881 research outputs found
The magnetotransport properties of La0.7Sr0.3MnO3/BaTiO3 superlattices grown by pulsed laser deposition technique
We have investigated the magnetotransport properties of La0.7Sr0.3MnO3/BaTiO3
superlattices, grown on SrTiO3 substrate by pulsed laser deposition technique,
both with current-in-plane and current-perpendicular-to-the-plane directions.
Several features indicate the presence of magnetic inhomogeneities at the
interfaces which is independent of BaTiO3 layer thickness variation. First, the
magnetic property in the superlattices decreases. Second, a hysteresis in
magnetoresistance due to the relaxation of the resistive state is observed.
Third, a threshold under an applied magnetic field in the magnetoresistance is
seen. Such behaviors are in agreement with the phase separation scenario which
could be the possible reason for these magnetic inhomogeneities at the
interfaces. On the contrary, the magnetoresistance with the
current-perpendicular-to-the-plane direction is mostly attributed to the
tunneling effect along with the ordering of the spin at the interface. This
study confirms the importance of the interfaces in superlattices that can be
used to control novel physical properties in oxide materials.Comment: 12 pages, 4 figures, to be published in Jour. Appl. Phy
Direct observation of pinned/biased moments in magnetic superlattices
We report the \QTR{it}{pinned/biased} \QTR{it}{moment} in the superlattices
consisting of ferromagnetic (FM) SrRuO and antiferromgnetic (AFM)
SrMnO. This superlattice system shows anisotropy and oriented
pinning/biasing in the field-cooled (FC) hysteresis loop. The in-plane
cooling-field provides antiferromagnetic orientations while out-of-plane
cooling-field provides ferromagnetic orientations to the pinned/biased moments.
The spacer layer thickness, strength and orientation of magnetic field, cooling
field, and driving current influence the pinning strength. We propose that the
magnetic structure is a repetition of ()/ unit below a
critical field to explain its magnetic and transport properties. The transport
behavior is discussed using the spin-dependent conduction.Comment: to be published in Physical Review
Effect of strain on the electrical transport and magnetization of the epitaxial Pr0.5Ca0.5MnO3/La0.5Ca0.5MnO3/ Pr0.5Ca0.5MnO3 trilayer structures
Epitaxial trilayer structures consisting of two antifferomagnetic
charge/orbital order insulators Pr0.5Ca0.5MnO3 (PCMO) and La0.5Ca0.5MnO3 (LCMO)
are grown on (001)-oriented SrTiO3 and LaAlO3 substrates. In this trilayer
series, a thin film of LCMO with various thicknesses is sandwiched between the
two fixed thicknesses of PCMO. These samples show a Curie temperature with a
hysteretic field dependent magnetization at 10 K, although the individual
compounds are antiferromagnetic. The zero field electronic transport of all
samples on LAO shows thermally activated behavior, while the thermally
activated behavior is suppressed and a metal-like transport is appearing for
the samples on STO as the LCMO layer thickness increases above 10 unit cell. We
have discussed these magnetic and transport properties of the trilayer
structures on STO and LAO by the interfacial effect due to the stabilized CO
state and the vibration mode of Jahn-Teller distortion.Comment: To be pubslised in Phys. Rev.
Relations between structural distortions and transport properties in NdCaMnO strained thin films
Strained thin films of charge/orbital ordered (CO/OO)
(NCMO) with various thickness have grown on (100)-SrTiO and (100)-LaAlO
substrates, by using the Pulsed Laser Deposition (PLD) technique. The thickness
of the films influences drastically the transport properties. As the thickness
decreases, the CO transition increases while at the same time the
insulator-to-metal transition temperature decreases under application of a 7T
magnetic field. Clear relationships between the structural distortions and the
transport properties are established. They are explained on the basis of the
elongation and the compression of the Mn-O-Mn and Mn-O bond angles and
distances of the \QTR{it}{Pnma} structure, which modify the bandwidth and the
Jahn-Teller distortion in these materialsComment: 11 pages, 6 figures. to be published in Journal Physics: Condensed
Matte
Electronic structure and optical band gap of CoFe2O4 thin films
Electronic structure and optical band gap of CoFe2O4 thin films grown on
(001) oriented LaAlO3 have been investigated. Surprisingly, these films show
additional Raman modes at room temperature as compared to a bulk spinel
structure. The splitting of Raman modes is explained by considering the
short-range ordering of Co and Fe cations in octahedral site of spinel
structure. In addition, an expansion of band-gap is observed with the reduction
of film thickness, which is explained by the quantum size effect and misfit
dislocation. Such results provide interesting insights for the growth of spinel
phases.Comment: 15 pages, 5 figures, and 1 table; Accepted and to be
published/appeared in APL soo
Exchange coupling induced antiferromagnetic-ferromagnetic transition in superlattices
Superlattices built from two antiferromagnetic (AFM) charge/orbital order
compounds, and , have been
studied as the thickness of () varied. High
structural quality thin films were obtained on substrates using the
pulsed laser deposition technique. An antiferromagnetic-to-ferromagnetic
transition, in addition to an enhancement of the coercivity, are observed as
the layer thickness increases. The small shift in the origin of the
field-cooled hysteresis loop along the field axis indicates the presence of
ferromagnetic and antiferromagnetic phases in the superlattices. We attribute
these features to the AFM spin fluctuations at the
interfaces resulting from the
strain effects.Comment: To be published in Phys. Rev.
Current-induced metallic behavior in PrCaMnO thin films: competition between Joule heating and nonlinear conduction mechanism
Thin films of Pr0.5Ca0.5MnO3 manganites exhibiting charge/orbital-ordered
properties with colossal magnetoresistance have been synthesized by the pulsed
laser deposition technique on both (100)-SrTiO3 and (100)-LaAlO3 substrates.
The effects of current-induced metallic-behavior of the films are investigated
as a function of the temperature and the magnetic field. Calculations based on
a heat transfer model across the substrate, and our resistivity measurements
reveal effects of Joule heating on charge transport over certain ranges of
temperatures and magnetic fields. Our results also indicate that a nonlinear
conduction, which cannot be explained by homogeneous Joule heating of the film,
is observed when the material is less resistive (10-2 W.cm). The origin of this
behavior is explained with a model based on local thermal instabilities
associated with phase-separation mechanism and a change in the long range
charge-ordered state.Comment: To be published in Phys. Rev.
Magnetocapacitance effect in perovskite-superlattice based multiferroics
We report the structural and magnetoelectrical properties of
LaCaMnO/BaTiO perovskite superlattices grown on
(001)-oriented SrTiO by the pulsed laser deposition technique. Magnetic
hysteresis loops together with temperature dependent magnetic properties
exhibit well-defined coercivity and magnetic transition temperature (T)
\symbol{126}140 K. electrical studies of films show that the
magnetoresistance (MR) is dependent on the BaTiO thickness and negative
as high as 30% at 100K are observed. The electrical studies reveal
that the impedance and capacitance in these films vary with the applied
magnetic field due to the magnetoelectrical coupling in these structures - a
key feature of multiferroics. A negative magnetocapacitance value in the film
as high as 3% per tesla at 1kHz and 100K is demonstrated, opening the route for
designing novel functional materials.Comment: To be published in Applied Physics Letter
Electrical transport in the ferromagnetic state of manganites: Small-polaron metallic conduction at low temperatures
We report measurements of the resistivity in the ferromagnetic state of
epitaxial thin films of La_{1-x}Ca_{x}MnO_{3} and the low temperature specific
heat of a polycrystalline La_{0.8}Ca_{0.2}MnO_{3}. The resistivity below 100 K
can be well fitted by \rho - \rho_{o} = E \omega_{s}/sinh^{2}(\hbar
\omega_{s}/2k_{B}T) with \hbar \omega_{s}/k_{B} \simeq 100 K and E being a
constant. Such behavior is consistent with small-polaron coherent motion which
involves a relaxation due to a soft optical phonon mode. The specific heat data
also suggest the existence of such a phonon mode. The present results thus
provide evidence for small-polaron metallic conduction in the ferromagnetic
state of manganites.Comment: 4 pages, 4 figures, submitted to PR
Hysteresis in the electronic transport of V2O3 thin films: non-exponential kinetics and range scale of phase coexistence
The thermal hysteresis of the electronic transport properties were studied
for V2O3 thin films. The temporal evolution of the resistance shows the
out-of-equilibrium nature of this hysteresis with a very slow relaxation.
Partial cycles reveal not only a behavior consistent with phase coexistence,
but also the presence of spinodal temperatures which are largely separated. The
temperature spreading of phase coexistence is consistent with the bulk phase
diagram in the pressure-temperature plane, confirming that the film is
effectively under an effective pressure induced by the substrate.Comment: Accepted for publication in Europhysics Letter
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