28 research outputs found
Theory of the magnetoeletric effect in a lightly doped high-Tc cuprate
In a recent study Viskadourakis et al. discovered that extremely underdoped
La_2CuO_(4+x) is a relaxor ferroelectric and a magnetoelectric material at low
temperatures. It is further observed that the magnetoelectric response is
anisotropic for different directions of electric polarization and applied
magnetic field. By constructing an appropriate Landau theory, we show that a
bi-quadratic magnetoelectric coupling can explain the experimentally observed
polarization dependence on magnetic field. This coupling leads to several novel
low-temperature effects including a feedback enhancement of the magnetization
below the ferroelectric transition, and a predicted magnetocapacitive effect.Comment: 5 pages, 4 figure
Bi-quadratic magnetoelectric coupling in underdoped La_2CuO_{4+x}
The recent discovery of relaxor ferroelectricity and magnetoelectric effect
in lightly doped cuprate material La_2CuO_{4+x} has provided a number of
questions concerning its theoretical description. It has been argued using a
Ginzburg-Landau free energy approach that the magnetoelectric effect can be
explained by the presence of bi-quadratic interaction terms in the free energy.
Here, by using the same free energy functional, we study the variety of
behavior which can emerge in the electric polarization under an external
magnetic field. Subsequently, we discuss the role of Dzyaloshinskii-Moriya
interaction in generating this magnetoelectric response. This work is
particularly relevant for such relaxor systems where the material-dependent
parameters would be affected by changes in e.g. chemical doping or cooling
rate.Comment: 8 pages, 2 figures. arXiv admin note: text overlap with
arXiv:1112.152
Electromagnetic shielding effectiveness of 3D printed polymer composites
We report on preliminary results regarding the electromagnetic shielding effectiveness of various 3D printed polymeric composite structures. All studied samples were fabricated using 3D printing technology, following the fused deposition modeling approach, using commercially available filaments as starting materials. The electromagnetic shielding performance of the fabricated 3D samples was investigated in the so called C-band of the electromagnetic spectrum (3.5–7.0 GHz), which is typically used for long-distance radio telecommunications. We provide evidence that 3D printing technology can be effectively utilized to prepare operational shields, making them promising candidates for electromagnetic shielding applications for electronic devices
Negative Giant Longitudinal Magnetoresistance in NiMnSb/InSb: An interface effect
We report on the electrical and magneto-transport properties of the contact
formed between polycrystalline NiMnSb thin films grown using pulsed laser
deposition (PLD) and n-type degenerate InSb (100) substrates. A negative giant
magnetoresistance (GMR) effect is observed when the external magnetic field is
parallel to the surface of the film and to the current direction. We attribute
the observed phenomenon to magnetic precipitates formed during the magnetic
film deposition and confined to a narrow layer at the interface. The effect of
these precipitates on the magnetoresistance depends on the thermal processing
of the system.Comment: 14 pages, 4 figure
Ferroelectricity in underdoped La-based cuprates
Doping a parent antiferromagnetic Mott insulator in cuprates leads to
short-range electronic correlations and eventually to high-Tc
superconductivity. However, the nature of charge correlations in the lightly
doped cuprates remains unclear. Understanding the intermediate electronic phase
in the phase diagram (between the parent insulator and the high-Tc
superconductor) is expected to elucidate the complexity both inside and outside
the superconducting dome, and in particular in the underdoped region. One such
phase is ferroelectricity whose origin and relation to the properties of
high-Tc superconductors is subject of current research. Here we demonstrate
that ferroelectricity and the associated magnetoelectric coupling are in fact
common in La-214 cuprates namely, LaSrCuO,
LaLiCuO and LaCuO. It is proposed that
ferroelectricity results from local CuO octahedral distortions, associated
with the dopant atoms and/or clustering of the doped charge carriers, which
break spatial inversion symmetry at the local scale whereas magnetoelectric
coupling can be tuned through Dzyaloshinskii-Moriya interaction.Comment: 13 pages, 12 figure
Geometric tuning of charge and spin correlations in manganite superlattices
We report a modulation of the in-plane magnetotransport in artificial
manganite superlattice (SL) [(NdMnO3)n /(SrMnO3)n /(LaMnO3)n]m by varying the
layer thickness n while keeping the total thickness of the structure constant.
Charge transport in these heterostructures is confined to the interfaces and
occurs via variable range hopping (VRH). Upon increasing n, the interfacial
separation rises, leading to a suppression of the electrostatic screening
between carriers of neighboring interfaces and the opening of a Coulomb gap at
the Fermi level (EF). The high-field magnetoresistance (MR) is universally
negative due to progressive spin alignment. However at a critical thickness of
n=5 unit cells (u.c.), an exchange field coupling between ferromagnetically
ordered interfaces results in positive MR at low magnetic field (H). Our
results demonstrate the ability to geometrically tune the electrical transport
between regimes dominated by either charge or spin correlations.Comment: 19 pages, 5 Figures, accepted for publication in AP