302 research outputs found
Electric-field control of domain wall nucleation and pinning in a metallic ferromagnet
The electric (E) field control of magnetic properties opens the prospects of
an alternative to magnetic field or electric current activation to control
magnetization. Multilayers with perpendicular magnetic anisotropy (PMA) have
proven to be particularly sensitive to the influence of an E-field due to the
interfacial origin of their anisotropy. In these systems, E-field effects have
been recently applied to assist magnetization switching and control domain wall
(DW) velocity. Here we report on two new applications of the E-field in a
similar material : controlling DW nucleation and stopping DW propagation at the
edge of the electrode
Crystal-fields in YbInNi4 determined with magnetic form factor and inelastic neutron scattering
The magnetic form factor of YbInNi4 has been determined via the flipping
ratios R with polarized neutron diffraction and the scattering function S(Q,w)
was measured in an inelastic neutron scattering experiment. Both experiments
were performed with the aim to determine the crystal-field scheme. The magnetic
form factor clearly excludes the possibility of a \Gamma7 doublet as the ground
state. The inelastic neutron data exhibit two, almost equally strong peaks at
3.2 meV and 4.4 meV which points, in agreement with earlier neutron data,
towards a \Gamma8 quartet ground state. Further possibilities like a
quasi-quartet ground state are discussed.Comment: 7 pages, 5 figures, 2 tables, submitted to PR
Evolution of magnetic and microstructural properties of thick sputtered NdFeB films with processing temperature
Ta (100 nm) / NdFeB (5 m) / Ta (100 nm) films have been deposited onto
Si substrates using triode sputtering (deposition rate ~ 18 m/h). A 2-step
procedure was used : deposition at temperatures up to 400 C followed by ex-situ
annealing at higher temperatures. Post-deposition annealing temperatures above
650 C are needed to develop high values of coercivity. The duration of the
annealing time is more critical in anisotropic samples deposited onto heated
substrates than in isotropic samples deposited at lower temperatures. For a
given set of annealing conditions (750 C/ 10'), high heating rates (≥
2000 C / h) favour high coercivity in both isotropic and anisotropic films. The
shape and size of Nd2Fe14B grains depend strongly on the heating rate
Effect of H on the crystalline and magnetic structures of the YCo3-H(D) system. I. YCo3 from neutron powder diffraction and first-principles calculations
This paper reports investigations into the influence of hydrogen on the magnetic properties of the YCo3-H
system. We report results on the magnetic structure and magnetic transitions of YCo3 using a combination of
neutron powder diffraction measurements and first-principles full potential augmented plane wave + local
orbital calculations under the generalized gradient approximation. The ferromagnetic and ferrimagnetic structures
are examined on an equal footing. However, we identify that, no matter which structure is used as the
starting point, the neutron diffraction data always refines down to the ferrimagnetic structure with the Co2
atoms having antiparallel spins. In the ab initio calculations, the inclusion of spin-orbit coupling is found to be
important in the prediction of the correct magnetic ground state. Here, the results suggest that, for zero external
field and sufficiently low temperatures, the spin arrangement of YCo3 is ferrimagnetic rather than ferromagnetic
as previously believed. The fixed spin moment calculation technique has been employed to understand
the two successive field-induced magnetic transitions observed in previous magnetization measurements under
increasing ultrahigh magnetic fields. We find that the magnetic transitions start from the ferrimagnetic phase
�0.61�B/Co� and terminate with the ferromagnetic phase �1.16�B/Co�, while the spin on the Co2 atoms
progressively changes from antiparallel ferrimagnetic to paramagnetic and then to ferromagnetic. Our neutron
diffraction measurements, ab initio calculations, and the high field magnetization measurements are thus
entirely self-consistent
Why the iron magnetization in Gd2Fe14B and the spontaneous magnetization of Y2Fe14B depend on temperature differently
This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.It is demonstrated that the temperature dependence of the iron sublattice magnetization in Gd2Fe14B is affected significantly by the Gd-Fe exchange interaction. This is at variance with the common perception that MFe(T) in iron-rich rare-earth intermetallics is determined predominantly by the Fe-Fe exchange. This phenomenon is discussed by considering the modification of the low-energy spin-wave spectrum of Gd2Fe14B, as compared to that of Y2Fe14B, under the influence of the Gd-Fe interaction. The result is of particular significance for evaluating the temperature dependence of the magnetocrystalline anisotropy of iron or cobalt compounds with anisotropic rare earths (e.g., Nd2Fe14B) and in turn, of the hard magnetic properties of such compounds
A crystallographic phase transition within the magnetically ordered state of Ce_2Fe_17
X-ray diffraction experiments were performed on polycrystalline and
single-crystal specimens of CeFe at temperatures between 10 K and
300 K. Below = 1182 K, additional weak superstructure
reflections were observed in the antiferromagnetically ordered state. The
superstructure can be described by a doubling of the chemical unit cell along
the direction in hexagonal notation with the same space group as the room-temperature structure. The additional antiferromagnetic
satellite reflections observed in earlier neutron diffraction experiments can
be conclusively related to the appearance of this superstructure.Comment: 8 pages, figures, submitted for publication in Phys. Rev.
Theoretical Analysis of the "Double-q" Magnetic Structure of CeAl2
A model involving competing short-range isotropic Heisenberg interactions is
developed to explain the "double-q" magnetic structure of CeAl. For
suitably chosen interactions, terms in the Landau expansion quadratic in the
order parameters explain the condensation of incommensurate order at
wavevectors in the star of (1/2 , 1/2 , 1/2), where
is the cubic lattice constant. We show that the fourth order terms in the
Landau expansion lead to the formation of the so-called "double-q" magnetic
structure in which long-range order develops simultaneously at two
symmetry-related wavevectors, in striking agreement with the magnetic structure
determinations. Based on the value of the ordering temperature and of the
Curie-Weiss of the susceptibility, we estimate that the nearest
neighbor interaction is ferromagnetic, with K and the
next-nearest neighbor interaction is antiferromagnetic with K.
We also briefly comment on the analogous phenomenon seen in the similar system
TmS.Comment: 22 pages, 6 figure
Shell-driven magnetic stability in core-shell nanoparticles
The magnetic properties of ferromagnetic-antiferromagnetic Co-CoO core-shell nanoparticles are investigated as a function of the in-plane coverage density from 3.5% to 15%. The superparamagnetic blocking temperature, the coercivity, and the bias field radically increase with increasing coverage. This behavior cannot be attributed to the overall interactions between cores. Rather, it can be semiquantitatively understood by assuming that the shells of isolated core-shell nanoparticles have strongly degraded magnetic properties, which are rapidly recovered as nanoparticles come into contact
Electronic structure, magnetic and optical properties of intermetallic compounds R2Fe17 (R=Pr,Gd)
In this paper we report comprehensive experimental and theoretical
investigation of magnetic and electronic properties of the intermetallic
compounds Pr2Fe17 and Gd2Fe17. For the first time electronic structure of these
two systems was probed by optical measurements in the spectral range of 0.22-15
micrometers. On top of that charge carriers parameters (plasma frequency and
relaxation frequency) and optical conductivity s(w) were determined.
Self-consistent spin-resolved bandstructure calculations within the
conventional LSDA+U method were performed. Theoretical interpetation of the
experimental s(w) dispersions indicates transitions between 3d and 4p states of
Fe ions to be the biggest ones. Qualitatively the line shape of the theoretical
optical conductivity coincides well with our experimental data. Calculated by
LSDA+U method magnetic moments per formula unit are found to be in good
agreement with observed experimental values of saturation magnetization.Comment: 16 pages, 5 figures, 1 tabl
Observation of a Griffiths-like phase in the paramagnetic regime of ErCo_2
A systematic x-ray magnetic circular dichroism study of the paramagnetic
phase of ErCo2 has recently allowed to identify the inversion of the net
magnetization of the Co net moment with respect to the applied field well above
the ferrimagnetic ordering temperature, Tc. The study of small angle neutron
scattering measurements has also shown the presence of short range order
correlations in the same temperature region. This phenomenon, which we have
denoted parimagnetism, may be related with the onset of a Griffiths-like phase
in paramagnetic ErCo2. We have measured ac susceptibility on ErCo2 as a
function of temperature, applied field, and excitation frequency. Several
characteristics shared by systems showing a Griffiths phase are present in
ErCo2, namely the formation of ferromagnetic clusters in the disordered phase,
the loss of analyticity of the magnetic susceptibility and its extreme
sensitivity to an applied magnetic field. The paramagnetic susceptibility
allows to establish that the magnetic clusters are only formed by Co moments as
well as the intrinsic nature of those Co moments
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