147 research outputs found
Robust coupling of superconducting order parameter in a mesoscale NbN-Fe-NbN epitaxial structure
We report an unconventional and promising route to self-assemble distributed
superconductor-ferromagnet-superconductor (S-F-S) Josephson Junctions on single
crystal [100] MgO. These structures consist of [110] epitaxial nano-plaquettes
of Fe covered with superconducting NbN films of varying thickness. The S-F-S
structures are characterized by strong magnetoresistance (MR) anisotropy for
the in-plane and out-of-plane magnetic fields. The stronger in-plane MR
suggests decoherence of S-F-S junctions whose critical current follows a
(1-T/Tc) and (1-T/Tc)1/2 dependence for T Tc and T<<Tc respectively, in
accordance with the theory of supercurrent transport in such junctions.Comment: 9 pages, 4 figure
Low-field microwave absorption in epitaxial La-Sr-Mn-O films resulting from the angle-tuned ferromagnetic resonance in the multidomain state
We studied magnetic-field induced microwave absorption in 100-200 nm thick
LaSrMnO films on SrTiO substrate and found a
low-field absorption with a very peculiar angular dependence: it appears only
in the oblique field and is absent both in the parallel and in the
perpendicular orientations. We demonstrate that this low-field absorption
results from the ferromagnetic resonance in the multidomain state (domain-mode
resonance). Its unusual angular dependence arises from the interplay between
the parallel component of the magnetic field that drives the film into
multidomain state and the perpendicular field component that controls the
domain width through its effect on domain wall energy. The low-field microwave
absorption in the multidomain state can be a tool to probe domain structure in
magnetic films with in-plane magnetization.Comment: 9 pages, 9 Figure
Spin wave resonances in La_{0.7}Sr_{0.3}MnO_{3} films: measurement of spin wave stiffness and anisotropy field
We studied magnetic field dependent microwave absorption in epitaxial
LaSrMnO films using an X-band Bruker ESR spectrometer. By
analyzing angular and temperature dependence of the ferromagnetic and spin-wave
resonances we determine spin-wave stiffness and anisotropy field. The spin-wave
stiffness as found from the spectrum of the standing spin-wave resonances in
thin films is in fair agreement with the results of inelastic neutron
scattering studies on a single crystal of the same composition [Vasiliu-Doloc
et al., J. Appl. Phys. \textbf{83}, 7343 (1998)].Comment: 15 pages, 7 figures (now figure captions are included
Carrier-induced ferromagnetism in n-type ZnMnAlO and ZnCoAlO thin films at room temperature
The realization of semiconductors that are ferromagnetic above room
temperature will potentially lead to a new generation of spintronic devices
with revolutionary electrical and optical properties. Transition temperatures
in doped ZnO are high but, particularly for Mn doping, the reported moments
have been small. We show that by careful control of both oxygen deficiency and
aluminium doping the ferromagnetic moments measured at room temperature in
n-type ZnMnO and ZnCoO are close to the ideal values of 5mB and 3mB
respectively. Furthermore a clear correlation between the magnetisation per
transition metal ion and the ratio of the number of carriers to the number of
transition metal donors was established as is expected for carrier induced
ferromagnetism for both the Mn and Co doped films. The dependence of the
magnetisation on carrier density is similar to that predicted for the
transition temperature for a dilute magnetic semiconductor in which the
exchange between the transition metal ions is through the free carriers.Comment: 14 pages pd
Nonresonant microwave absorption in epitaxial La-Sr-Mn-O films and its relation to colossal magnetoresistance
We study magnetic-field-dependent nonresonant microwave absorption and
dispersion in thin LaSrMnO films and show that it
originates from the colossal magnetoresistance. We develop the model for
magnetoresistance of a thin ferromagnetic film in oblique magnetic field. The
model accounts fairly well for our experimental findings, as well as for
results of other researchers. We demonstrate that nonresonant microwave
absorption is a powerful technique that allows contactless measurement of
magnetic properties of thin films, including magnetoresistance, anisotropy
field and coercive field.Comment: 20 pages, 11 figure
STM studies of electronic inhomogenieties in La_<SUB>{0.35}</SUB>Pr_<SUB>{0.275}</SUB>Ca_<SUB>{0.375}</SUB>MnO_<SUB>{3</SUB>} thin films
We report on temperature dependent STM/S measurements of Laser ablated epitaxial thin films ( ≅ 400nm thick) of La0:35Pr0:275Ca0:375MnO3 (LPCMO) on NdGaO3 (NGO) substrate. Four-probe resistivity measurement on this film shows a sharp transition near 145K (TMI ) and a significant hys- teresis with temperature between 90K and 160K. The topographic STM images show a clean terraced surface at all temperatures (77-350K) with mono-atomic steps and terrace width of 300-400nm. Some inhomogeni- eties are observed in the conductance images on a length scale of ≅20nm and more apparent near the terrace steps. Although spatial variations in spectra are seen at all temperatures but with some common features that evolve with temperature. The spectra become gap-like below 210K (i.e. TCO) and with cooling this charge-ordering (CO) gap becomes more pronounced with a magnitude of 0.4-0.5eV. This shows an increase in the strength of the CO order parameter and makes us believe that with cooling the CO fraction in the phase-separation scenario is not decreas- ing with temperature. In this case the large resistivity change at TMI may have to invoke a third phase (other than metallic and CO phases) that becomes metallic with cooling rather than CO fraction melting into metallic phase
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