383 research outputs found
Heat Flow Experiment engineering model 1 & 2 testing sequence
This ATM has been prepared to summarize the several sequences of experiment testing as they are presently defined for engineering model 1 & 2 and probe brassboard only.prepared by R. F. Kuschel
Role of NiO in the nonlocal spin transport through thin NiO films on Y3Fe5 O12
In spin-transport experiments with spin currents propagating through an antiferromagnetic (AFM) material, the antiferromagnet is mainly treated as a passive spin conductor not generating nor adding any spin current to the system. The spin current transmissivity of the AFM NiO is affected by magnetic fluctuations, peaking at the NĂ©el temperature and decreasing by lowering the temperature. To study the role of antiferromagnetism in local and nonlocal spin-transport experiments, we send spin currents through NiO of various thicknesses placed on Y3Fe5O12. The spin currents are injected either electrically or by thermal gradients and measured at a wide range of temperatures and magnetic field strengths. The transmissive role is reflected in the sign change of the local electrically injected signals and the decrease in signal strength of all other signals by lowering the temperature. The thermally generated signals, however, show an additional upturn below 100K that is unaffected by an increased NiO thickness. A change in the thermal conductivity could affect these signals. The temperature and magnetic field dependence are similar to those for bulk NiO, indicating that NiO itself contributes to thermally induced spin currents
Electronic and magnetic structure of epitaxial NiO/FeO(001) heterostructures grown on MgO(001) and Nb-doped SrTiO(001)
We study the underlying chemical, electronic and magnetic properties of a
number of magnetite based thin films. The main focus is placed onto
NiO/FeO(001) bilayers grown on MgO(001) and Nb-SrTiO(001)
substrates. We compare the results with those obtained on pure FeO(001)
thin films. It is found that the magnetite layers are oxidized and Fe
dominates at the surfaces due to maghemite (-FeO) formation,
which decreases with increasing magnetite layer thickness. From a layer
thickness of around 20 nm on the cationic distribution is close to that of
stoichiometric FeO. At the interface between NiO and FeO we
find the Ni to be in a divalent valence state, with unambiguous spectral
features in the Ni 2p core level x-ray photoelectron spectra typical for NiO.
The formation of a significant NiFeO interlayer can be excluded by
means of XMCD. Magneto optical Kerr effect measurements reveal significant
higher coercive fields compared to magnetite thin films grown on MgO(001), and
a 45 rotated magnetic easy axis. We discuss the spin magnetic moments
of the magnetite layers and find that the moment increases with increasing thin
film thickness. At low thickness the NiO/FeO films grown on
Nb-SrTiO exhibits a significantly decreased spin magnetic moments. A
thickness of 20 nm or above leads to spin magnetic moments close to that of
bulk magnetite
Monolithic Al2O3 Xerogels with Hierarchical Mesoâ/Macropore System as Catalyst Supports for Methanation of CO<sub>2</sub>
Argon metastable dynamics in a filamentary jet micro-discharge at atmospheric pressure
Space and time resolved concentrations of Ar () metastable atoms at
the exit of an atmospheric pressure radio-frequency micro-plasma jet were
measured using tunable diode laser absorption spectroscopy. The discharge
features a coaxial geometry with a hollow capillary as an inner electrode and a
ceramic tube with metal ring as outer electrode. Absorption profiles of
metastable atoms as well as optical emission measurements reveal the dynamics
and the filamentary structure of the discharge. The average spatial
distribution of Ar metastables is characterized with and without a target in
front of the jet, showing that the target potential and therewith the electric
field distribution substantially changes the filaments' expansion. Together
with the detailed analysis of the ignition phase and the discharge's behavior
under pulsed operation, the results give an insight into the excitation and
de-excitation mechanisms
Magnetic order of Dy3+ and Fe3+ moments in antiferromagnetic DyFeO3 probed by spin Hall magnetoresistance and spin Seebeck effect
We report on spin Hall magnetoresistance (SMR) and spin Seebeck effect (SSE)
in single crystal of the rare-earth antiferromagnet DyFeO with a thin Pt
film contact. The angular shape and symmetry of the SMR at elevated
temperatures reflect the antiferromagnetic order of the Fe moments as
governed by the Zeeman energy, the magnetocrystalline anisotropy and the
Dzyaloshinskii-Moriya interaction. We interpret the observed linear dependence
of the signal on the magnetic field strength as evidence for field-induced
order of the Dy moments up to room temperature. At and below the Morin
temperature of 50K, the SMR monitors the spin-reorientation phase
transition of Fe spins. Below 23K, additional features emerge that
persist below 4K, the ordering temperature of the Dy magnetic
sublattice. We conclude that the combination of SMR and SSE is a simple and
efficient tool to study spin reorientation phase transitions and sublattice
magnetizations
From Fe3O4/NiO bilayers to NiFe2O4-like thin films through Ni interdiffusion
Ferrites with (inverse) spinel structure display a large variety of electronic and magnetic properties, making some of them interesting for potential applications in spintronics. We investigate the thermally induced interdiffusion of Ni ions out of NiO into FeO ultrathin films, resulting in off-stoichiometric nickel ferriteâlike thin layers. We synthesized epitaxial FeO bilayers on Nb-doped SrTiO(001) substrates by means of reactive molecular beam epitaxy. Subsequently, we performed an annealing cycle comprising three steps at temperatures of 400C, 600C, and 800C under an oxygen background atmosphere. We studied the changes of the chemical and electronic properties as result of each annealing step with help of hard x-ray photoelectron spectroscopy and found a rather homogeneous distribution of Ni and Fe cations throughout the entire film after the overall annealing cycle. For one sample we observed a cationic distribution close to that of the spinel ferrite NiFeO. Further evidence comes from low-energy electron diffraction patterns indicating a spinel-type structure at the surface after annealing. Site- and element-specific hysteresis loops performed by x-ray magnetic circular dichroism uncovered the antiferrimagnetic alignment between the octahedral coordinated Ni and Fe ions and the Fe ion in tetrahedral coordination. We find a quite low coercive field of 0.02 T, indicating a rather low defect concentration within the thin ferrite films
Quantitative comparison of the magnetic proximity effect in Pt detected by XRMR and XMCD
X-ray resonant magnetic reflectivity (XRMR) allows for the simultaneous
measurement of structural, optical and magnetooptic properties and depth
profiles of a variety of thin film samples. However, a same-beamtime
same-sample systematic quantitative comparison of the magnetic properties
observed with XRMR and x-ray magnetic circular dichroism (XMCD) is still
pending. Here, the XRMR results (Pt L absorption edge) for the magnetic
proximity effect in Pt deposited on the two different ferromagnetic materials
Fe and CoFe are compared with quantitatively analyzed XMCD
results. The obtained results are in very good quantitative agreement between
the absorption-based (XMCD) and reflectivity-based (XRMR) techniques taking
into account an ab initio calculated magnetooptic conversion factor for the
XRMR analysis. Thus, it is shown that XRMR provides quantitative reliable spin
depth profiles important for spintronic and spin caloritronic transport
phenomena at this type of magnetic interfaces.Comment: This article may be downloaded for personal use only. Any other use
requires prior permission of the author and AIP Publishing. This article
appeared in Appl. Phys. Lett. 118, 012407 (2021) and may be found at
https://aip.scitation.org/doi/abs/10.1063/5.003258
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