457 research outputs found
Sinusoidal electromagnon in RMnO3: Indication of anomalous magnetoelectric coupling
The optical spectra in the family of multiferroic manganites RMnO3 is a great
puzzle. Current models can not explain the fact that two strong electromagnons
are present in the non-collinear spin cycloidal phase, with only one
electromagnon surviving the transition into the collinear spin sinusoidal
phase. We show that this is a signature of the presence of anomalous
magnetoelectric coupling that breaks rotational invariance in spin space and
generates oscillatory polarization in the ground state.Comment: 5 pages, 2 figure
Anisotropy study of multiferroicity in the pyroxene NaFeGeO
We present a study of the anisotropy of the dielectric, magnetic and
magnetoelastic properties of the multiferroic clinopyroxene NaFeGeO.
Pyroelectric currents, dielectric constants and magnetic susceptibilities as
well as the thermal expansion and the magnetostriction were examined on large
synthetic single crystals of NaFeGeO. The spontaneous electric
polarization detected below K in an
antiferromagnetically ordered state ( K) is mainly lying
within the plane with a small component along , indicating a triclinic
symmetry of the multiferroic phase of NaFeGeO. The electric
polarization can be strongly modified by applying magnetic fields along
different directions. We derive detailed magnetic-field versus temperature
phase diagrams and identify three multiferroic low-temperature phases, which
are separated by a non-ferroelectric, antiferromagnetically ordered state from
the paramagnetic high-temperature phase.Comment: 14 pages, 8 figures. (minor modifications and corrections of the
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EXPERIMENTAL STUDIES OF PRESSURE DISTRIBUTION IN TILTING PAD THRUST BEARING WITH SINGLE CONTINUOUS SURFACE PROFILED SECTOR SHAPED PADS
The effect of the film shape on the load carrying capacity of a hydrodynamically lubricated bearing has not been considered an important factor in the past. Flat faced tapered bearing and the Raileigh\u27s step bearing of constant film thickness have been the primary forms of film shapes for slider bearing studies and design data developments. There are indications in the literature that surface profiling/texturing can have significant and positive influence on the load carrying capacity of hydrodynamic pad thrust bearings. Therefore, the objective of this paper is to compare the experimental results of pressure temperature distributions in slider bearing with flat surface and with different single continuous surface profiled (Cycloidal,Catenoidal,Quadratic) sector shaped pads. Pressure results presented in this paper can provide a platform for validation of theoretical models. An experimental study has been performed to investigate the influence of single continuous surface profiled sector shaped pads in tilting pad thrust bearing. It has been found that with cycloidal shaped surface profiled sector shaped pads the pressure generated within fluid film is enhanced which in turn causes enhancement in load bearing capacity of hydrodynamic bearing
Spin-Hall magnetoresistance and spin Seebeck effect in spin-spiral and paramagnetic phases of multiferroic CoCr2O4 films
We report on the spin-Hall magnetoresistance (SMR) and spin Seebeck effect
(SSE) in multiferroic CoCr2O4 (CCO) spinel thin films with Pt contacts. We
observe a large enhancement of both signals below the spin-spiral (Ts = 28 K)
and the spin lock-in transitions (T_{lock_in} = 14 K). The SMR and SSE response
in the spin lock-in phase are one order of magnitude larger than those observed
at the ferrimagnetic transition temperature (Tc = 94 K), which indicates that
the interaction between spins at the Pt|CCO interface is more efficient in the
non-collinear magnetic state below Ts and T_{lock-in}. At T > Tc, magnetic
field-induced SMR and SSE signals are observed, which can be explained by a
high interface susceptibility. Our results show that the spin transport at the
Pt|CCO interface is sensitive to the magnetic phases but cannot be explained
solely by the bulk magnetization
Thickness-dependent magnetic structure of ultrathin Fe/Ir(001) films: from spin-spiral states towards ferromagnetic order
We present a detailed study of the ground-state magnetic structure of
ultrathin Fe films on the surface of fcc Ir(001). We use the spin-cluster
expansion technique in combination with the relativistic disordered local
moment scheme to obtain parameters of spin models and then determine the
favored magnetic structure of the system by means of a mean field approach and
atomistic spin dynamics simulations. For the case of a single monolayer of Fe
we find that layer relaxations very strongly influence the ground-state spin
configurations, whereas Dzyaloshinskii-Moriya (DM) interactions and biquadratic
couplings also have remarkable effects. To characterize the latter effect we
introduce and analyze spin collinearity maps of the system. While for two
monolayers of Fe we find a single-q spin spiral as ground state due to DM
interactions, for the case of four monolayers the system shows a noncollinear
spin structure with nonzero net magnetization. These findings are consistent
with experimental measurements indicating ferromagnetic order in films of four
monolayers and thicker.Comment: 9 pages, 7 figure
Dependence of electronic polarization on octahedral rotations in TbMnO3 from first principles
The electronic contribution to the magnetically induced polarization in
orthorhombic TbMnO3 is studied from first principles. We compare the cases in
which the spin cycloid, which induces the electric polarization via the
spin-orbit interaction, is in either the b-c or a-b plane. We find that the
electronic contribution is negligible in the first case, but much larger, and
comparable to the lattice-mediated contribution, in the second case. However,
we how that this behavior is an artifact of the particular pattern of
octahedral rotations characterizing the structurally relaxed Pbnm crystal
structure. To do so, we explore how the electronic contribution varies for a
structural model of rigidly rotated MnO6 octahedra, and demonstrate that it can
vary over a wide range, comparable with the lattice-mediated contribution, for
both b-c and a-b spirals. We introduce a phenomenological model that is capable
of describing this behavior in terms of sums of symmetry-constrained
contributions arising from the displacements of oxygen atoms from the centers
of the Mn-Mn bonds.Comment: 8 pages, 5 figures, 3 table
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