283 research outputs found
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
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
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
Temperature and bias voltage dependence of Co/Pd multilayer-based magnetic tunnel junctions with perpendicular magnetic anisotropy
Temperature- and bias voltage-dependent transport measurements of magnetic
tunnel junctions (MTJs) with perpendicularly magnetized Co/Pd electrodes are
presented. Magnetization measurements of the Co/Pd multilayers are performed to
characterize the electrodes. The effects of the Co layer thickness in the Co/Pd
bilayers, the annealing temperature, the Co thickness at the MgO barrier
interface, and the number of bilayers on the tunneling magneto resistance (TMR)
effect are investigated. TMR-ratios of about 11 % at room temperature and 18.5
% at 13 K are measured and two well-defined switching fields are observed. The
results are compared to measurements of MTJs with Co-Fe-B electrodes and
in-plane anisotropy
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
- …