214 research outputs found
Titanium Nitride as a Seed Layer for Heusler Compounds
Titanium nitride (TiN) shows low resistivity at room temperature, high
thermal stability and thus has the potential to serve as seed layer in magnetic
tunnel junctions. High quality TiN thin films with regard to the
crystallographic and electrical properties were grown and characterized by
X-ray diffraction and 4-terminal transport measurements. Element specific X-ray
absorption spectroscopy revealed pure TiN in the bulk. To investigate the
influence of a TiN seed layer on a ferro(i)magnetic bottom electrode, an
out-of-plane magnetized Mn2.45Ga as well as in- and out-of-plane magnetized
Co2FeAl thin films were deposited on a TiN buffer, respectively. The magnetic
properties were investigated using a superconducting quantum interference
device (SQUID) and anomalous Hall effect (AHE) for Mn2.45Ga. Magneto optical
Kerr effect (MOKE) measurements were carried out to investigate the magnetic
properties of Co2FeAl. TiN buffered Mn2.45Ga thin films showed higher
coercivity and squareness ratio compared to unbuffered samples. The Heusler
compound Co2FeAl showed already good crystallinity when grown at room
temperature
Defect-induced magnetism in graphite through neutron irradiation
We have investigated the variation in the magnetization of highly ordered
pyrolytic graphite (HOPG) after neutron irradiation, which introduces defects
in the bulk sample and consequently gives rise to a large magnetic signal. We
observe strong paramagnetism in HOPG, increasing with the neutron fluence. We
correlate the induced paramagnetism with structural defects by comparison with
density-functional theory calculations. In addition to the in-plane vacancies,
the trans-planar defects also contribute to the magnetization. The lack of any
magnetic order between the local moments is possibly due to the absence of
hydrogen/nitrogen chemisorption, or the magnetic order cannot be established at
all in the bulk form.Comment: 10 pages, 8 figure
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Anisotropic x ray magnetic linear dichroism - Its importance for the analysis of soft x ray spectra of magnetic oxides
Using spectroscopic information for x ray magnetometry and magnetic microscopy requires detailed theoretical understanding of spectral shape and magnitude of dichroism signals. We have shown unambiguously that--contrary to common belief--spectral shape and magnitude of x ray magnetic linear dichroism (XMLD) are not only determined by the relative orientation of magnetic moments and x ray polarization, but also their orientations relative to the crystallographic axes must be taken into account for accurate interpretation of XMLD data
Electronic structure of fully epitaxial Co2TiSn thin films
In this article we report on the properties of thin films of the full Heusler
compound Co2TiSn prepared by DC magnetron co-sputtering. Fully epitaxial,
stoichiometric films were obtained by deposition on MgO (001) substrates at
substrate temperatures above 600{\deg}C. The films are well ordered in the L21
structure, and the Curie temperature exceeds slightly the bulk value. They show
a significant, isotropic magnetoresistance and the resistivity becomes strongly
anomalous in the paramagnetic state. The films are weakly ferrimagnetic, with
nearly 1 \mu_B on the Co atoms, and a small antiparallel Ti moment, in
agreement with theoretical expectations. From comparison of x-ray absorption
spectra on the Co L3/L2 edges, including circular and linear magnetic
dichroism, with ab initio calculations of the x-ray absorption and circular
dichroism spectra we infer that the electronic structure of Co2TiSn has
essentially non-localized character. Spectral features that have not been
explained in detail before, are explained here in terms of the final state band
structure.Comment: 11 pages, 8 figure
Structural and magnetic properties of Co-Mn-Sb thin films
Thin Co-Mn-Sb films of different compositions were investigated and utilized
as electrodes in alumina based magnetic tunnel junctions with CoFe counter
electrode. The preparation conditions were optimized with respect to magnetic
and structural properties. The Co-Mn-Sb/Al-O interface was analyzed by X-ray
absorption spectroscopy and magnetic circular dichroism with particular focus
on the element-specific magnetic moments. Co-Mn-Sb crystallizes in different
complex cubic structures depending on its composition. The magnetic moments of
Co and Mn are ferromagnetically coupled in all cases. A tunnel magneto
resistance ratio of up to 24 % at 13K was found and indicates that Co-Mn-Sb is
not a ferromagnetic half-metal. These results are compared to recent works on
the structure and predictions of the electronic properties.Comment: 8 pages, 9 figure
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