37 research outputs found
Uniaxial magnetocrystalline anisotropy in
is a paramagnetic metal and since its low temperature
resistivity is described by with , it
is also considered a non-Fermi liquid (NFL) metal. We have performed extensive
magnetoresistance and Hall effect measurements of untwinned epitaxial films of
. These measurements reveal that exhibits
uniaxial magnetocrystalline anisotropy. In addition, the low-temperature NFL
behavior is most effectively suppressed when a magnetic field is applied along
the easy axis, suggesting that critical spin fluctuations, possibly due to
proximity of a quantum critical phase transition, are related to the NFL
behavior.Comment: 7 figure
Structural, electronic and magnetic properties of SrRuO under epitaxial strain
Using density functional theory within the local spin density approximation,
structural, electronic and magnetic properties of SRO are investigated. We
examine the magnitude of the orthorhombic distortion in the ground state and
also the effects of applying epitaxial constraints, whereby the influence of
large (in the range of ) in-plane strain resulting from coherent
epitaxy, for both [001] and [110] oriented films, have been isolated and
investigated. The overall pattern of the structural relaxations reveal coherent
distortions of the oxygen octahedra network, which determine stability of the
magnetic moment on the Ru ion. The structural and magnetic parameters exhibit
substantial changes allowing us to discuss the role of symmetry and
possibilities of magneto-structural tuning of \SRO-based thin film structures.Comment: 11 page
Transport Properties, Thermodynamic Properties, and Electronic Structure of SrRuO3
SrRuO is a metallic ferromagnet. Its electrical resistivity is reported
for temperatures up to 1000K; its Hall coefficient for temperatures up to 300K;
its specific heat for temperatures up to 230K. The energy bands have been
calculated by self-consistent spin-density functional theory, which finds a
ferromagnetic ordered moment of 1.45 per Ru atom. The measured
linear specific heat coefficient is 30mJ/mole, which exceeds the
theoretical value by a factor of 3.7. A transport mean free path at room
temperature of is found. The resistivity increases nearly
linearly with temperature to 1000K in spite of such a short mean free path that
resistivity saturation would be expected. The Hall coefficient is small and
positive above the Curie temperature, and exhibits both a low-field and a
high-field anomalous behavior below the Curie temperature.Comment: 6 pages (latex) and 6 figures (postscript, uuencoded.) This paper
will appear in Phys. Rev. B, Feb. 15, 199
Investigation of the ferromagnetic transition in the correlated 4d perovskites SrRuRhO
The solid-solution SrRuRhO () is a
variable-electron-configuration system forming in the nearly-cubic-perovskite
basis, ranging from the ferromagnetic 4 to the enhanced paramagnetic
4. Polycrystalline single-phase samples were obtained over the whole
composition range by a high-pressure-heating technique, followed by
measurements of magnetic susceptibility, magnetization, specific heat,
thermopower, and electrical resistivity. The ferromagnetic order in long range
is gradually suppressed by the Rh substitution and vanishes at .
The electronic term of specific-heat shows unusual behavior near the critical
Rh concentration; the feature does not match even qualitatively with what was
reported for the related perovskites (Sr,Ca)RuO. Furthermore, another
anomaly in the specific heat was observed at .Comment: Accepted for publication in PR
Antiferromagnetic Order in Disorder-Induced Insulating Phase of SrRu_{1-x}Mn_xO_3 (0.4<x<0.6)
We have performed the powder neutron diffraction measurements on the solid
solutions of SrRu_{1-x}Mn_xO_3, and found that the itinerant ferromagnetic
order observed in pure SrRuO_3 changes into the C-type antiferromagnetic (AF)
order with nearly localized d electrons in the intermediate Mn concentration
between x=0.4 and 0.6. With increasing x, the AF moment is strongly enhanced
from 1.1 mB (x=0.4) to 2.6 mB (x=0.6), which is accompanied by the elongation
of the tetragonal c/a ratio. These results suggest that the substitution of Mn
for Ru suppresses the itinerant character of the d electrons, and induces the
superexchange interaction through the compression in the c plane. We have also
found that the magnetic and transport properties observed in our tetragonal
samples are quite similar to those of recently reported orthorhombic ones.Comment: 4 pages, 4 figure
Electronic properties of bulk and thin film SrRuO: a search for the metal-insulator transition
We calculate the properties of the 4 ferromagnet SrRuO in bulk and
thin film form with the aim of understanding the experimentally observed metal
to insulator transition at reduced thickness. Although the spatial extent of
the 4 orbitals is quite large, many experimental results have suggested that
electron-electron correlations play an important role in determining this
material's electronic structure. In order to investigate the importance of
correlation, we use two approaches which go beyond the conventional local
density approximation to density functional theory (DFT): the local spin
density approximation + Hubbard (LSDA+) and the pseudopotential
self-interaction correction (pseudo-SIC) methods. We find that the details of
the electronic structure predicted with the LSDA do not agree with the
experimental spectroscopic data for bulk and thin film SrRuO. Improvement
is found by including electron-electron correlations, and we suggest that bulk
orthorhombic SrRuO is a {\it weakly strongly-correlated} ferromagnet whose
electronic structure is best described by a 0.6 eV on-site Hubbard term, or
equivalently with corrections for the self-interaction error. We also perform
{\it ab initio} transport calculations that confirm that SrRuO has a
negative spin polarization at the Fermi level, due to the position of the
minority Ru 4 band center. Even with correlations included in our
calculations we are unable to reproduce the experimentally observed
metal-insulator transition, suggesting that the electronic behavior of
SrRuO ultra-thin films might be dominated by extrinsic factors such as
surface disorder and defects.Comment: 15 pages, 12 figures, 3 table
Novel critical exponent of magnetization curves near the ferromagnetic quantum phase transitions of Sr1-xAxRuO3 (A = Ca, La0.5Na0.5, and La)
We report a novel critical exponent delta=3/2 of magnetization curves
M=H^{1/delta} near the ferromagnetic quantum phase transitions of Sr1-xAxRuO3
(A = Ca, La0.5Na0.5, and La), which the mean field theory of the
Ginzburg-Landau-Wilson type fails to reproduce. The effect of dirty
ferromagnetic spin fluctuations might be a key.Comment: 4 pages, 5 figure
The ground state of Sr3Ru2O7 revisited; Fermi liquid close to a ferromagnetic instability
We show that single-crystalline Sr3Ru2O7 grown by a floating-zone technique
is an isotropic paramagnet and a quasi-two dimensional metal as spin-triplet
superconducting Sr2RuO4 is. The ground state is Fermi liquid with very low
residual resistivity (3 micro ohm cm for in-plane currents) and a nearly
ferromagnetic metal with the largest Wilson ratio Rw>10 among paramagnets so
far. This contrasts with the ferromagnetic order at Tc=104 K reported on single
crystals grown by a flux method [Cao et al., Phys. Rev. B 55, R672 (1997)]. We
have also found a dramatic changeover from paramagnetism to ferromagnetism
under applied pressure. This suggests the existence of a substantial
ferromagnetic instability on the verge of a quantum phase transition in the
Fermi liquid state.Comment: 5 pages, 4 figures, to be published in Phys. Rev. B : Rapid co
Nuclear Magnetic Resonance and Magnetization Studies of the Ferromagnetic Ordering Temperature Suppression in Ru Deficient SrRuO3
The synthesis of SrRuO3 under high-pressure oxygen produces a
nonstoichiometric form with randomly distributed vacancies on the Ru-sites,
along with a significantly reduced ferromagnetic ordering temperature. In order
to gain additional insight into the suppression of the ferromagnetism, local
studies utilizing 99,101 Ru zero-field spin-echo NMR, and Ru K-edge XAFS, along
with complimentary magnetization and x-ray diffraction measurements, have been
carried out on samples of SrRuO3 annealed at both ("ambient") atmospheric
pressure and "high-pressure" oxygen (600 atm). Consistent with previous work,
the NMR spectrum for "ambient" SrRuO3 consists of two well-defined peaks at
64.4 MHz and 72.2 MHz corresponding to the 99Ru and 101Ru isotopes,
respectively, and a hyperfine field of 329 kG. Although the magnetization
measurements show a lower ferromagnetic ordering temperature for the
"high-pressure" oxygen sample (90 K compared to 160 K for the "ambient"
sample), the NMR spectrum shows no significant shift in the two peak
frequencies. However, the two peaks exhibit considerable broadening, along with
structure on both the low and high frequency sides which is believed to be
quadrupolar in origin. Analysis of the Ru K-edge XAFS reveals more disorder in
the Ru-O bond for the "high-pressure" oxygen sample compared to the "ambient"
sample. Furthermore, XANES of Ru K-edge analysis indicates no difference in the
valence of Ru between the two samples. The magnetic behavior indicates the
existence of some vacancies on the Ru sites for the "high-pressure" oxygen
sample.Comment: Proceedings of the 3rd Polish-US Workshop on Magnetism and
Superconductivity of Advanced Materials, July 14-19, 2002, Ladek Zdroj
(Poland), to appear in Physica
Violation of the Mott-Ioffe-Regel Limit: High-temperature Resistivity of Itinerant Magnets Srn+1RunO3n+1 (n=2,3,infinity) and CaRuO3
Srn+1RunO3n+1 represents a class of layered materials whose physical
properties are a strong function of the number of Ru-O layers per unit cell, n.
This series includes the p-wave superconductor Sr2RuO4 (n=1), enhanced
paramagnetic Sr3Ru2O7 (n=2), nearly ferromagnetic Sr4Ru3O10 (n=3) and itinerant
ferromagnetic SrRuO3 (n=infinity). In spite of a wide spectrum of physical
phenomena, this series of materials along with paramagnetic CaRuO3 shares two
major characteristics, namely, robust Fermi liquid behavior at low temperatures
and anomalous transport behavior featured by linear temperature dependence of
resistivity at high temperature where electron wavepackets are no longer
clearly defined. There is no crossover separating such two fundamentally
different states. In this paper, we report results of our study that
systematically addresses anisotropy and temperature dependence of basal-plane
and c-axis resistivity as a function of n for the entire Srn+1RunO3n+1 series
and CaRuO3 and for a wide temperature range of 1.7 K<T<900 K. It is found that
the anomalous transport behavior correlates with magnetic susceptibility and
becomes stronger with decreasing dimensionality. Implications of these results
are discussed