetic SrRuO layers through a SrIrO spacer
A key element to tailor the properties of magnetic multilayers is the
coupling between the individual magnetic layers. In case of skyrmion hosting
multilayers, coupling of skyrmions across the magnetic layers is highly
desirable. Here the magnetic interlayer coupling was studied in epitaxial
all-oxide heterostructures of ferromagnetic perovskite SrRuO layers
separated by spacers of the strong spin-orbit coupling oxide SrIrO. This
combination of oxide layers is being discussed as a potential candidate system
to host N\'{e}el skyrmions. First order reversal curve (FORC) measurements were
performed in order to distinguish between magnetic switching processes of the
individual layers and to disentangle the signal of soft magnetic impurities
from the samples signal. Additionally, FORC investigations enabled to
determine whether the coupling between the magnetic layers is ferromagnetic or
antiferromagnetic. The observed interlayer coupling strength was weak for all
the heterostructures, with SrIrO spacers between 2 monolayers and 12
monolayers thick.Comment: 22 page
Ion beam lithography for Fresnel zone plates in X-ray microscopy
Fresnel Zone Plates (FZP) are to date very successful focusing optics for
X-rays. Established methods of fabrication are rather complex and based on
electron beam lithography (EBL). Here, we show that ion beam lithography (IBL)
may advantageously simplify their preparation. A FZP operable from the extreme
UV to the limit of the hard X-ray was prepared and tested from 450 eV to 1500
eV. The trapezoidal profile of the FZP favorably activates its 2nd order focus.
The FZP with an outermost zone width of 100 nm allows the visualization of
features down to 61, 31 and 21 nm in the 1st, 2nd and 3rd order focus
respectively. Measured efficiencies in the 1st and 2nd order of diffraction
reach the theoretical predictions
Orbital reflectometry
The occupation of d-orbitals controls the magnitude and anisotropy of the
inter-atomic electron transfer in transition metal oxides and hence exerts a
key influence on their chemical bonding and physical properties. Atomic-scale
modulations of the orbital occupation at surfaces and interfaces are believed
to be responsible for massive variations of the magnetic and transport
properties, but could thus far not be probed in a quantitative manner. Here we
show that it is possible to derive quantitative, spatially resolved orbital
polarization profiles from soft x-ray reflectivity data, without resorting to
model calculations. We demonstrate that the method is sensitive enough to
resolve differences of 3 % in the occupation of Ni e_g orbitals in adjacent
atomic layers of a LaNiO3-LaAlO3 superlattice, in good agreement with ab-initio
electronic-structure calculations. The possibility to quantitatively correlate
theory and experiment on the atomic scale opens up many new perspectives for
orbital physics in d-electron materials