162 research outputs found
Enhanced exchange bias in MnN/CoFe bilayers after high-temperature annealing
We report an exchange bias of more than Oe at room temperature in
MnN/CoFe bilayers after high-temperature annealing. We studied the dependence
of exchange bias on the annealing temperature for different MnN thicknesses in
detail and found that samples with nm show an increase of
exchange bias for annealing temperatures higher than
T_{\text{A}}=400\,^{\circ}C. Maximum exchange bias values exceeding
Oe with reasonably small coercive fields around Oe are achieved
for nm. The median blocking temperature of those
systems is determined to be 180\,^{\circ}C after initial annealing at
T_{\text{A}}=525\,^{\circ}C. X-ray diffraction measurements and Auger depth
profiling show that the large increase of exchange bias after high-temperature
annealing is accompanied by strong nitrogen diffusion into the Ta buffer layer
of the stacks
Influence of tetragonal distortion on the magnetic and electronic properties of the Heusler compound Co2TiSn from first principles
Using the full potential linearized augmented plane wave plus local orbitals
method we determine ab-initio the lattice parameters of tetragonally distorted
Co2TiSn in the L21 structure. The tetragonal lattice parameter c is determined
as a function of the lattice parameter a by energy minimization. The change in
total energy is found to be only a few with respect to room
temperature. The spin polarizations as well as the magnetizations are stable
against small lattice distortions. It is shown, that the volume is not constant
upon distortion and that the volume change is related with significant changes
in the magnetization and the gap energy.Comment: 3 pages, 4 figure
Ab initio prediction of ferrimagnetism, exchange interactions and Curie temperatures in Mn2TiZ Heusler compounds
The Heusler compounds MnTiZ (Z = Al, Ga, In, Si, Ge, Sn, P, As, Sb) are
of large interest due to their potential ferrimagnetic properties and high spin
polarization. Here, we present calculations of the structural and magnetic
properties of these materials. Their magnetic moment follows the Slater-Pauling
rule . None of them is actually a perfect half-metallic
ferrimagnet, but some exhibit more than 90% spin polarization and Curie
temperatures well above room temperature. The exchange interactions are
complex, direct and indirect exchange contributions are identified. The Curie
temperature scales with the total magnetic moment, and it has a positive
pressure dependence. The role of the Z element is investigated: it influences
the properties of the compounds mainly via its valence electron number and its
atomic radius, which determines the lattice parameter. Based on these results,
MnTiSi, MnTiGe, and MnTiSn are proposed as candidates for
spintronic applications.Comment: 13 pages, 6 figure
Exchange interactions and Curie temperatures in Mn2CoZ compounds
The generalized Heusler compounds Mn2CoZ (Z = Al, Ga, In, Si, Ge, Sn, Sb)
with the Hg2CuTi structure are of large interest due to their half-metallic
ferrimagnetism. The complex magnetic interactions between the constituents are
studied by first principles calculations of the Heisenberg exchange coupling
parameters, and Curie temperatures are calculated from those. Due to the direct
Mn-Mn exchange interaction in Mn2CoZ, the Curie temperature decreases, while
the total moment increases when changing Z from one group to another. The
exchange interactions are dominated by a strong direct exchange between Co and
its nearest neighbor Mn on the B site, which is nearly constant. The coupling
between the nearest-neighbor Mn atoms scales with the magnetic moment of the Mn
atom on the C site. Calculations with different lattice parameters suggest a
negative pressure dependence of the Curie temperature, which follows from
decreasing magnetic moments. Curie temperatures of more than 800 K are
predicted for Mn2CoAl (890 K), Mn2CoGa (886 K), and Mn2CoIn (845 K).Comment: 12 pages, 3 figure
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
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