5,100 research outputs found
Charge states and magnetic ordering in LaMnO3/SrTiO3 superlattices
We investigated the magnetic and optical properties of
[(LaMnO3)n/(SrTiO3)8]20 (n = 1, 2, and 8) superlattices grown by pulsed laser
deposition. We found a weak ferromagnetic and semiconducting state developed in
all superlattices. An analysis of the optical conductivity showed that the
LaMnO3 layers in the superlattices were slightly doped. The amount of doping
was almost identical regardless of the LaMnO3 layer thickness up to eight unit
cells, suggesting that the effect is not limited to the interface. On the other
hand, the magnetic ordering became less stable as the LaMnO3 layer thickness
decreased, probably due to a dimensional effect.Comment: 17 pages including 4 figures, accepted for publication in Phys. Rev.
Ground state, electronic structure and magnetism of LaMnO3
We have calculated the discrete low-energy electronic structure in LaMnO3
originating from the atomic-like states of the strongly correlated 3d4
electronic system occurring in the Mn3+ ion. We take into account very strong
intra-atomic correlations, crystal field interactions and the intra-atomic
spin-orbit coupling. We calculated magnetic and paramagnetic state of LaMnO3
within the consistent description given by Quantum Atomistic Solid State Theory
(QUASST). Our studies indicate that the intra-atomic spin-orbit coupling and
the orbital magnetism are indispensable for the physically adequate description
of electronic and magnetic properties of LaMnO3.
Keywords: 3d oxides, crystal field, spin-orbit coupling, LaMnO3
PACS: 71.70Ej, 75.10DgComment: 5 pages, 2 figures, in RevTex
Strain-engineered magnetic order in (LaMnO)/(SrMnO) superlattices
Using first-principles calculations based on the density functional theory,
we show a strong strain dependence of magnetic order in
(LaMnO)/(SrMnO) (001) superlattices with . The
epitaxial strain lifts the degeneracy of Mn orbitals, thus inducing an
inherent orbital order, which in turn strongly affects the ferromagnetic double
exchange of itinerant electrons, competing with the antiferromagnetic
superexchange of localized electrons. For the case of tensile strain
induced by SrTiO (001) substrate, we find that the ground state is A-type
antiferromagnetic and orbital ordered, which is in excellent
agreement with recent experiments [S. J. May {\it et al.}, Nature Materials
{\bf 8}, 892 (2009)]. Instead, for the case of compressive strain induced by
LaAlO (001) substrate, we predict that the ground state is C-type
antiferromagnetic and orbital ordered.Comment: The paper is accepted for publication in Phys. Rev.
Muon Spin Relaxation Study of (La, Ca)MnO3
We report predominantly zero field muon spin relaxation measurements in a
series of Ca-doped LaMnO_3 compounds which includes the colossal
magnetoresistive manganites. Our principal result is a systematic study of the
spin-lattice relaxation rates 1/T_1 and magnetic order parameters in the series
La_{1-x}Ca_xMnO_3, x = 0.0, 0.06, 0.18, 0.33, 0.67 and 1.0. In LaMnO_3 and
CaMnO_3 we find very narrow critical regions near the Neel temperatures T_N and
temperature independent 1/T_1 values above T_N. From the 1/T_1 in LaMnO_3 we
derive an exchange integral J = 0.83 meV which is consistent with the mean
field expression for T_N. All of the doped manganites except CaMnO_3 display
anomalously slow, spatially inhomogeneous spin-lattice relaxation below their
ordering temperatures. In the ferromagnetic (FM) insulating
La_{0.82}Ca_{0.18}MnO_3 and ferromagnetic conducting La_{0.67}Ca_{0.33}MnO_3
systems we show that there exists a bi-modal distribution of \muSR rates
\lambda_f and \lambda_s associated with relatively 'fast' and 'slow' Mn
fluctuation rates, respectively. A physical picture is hypothesized for these
FM phases in which the fast Mn rates are due to overdamped spin waves
characteristic of a disordered FM, and the slower Mn relaxation rates derive
from distinct, relatively insulating regions in the sample. Finally, likely
muon sites are identified, and evidence for muon diffusion in these materials
is discussed.Comment: 21 pages, 17 figure
Electron Accumulation and Emergent Magnetism in LaMnO3/SrTiO3 Heterostructures
Emergent phenomena at polar-nonpolar oxide interfaces have been studied
intensely in pursuit of next-generation oxide electronics and spintronics. Here
we report the disentanglement of critical thicknesses for electron
reconstruction and the emergence of ferromagnetism in polar-mismatched
LaMnO3/SrTiO3 (001) heterostructures. Using a combination of element-specific
X-ray absorption spectroscopy and dichroism, and first-principles calculations,
interfacial electron accumulation and ferromagnetism have been observed within
the polar, antiferromagnetic insulator LaMnO3. Our results show that the
critical thickness for the onset of electron accumulation is as thin as 2 unit
cells (UC), significantly thinner than the observed critical thickness for
ferromagnetism of 5 UC. The absence of ferromagnetism below 5 UC is likely
induced by electron over-accumulation. In turn, by controlling the doping of
the LaMnO3, we are able to neutralize the excessive electrons from the polar
mismatch in ultrathin LaMnO3 films and thus enable ferromagnetism in films as
thin as 3 UC, extending the limits of our ability to synthesize and tailor
emergent phenomena at interfaces and demonstrating manipulation of the
electronic and magnetic structures of materials at the shortest length scales.Comment: Accepted by Phys. Rev. Let
First Principles Study of Structural, Electronic and Magnetic Interplay in Ferroelectromagnetic Yttrium Manganite
We present results of local spin density approximation pseudopotential
calculations for the ferroelectromagnet, yttrium manganite (YMnO3). The origin
of the differences between ferroelectric and non-ferroelectric perovskite
manganites is determined by comparing the calculated properties of yttrium
manganite in its ferroelectric hexagonal and non-ferroelectric orthorhombic
phases. In addition, orthorhombic YMnO3 is compared with the prototypical
non-ferroelectric manganite, lanthanum manganite. We show that, while the
octahedral crystal field splitting of the cubic perovskite structure causes a
centro-symmetric Jahn-Teller distortion around the Mn3+ ion, the markedly
different splitting in hexagonal perovskites creates an electronic
configuration consistent with ferroelectric distortion. We explain the nature
of the distortion, and show that a local magnetic moment on the Mn3+ ion is a
requirement for it to occur.Comment: Replacement of earlier version with error in pseudopotentia
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