138 research outputs found
Electric field effects on magnetotransport properties of multiferroic Py/YMnO3/Pt heterostructures
We report on the exchange bias between antiferromagnetic and ferroelectric
hexagonal YMnO3 epitaxial thin films sandwiched between a metallic electrode
(Pt) and a soft ferromagnetic layer (Py). Anisotropic magnetoresistance
measurements are performed to monitor the presence of an exchange bias field.
When the heteroestructure is biased by an electric field, it turns out that the
exchange bias field is suppressed. We discuss the dependence of the observed
effect on the amplitude and polarity of the electric field. Particular
attention is devoted to the role of current leakage across the ferroelectric
layer.Comment: Accepted for publication in Philosophical Magazine Letters (Special
issue on multiferroics
Strain-driven elastic and orbital-ordering effects on thickness-dependent properties of manganite thin films
We report on the structural and magnetic characterization of (110) and (001)
La2/3Ca1/3MnO3 (LCMO) epitaxial thin films simultaneously grown on (110) and
(001)SrTiO3 substrates, with thicknesses t varying between 8 nm and 150 nm. It
is found that while the in-plane interplanar distances of the (001) films are
strongly clamped to those of the substrate and the films remain strained up to
well above t=100 nm, the (110) films relax much earlier. Accurate determination
of the in-plane and out-of-plane interplanar distances has allowed concluding
that in all cases the unit cell volume of the manganite reduces gradually when
increasing thickness, approaching the bulk value. It is observed that the
magnetic properties (Curie temperature and saturation magnetization) of the
(110) films are significantly improved compared to those of (001) films. These
observations, combined with 55Mn-nuclear magnetic resonance data and X-ray
photoemission spectroscopy, signal that the depression of the magnetic
properties of the more strained (001)LCMO films is not caused by an elastic
deformation of the perovskite lattice but rather due to the electronic and
chemical phase separation caused by the substrate-induced strain. On the
contrary, the thickness dependence of the magnetic properties of the less
strained (110)LCMO films are simply described by the elastic deformation of the
manganite lattice. We will argue that the different behavior of (001) and
(110)LCMO films is a consequence of the dissimilar electronic structure of
these interfaces.Comment: 16 pages, 15 figure
Electric field control of exchange bias in multiferroic epitaxial heterostructures
The magnetic exchange bias between epitaxial thin films of the multiferroic
(antiferromagnetic and ferroelectric) hexagonal YMnO3 oxide and a soft
ferromagnetic (FM) layer is used to couple the magnetic response of the
ferromagnetic layer to the magnetic state of the antiferromagnetic one. We will
show that biasing the ferroelectric YMnO3 layer by an appropriate electric
field allows modifying and controlling the magnetic exchange bias and
subsequently the magnetotransport properties of the FM layer. This finding may
contribute to pave the way towards a new generation of electric-field
controlled spintronics devices.Comment: 15 pages, 5 figures, submitte
Pressure dependence of the Shubnikov-de Haas oscillation pectrum of beta''-(BEDT-TTF)4(NH4)[Cr(C2O4)3].DMF
The Shubnikov-de Haas (SdH) oscillation spectra of the
beta''-(BEDT-TTF)4(NH4)[Cr(C2O4)\_3].DMF organic metal have been studied in
pulsed magnetic fields of up to either 36 T at ambient pressure or 50 T under
hydrostatic pressures of up to 1 GPa. The ambient pressure SdH oscillation
spectra can be accounted for by up to six fundamental frequencies which points
to a rather complex Fermi surface (FS). A noticeable pressure-induced
modification of the FS topology is evidenced since the number of frequencies
observed in the spectra progressively decreases as the pressure increases.
Above 0.8 GPa, only three compensated orbits are observed, as it is the case
for several other isostructural salts of the same family at ambient pressure.
Contrary to other organic metals, of which the FS can be regarded as a network
of orbits, no frequency combinations are observed for the studied salt, likely
due to high magnetic breakdown gap values or (and) high disorder level
evidenced by Dingle temperatures as large as about 7 K.Comment: To be published in European Physical Journal
Indication for the coexistence of closed orbit and quantum interferometer with the same cross section in the organic metal (ET)4(H3O)[Fe(C2O4)3].C6H4Cl2: Persistence of SdH oscillations above 30 K
Shubnikov-de Haas (SdH) and de Haas-van Alphen (dHvA) oscillations spectra of
the quasi-two dimensional charge transfer salt
"-(ET)(HO)[Fe(CO)]CHCl have been
investigated in pulsed magnetic fields up to 54 T. The data reveal three basic
frequencies F, F and F, which can be interpreted on the basis
of three compensated closed orbits at low temperature. However a very weak
thermal damping of the Fourier component F, with the highest amplitude, is
evidenced for SdH spectra above about 6 K. As a result, magnetoresistance
oscillations are observed at temperatures higher than 30 K. This feature, which
is not observed for dHvA oscillations, is in line with quantum interference,
pointing to a Fermi surface reconstruction in this compound.Comment: published in Eur. Phys. J. B 71 203 (2009
Effect of band-filling and structural distortions on the Curie temperature of Fe-Mo double perovkites
By means of high resolution neutron powder diffraction at low temperature we
have characterized the structural details of
() and () series of compounds. This study reveals a similar variation of the mean
bond-angle \FeOMo in both series. In contrast, the mean bond-distance \FeMoO\
increases with La but not with Ca substitution. Both series also present a
different evolution of the Curie temperature (), which raises in the La
series and slightly decreases in the Ca one. We thus conclude that the
enhancement of in the La series is due to the electron filling of the
conduction band and a concomitant rising of the density of states at the Fermi
level.Comment: Revtex, 4 Journal pages, 2 figures, 1 tabl
Металографічний аналіз потенційних ділянок зародження руйнування зони термічного вливу низьковуглицевих сталей після лазерного зварювання
The work investigates the detection of dangerous areas of the zones of thermal impact on the basis of the research of welding joint structure formation after laser welding of low-carbon steels 09Mn2Si, 10CrNiCu, 10Mn2VNb. The complex of studies carried out showed that the welded joint is structurally divided into several zones. At the same time, metallographic analysis showed that in the zones of the welded joint there is a conglomerate of structures, which contains components characteristic both for metal in the cast state and for metal after accelerated cooling.Досліджено виявлення небезпечних ділянок зони термічного впливу на підставі дослідження формування структури зварного з'єднання після лазерного зварювання низьковуглецевих сталей 09Г2С, 10ХСНД, 10Г2ФБ. Проведений комплекс досліджень показав, що зварене з'єднання структурно розділити на кілька зон. При цьому, металографічний аналіз показав, що в зонах зварного з'єднання присутні конгломерат структур, який містить складові характерні як для металу в литому стані так і для металу після прискореного охолодження.Исследовано выявление опасных участков зоны термического влияния на основании исследования формирования структуры сварного соединения после лазерной сварки низкоуглеродистых сталей 09Г2С, 10ХСНД, 10Г2ФБ. Проведенный комплекс исследований показал, что сварное соединение структурно разделить на несколько зон. При этом, металлографический анализ показал, что в зонах сварного соединения присутствуют конгломерат структур, который содержит составляющие характерные как для металла в литом состоянии так и для металла после ускоренного охлаждения
Fermi surface and effect of high magnetic fields on the metal–semimetal Peierls-like transition of (TSeT)₂Cl
Resistance measurements in pulsed magnetic fields up to 55 T as well as a first-principles DFT calculation of the Fermi surface for the organic metal (TSeT)₂Cl have been performed to investigate its metal–semimetal phase transition. The results obtained are in line with the imperfect nesting that can be inferred from both the observed
metallic behavior of the resistivity at low temperature and the previously reported Shubnikov–de Haas oscillations due to small carrier pockets. The DFT study points out the possibility that the LUMO bands of the TSeT donor may interact with the HOMO ones and modify the shape of the Fermi surface under pressure
Strain-driven non-collinear magnetic ordering in orthorhombic epitaxial YMnO3 thin films
We show that using epitaxial strain and chemical pressure in orthorhombic
YMnO3 and Co-substituted (YMn0.95Co0.05O3) thin films, a ferromagnetic response
can be gradually introduced and tuned. These results, together with the
measured anisotropy of the magnetic response, indicate that the unexpected
observation of ferromagnetism in orthorhombic o-RMnO3 (R= Y, Ho, Tb, etc) films
originates from strain-driven breaking of the fully compensated magnetic
ordering by pushing magnetic moments away from the antiferromagnetic [010]
axis. We show that the resulting canting angle and the subsequent ferromagnetic
response, gradually increase (up to ~ 1.2\degree) by compression of the unit
cell. We will discuss the relevance of these findings, in connection to the
magnetoelectric response of orthorhombic manganites.Comment: Text + Figs Accepted in J. Appl. Phy
Slow oscillations of magnetoresistance in quasi-two-dimensional metals
Slow oscillations of the interlayer magnetoresistance observed in the layered
organic metal -(BEDT-TTF)IBr are shown to originate from the
slight warping of its Fermi surface rather than from independent small
cyclotron orbits. Unlike the usual Shubnikov-de Haas effect, these oscillations
are not affected by the temperature smearing of the Fermi distribution and can
therefore become dominant at high enough temperatures. We suggest that the slow
oscillations are a general feature of clean quasi-two-dimensional metals and
discuss possible applications of the phenomenon.Comment: 11 pages, 3 figure
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