45 research outputs found
Superparamagnetic-like ac susceptibility behavior in a "partially disordered antiferromagnetic" compound, CaCoRhO
We report the results of dc and ac magnetization measurements as a function
of temperature (1.8 - 300 K) for the spin chain compound, CaCoRhO,
which has been recently reported to exhibit a partially disordered
antiferromagnetic (PDAF) structure in the range 30 - 90 K and spin-glass
freezing below 30 K. We observe an unexpectedly large frequency dependence of
ac susceptibility in the T range 30 - 90 K, typical of superparamagnets. In
addition, we find that there is no difference in the isothermal remanent
magnetization behavior for the two regimes below 90 K. These findings call for
more investigations to understand the magnetism of this compound.Comment: 4 pages, 3 figure
Phonon, Two-Magnon and Electronic Raman Scattering of Fe1+yTe1-xSex
We have measured Raman scattering spectra of single-crystalline FeTe0.6Se0.4
(T_c ~ 14.5 K) and its parent compound Fe1.074Te at various temperatures. In
the parent compound Fe1.074Te, A1g and B1g modes have been observed at 157.5
and 202.3 cm-1, respectively, at 5 K. These frequencies qualitatively agree
with the calculated results. Two-magnon excitation has been observed around
2300 cm-1 for both compounds. Temperature dependence between the electronic
Raman spectra below and above T_c has been observed and 2\Delta and
2\Delta/k_BT_C have been estimated as 5.0 meV and 4.0, respectively.Comment: 8 pages, 8 figures, to be published in Phys. Rev.
Magnetic anisotropy and geometrical frustration in the Ising spin-chain system Sr5Rh4O12
A structural and thermodynamic study of the newly synthesized single crystal
Sr5Rh4O12 is reported. Sr5Rh4O12 consists of a triangular lattice of spin
chains running along the c-axis. It is antiferromagnetically ordered below 23 K
with the intrachain and interchain coupling being ferromagnetic (FM) and
antiferromagnetic (AFM), respectively. There is strong evidence for an Ising
character in the interaction and geometrical frustration that causes incomplete
long-range AFM order. The isothermal magnetization exhibits two step-like
transitions leading to a ferrimagnetic state at 2.4 T and a FM state at 4.8 T,
respectively. Sr5Rh4O12 is a unique frustrated spin-chain system ever found in
4d and 5d based materials without a presence of an incomplete 3d-electron
shell.Comment: 15 pages, 4 figure
Electron Correlation Driven Heavy-Fermion Formation in LiV2O4
Optical reflectivity measurements were performed on a single crystal of the
d-electron heavy-fermion (HF) metal LiV2O4. The results evidence the highly
incoherent character of the charge dynamics for all temperatures above T^*
\approx 20 K. The spectral weight of the optical conductivity is redistributed
over extremely broad energy scales (~ 5 eV) as the quantum coherence of the
charge carriers is recovered. This wide redistribution is, in sharp contrast to
f-electron Kondo lattice HF systems, characteristic of a metallic system close
to a correlation driven insulating state. Our results thus reveal that strong
electronic correlation effects dominate the low-energy charge dynamics and
heavy quasiparticle formation in LiV2O4. We propose the geometrical
frustration, which limits the extension of charge and spin ordering, as an
additional key ingredient of the low-temperature heavy-fermion formation in
this system.Comment: 5 pages, 3 figure
Magnetic behavior of spin-chain compounds, Sr3ZnRhO6 and Ca3NiMnO6, from heat capacity and ac susceptibility studies
Heat-capacity (C) and ac susceptibility measurements have been performed on
the spin-chain compounds, Sr3ZnRhO6 and Ca3NiMnO6, to establish their magnetic
behavior and to explore whether there are magnetic frustration effects due to
antiferromagnetic coupling of the chains arranged in a triangular fashion.
While the paramagnetic Curie temperatures have been known to be large with a
negative sign, as though antiferromagnetic interaction is very strong, the
results establish that (i) the former apparently undergoes inhomogeneous
magnetic ordering only around 15 K, however without spin-glass anomalies, and
(ii) the latter orders antiferromagnetically at a relatively low temperature
(17 K). Thus, the magnetic frustration manifests differently in these
compounds.Comment: J. Solid State Chemistry, in pres
Partial Disorder and Metal-Insulator Transition in the Periodic Anderson Model on a Triangular Lattice
Ground state of the periodic Anderson model on a triangular lattice is
systematically investigated by the mean-field approximation. We found that the
model exhibits two different types of partially disordered states: one is at
half filling and the other is at other commensurate fillings. In the latter
case, the kinetic energy is lowered by forming an extensive network involving
both magnetic and nonmagnetic sites, in sharp contrast to the former case in
which the nonmagnetic sites are rather isolated. This spatially extended nature
of nonmagnetic sites yields a metallic partially-disordered state by hole
doping. We discuss the mechanism of the metal-insulator transition by the
change of electronic structure.Comment: 4 pages, 4 figures, accepted for publication in J. Phys. Soc. Jp
Specific heat and magnetization study on single crystals of a frustrated, quasi one-dimensional oxide: Ca3Co2O6
Specific heat and magnetization measurements have been carried out under a
range of magnetic fields on single crystals of Ca3Co2O6. This compound is
composed of Ising magnetic chains that are arranged on a triangular lattice.
The intrachain and interchain couplings are ferromagnetic and
antiferromagnetic, respectively. This situation gives rise to geometrical
frustration, that bears some similarity to the classical problem of a
two-dimensional Ising triangular antiferromagnet. This paper reports on the
ordering process at low-T and the possibility of one-dimensional features at
high-T.Comment: 7 pages, 6 figures, accepted for publication in PR
Long range magnetic ordering in a spin-chain compound, CaCuMnO, with multiple bond distances
The results of ac and dc magnetization and heat capacity measurements as a
function of temperature (T = 1.8 to 300 K) are reported for a
quasi-one-dimensional compound, CaCuMnO, crystallizing in a
triclinically distorted KCdCl-type structure. The results reveal that
this compound undergoes antiferromagnetic ordering close to 5.5 K. In addition,
there is another magnetic transition below 3.6 K. Existence of two long-range
magnetic transitions is uncommon among quasi-one-dimensional systems. It is
interesting to note that both the magnetic transitions are of long-range type,
instead of spin-glass type, in spite of the fact that the Cu-O and Mn-O bond
distances are multiplied due to this crystallographic distortion. In view of
this, this compound could serve as a nice example for studying
"order-in-disorder" phenomena.Comment: Physical Review (in press
Magnetic frustration in a stoichiometric spin-chain compound, CaCoIrO
The temperature dependent ac and dc magnetization and heat capacity data of
CaCoIrO, a spin-chain compound crystallizing in a KCdCl-derived
rhombohedral structure, show the features due to magnetic ordering of a
frustrated-type below about 30 K, however without exhibiting the signatures of
the so-called "partially disordered antiferromagnetic structure" encountered in
the isostructural compounds, CaCoO and CaCoRhO. This class
of compounds thus provides a variety for probing the consequences of magnetic
frustration due to topological reasons in stoichiometric spin-chain materials,
presumably arising from subtle differences in the interchain and intrachain
magnetic coupling strengths. This compound presents additional interesting
situations in the sense that, ac susceptibility exhibits a large frequency
dependence in the vicinity of 30 K uncharacteristic of conventional
spin-glasses, with this frustrated magnetic state being robust to the
application of external magnetic fields.Comment: Physical Review (Rapid Communications), in pres