239 research outputs found
ORIENTATED FePt NANOCRYSTALS DEPOSITED ON POROUS SILICON
FePt nanocrystals with L10 chemical order have high magnetic anisotropy. To form the hard magnetic L10 phase as prepared fcc FePt nanocrystals need to be heated to 600°C. We demonstrate that the morphology of chemically etched porous silicon (PS) substrates and the presence of a magnetic field during the annealing process (600 °C, 1 h) affect the particle arrangement and orientation. X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM) show the presence of the L10 ordered FePt particles (average diameter 15 nm) uniformly distributed on the substrate. The presence of perpendicular magnetic field during annealing increases the order parameter degree of L10 FePt NPs. These effects can be investigated from variations of the XRD peaks intensity ratio. Presence of magnetic field of 20mT in the perpendicular direction to the substrate surface increases the (001) peak intensity ratio with respect to (111) peak from 0.27 to 0.58. This effect is due to the superlattice formation at (001) direction
Characteristics of 5M modulated martensite in Ni-Mn-Ga magnetic shape memory alloys
The applicability of the magnetic shape memory effect in Ni-Mn-based martensitic Heusler alloys is closely related to the nature of the crystallographically modulated martensite phase in these materials. We study the properties of modulated phases as a function of temperature and composition in three magnetic shape memory alloys Ni 49.8Mn25.0Ga25.2, Ni 49.8Mn27.1Ga23.1 and Ni 49.5Mn28.6Ga21.9. The effect of substituting Ga for Mn leads to an anisotropic expansion of the lattice, where the b-parameter of the 5M modulated structure increases and the a and c-parameters decrease with increasing Ga concentration. The modulation vector is found to be both temperature and composition dependent. The size of the modulation vector corresponds to an incommensurate structure for Ni 49.8Mn25.0Ga25.2 at all temperatures. For the other samples the modulation is incommensurate at low temperatures but reaches a commensurate value of q ≈ 0.400 close to room temperature. The results show that commensurateness of the 5M modulated structure is a special case of incommensurate 5M at a particular temperature
Spin relaxation time dependence on optical pumping intensity in GaAs:Mn
We analyze the dependence of electron spin relaxation time on optical pumping intensity in a partially compensated acceptor semiconductor GaAs:Mn using analytic solutions for the kinetic equations of the charge carrier concentrations. Our results are applied to previous experimental data of spin-relaxation time vs. excitation power for magnetic concentrations of approximately 1017 cm-3 . The agreement of our analytic solutions with the experimental data supports the mechanism of the earlier-reported atypically long electron-spin relaxation time in the magnetic semiconductor
Magnetic phase transitions in Ta/CoFeB/MgO multilayers
We study thin films and magnetic tunnel junction nanopillars based on
Ta/CoFeB/MgO multilayers by electrical transport and
magnetometry measurements. These measurements suggest that an ultrathin
magnetic oxide layer forms at the CoFeB/MgO interface. At
approximately 160 K, the oxide undergoes a phase transition from an insulating
antiferromagnet at low temperatures to a conductive weak ferromagnet at high
temperatures. This interfacial magnetic oxide is expected to have significant
impact on the magnetic properties of CoFeB-based multilayers used in spin
torque memories
Inertial effects in ultrafast spin dynamics
The dynamics of magnetic moments consist of a precession around the magnetic
field direction and a relaxation towards the field to minimize the energy.
While the magnetic moment and the angular momentum are conventionally assumed
to be parallel to each other, at ultrafast time scales their directions become
separated due to inertial effects. The inertial dynamics give rise to
additional high-frequency modes in the excitation spectrum of magnetic
materials. Here, we review the recent theoretical and experimental advances in
this emerging topic and discuss the open challenges and opportunities in the
detection and the potential applications of inertial spin dynamics.Comment: 11 pages, 8 figure
Prediction of a surface state and a related surface insulator-metal transition for the (100) surface of stochiometric EuO
We calculate the temperature and layer-dependent electronic structure of a
20-layer EuO(100)-film using a combination of first-principles and model
calculation based on the ferromagnetic Kondo-lattice model. The results suggest
the existence of a EuO(100) surface state which can lead to a surface
insulator-metal transition.Comment: 9 pages, 5 figures, Phys. Rev. Lett. (in press
Crystallographically oriented Co and Ni nanocrystals inside ZnO formed by ion implantation and postannealing
In the last decade, transition-metal-doped ZnO has been intensively
investigated as a route to room-temperature diluted magnetic semiconductors
(DMSs). However, the origin for the reported ferromagnetism in ZnO-based DMS
remains questionable. Possible options are diluted magnetic semiconductors,
spinodal decomposition, or secondary phases. In order to clarify this question,
we have performed a thorough characterization of the structural and magnetic
properties of Co- and Ni-implanted ZnO single crystals. Our measurements reveal
that Co or Ni nanocrystals (NCs) are the major contribution of the measured
ferromagnetism. Already in the as-implanted samples, Co or Ni NCs have formed
and they exhibit superparamagnetic properties. The Co or Ni NCs are
crystallographically oriented with respect to the ZnO matrix. Their magnetic
properties, e.g., the anisotropy and the superparamagnetic blocking
temperature, can be tuned by annealing. We discuss the magnetic anisotropy of
Ni NCs embedded in ZnO concerning the strain anisotropy.Comment: 13 pages, 14 figure
Magnetic properties of carbon-coated permalloy films
This work is supported by the German-Russian Interdisciplinary Science Center (G-RISC) funded by the German Federal Foreign Office via the German Academic Exchange Service (DAAD)
Electron Spin Resonance of the ferromagnetic Kondo lattice CeRuPO
The spin dynamics of the ferromagnetic Kondo lattice CeRuPO is investigated
by Electron Spin Resonance (ESR) at microwave frequencies of 1, 9.4, and
34~GHz. The measured resonance can be ascribed to a rarely observed bulk Ce3+
resonance in a metallic Ce compound and can be followed below the ferromagnetic
transition temperature Tc=14 K. At T>Tc the interplay between the RKKY-exchange
interaction and the crystal electric field anisotropy determines the ESR
parameters. Near Tc the spin relaxation rate is influenced by the critical
fluctuations of the order parameter.Comment: This is an article accepted for publication in Journal of Physics:
Condensed Matte
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