35,603 research outputs found
Large Magneto-Dielectric Effects in Orthorhombic HoMnO3 and YMnO3
We have found a remarkable increase (up to 60 %) of the dielectric constant
with the onset of magnetic order at 42 K in the metastable orthorhombic
structures of YMnO3 and HoMnO3 that proves the existence of a strong
magneto-dielectric coupling in the compounds. Magnetic, dielectric, and
thermodynamic properties show distinct anomalies at the onset of the
incommensurate magnetic order and thermal hysteresis effects are observed
around the lock-in transition temperature at which the incommensurate magnetic
order locks into a temperature independent wave vector. The orders of Mn3+
spins and Ho3+ moments both contribute to the magneto-dielectric coupling. A
large magneto-dielectric effect was observed in HoMnO3 at low temperature where
the dielectric constant can be tuned by an external magnetic field resulting in
a decrease of up to 8 % at 7 Tesla. By comparing data for YMnO3 and HoMnO3 the
contributions to the coupling between the dielectric response and Mn and Ho
magnetic orders are separated.Comment: revised manuscrip
Site-dependent charge transfer at the Pt(111)-ZnPc interface and the effect of iodine
The electronic structure of ZnPc, from sub-monolayers to thick films, on bare
and iodated Pt(111) is studied by means of X-ray photoelectron spectroscopy
(XPS), X-ray absorption spectroscopy (XAS) and scanning tunneling microscopy
(STM). Our results suggest that at low coverage ZnPc lies almost parallel to
the Pt(111) substrate, in a non-planar configuration induced by Zn-Pt
attraction, leading to an inhomogeneous charge distribution within the molecule
and charge transfer to the molecule. ZnPc does not form a complete monolayer on
the Pt surface, due to a surface-mediated intermolecular repulsion. At higher
coverage ZnPc adopts a tilted geometry, due to a reduced molecule-substrate
interaction. Our photoemission results illustrate that ZnPc is practically
decoupled from Pt, already from the second layer. Pre-deposition of iodine on
Pt hinders the Zn-Pt attraction, leading to a non-distorted first layer ZnPc in
contact with Pt(111)-I or Pt(111)-I
, and a more homogeneous charge
distribution and charge transfer at the interface. On increased ZnPc thickness
iodine is dissolved in the organic film where it acts as an electron acceptor
dopant.Comment: 12 pages, 9 figure
Temperature dependence of electron-spin relaxation in a single InAs quantum dot at zero applied magnetic field
The temperature-dependent electron spin relaxation of positively charged
excitons in a single InAs quantum dot (QD) was measured by time-resolved
photoluminescence spectroscopy at zero applied magnetic fields. The
experimental results show that the electron-spin relaxation is clearly divided
into two different temperature regimes: (i) T < 50 K, spin relaxation depends
on the dynamical nuclear spin polarization (DNSP) and is approximately
temperature-independent, as predicted by Merkulov et al. (ii) T > about 50 K,
spin relaxation speeds up with increasing temperature. A model of two LO phonon
scattering process coupled with hyperfine interaction is proposed to account
for the accelerated electron spin relaxation at higher temperatures.Comment: 10 pages, 4 figure
Brueckner-Hartree-Fock and its renormalized calculations for finite nuclei
We have performed self-consistent Brueckner-Hartree-Fock (BHF) and its
renormalized theory to the structure calculations of finite nuclei. The
-matrix is calculated within the BHF basis, and the exact Pauli exclusion
operator is determined by the BHF spectrum. Self-consistent occupation
probabilities are included in the renormalized Brueckner-Hartree-Fock (RBHF).
Various systematics and convergences are studies. Good results are obtained for
the ground-state energy and radius. RBHF can give a more reasonable
single-particle spectrum and radius. We present a first benchmark calculation
with other {\it ab initio} methods using the same effective Hamiltonian. We
find that the BHF and RBHF results are in good agreement with other
methods
Nitrogen-induced magnetic transition in small chromium clusters
Using density functional theory with generalized gradient approximation for exchange and correlation, we show that otherwise antiferromagnetically coupled chromium atoms in very small chromium clusters couple ferromagnetically when doped with a nitrogen atom, thus leading to giant magnetic moments. For example, the magnetic moment of Cr2N is found to be 9ÎĽBwhile that of Cr2 is 0ÎĽB. Strong bonding between Cr and N atoms brings about this magnetic transition. The Cr atoms nearest neighbor to N couple ferromagnetically with each other and antiferromagnetically with nitrogen. The significance of these results in understanding the ferromagnetic order in Cr-doped GaN is discussed
- …