46 research outputs found
Magnetic and electrical resistance behaviour of the oxides, CaYLiRuO (x= 0.0, 0.5 and 1.0)
We have investigated the magnetic and electrical resistance behaviour of
CaYLiRuO. The parent compound exhibits magnetic ordering from
Ru sublattice at a rather high temperature, 113 K. Though the paramagnetic
Curie temperature () is negative indicative of antiferromagnetic
ordering, the large magnitude (-250 K) of reveals complex nature
of the magnetism in this compound. Ru ions appear to be in the pentavalent
state. We note that the N\'eel temperature undergoes only a marginal reduction
by Y substitution. All these compositions are found to be insulators and thus
the electron doping does not result in metallicity. Thus the overall magnetic
and transport behaviour are found to be essentially insensitive to Y
substitution for Ca, a finding which may favour the idea of
quasi-one-dimensional magnetism in these compounds.Comment: 5 pages of text in RevTex, 6 figures, Solid State Communications (in
press
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
Effect of a small disruption of the Ca site on the geometrically frustrated magnetic behavior of Ca3CoRhO6
The compound, Ca3CoRhO6, containing magnetic Co-Rh chains intervened by Ca
ions, has been known to be one of the few exhibiting partially disordered
antiferromagnetic structure (PDA) due to geometrical frustration. Here, we
report the influence of partial replacement of Ca by Y on the magnetic
anomalies by investigating the solid solution, Ca(3-x)Y(x)CoRhO6 by bulk
measurements. There are profound changes in the magnetic behavior, the most
notable one being that the features attributable to spin-chain magnetism and
PDA structure get suppressed dramatically by a small replacement of Ca by Y (x=
0.15), despite the fact that the magnetic chain is not disrupted. This finding
suggests that this compound is on the verge of PDA-structural-instability.Comment: 10 pages including 5 figure
Electrical resistivity and tunneling anomalies in CeCuAs2
The compound CeCuAs2 is found to exhibit negative temperature (T) coefficient
of electrical resistivity (rho) under ambient pressure conditions in the entire
T-range of investigation (45 mK to 300 K), even in the presence of high
magnetic fields. Preliminary tunneling spectroscopic measurements indicate the
existence of a psuedo-gap at least at low temperatures, thereby implying that
this compound could be classified as a Kondo semi-conductor, though rho(T)
interestingly is not found to be of an activated type.Comment: To appear in the proceedings of SCES200
Contrasting magnetic behavior of fine particles of some Kondo Lattices
We have investigated the magnetic behavior of ball-milled fine particles of
well-known Kondo lattices, CeAu2Si2, CePd2Si2 and CeAl2, by magnetization and
heat-capacity studies in order to understand the magnetic behavior when the
particle size is reduced. These compounds have been known to order
antiferromagnetically in the bulk form near (TN=) 10, 10 and 3.8 K
respectively. We find that the features due to magnetic ordering get suppressed
to temperatures below 1.8 K in the case of fine particles of ternary alloys,
though trivalence of Ce as inferred from the effective moment remains
unchanged. In contrast to this, in CeAl2, there appears to be a marginal
enhancement of TN, when the particle size is reduced to less than a micron.
These results can be consistently understood by proposing that there is
relatively more 4f-localization as the particle size is reduced, resulting in
weakening of exchange interaction strength
Superconducting behavior of the solid solution, Y2Pd(1-x)Pt(x)Ge3
The compound Y2PdGe3 was earlier reported by us to be one of the very few
ternary superconducting compounds (T_c= 3 K) belonging to the same structure as
that of MgB2. Here we report the results of electrical resistivity,
magnetization and heat capacity measurements at low temperatures on the solid
solution with a nominal starting composition, Y2Pd(1-x)Pt(x)Ge3, to understand
the influence of gradual replacement of Pd by Pt on T_c. The superconducting
properties of this solution is distinctly interesting in the sense that the Tc
varies monotonically with increasing x in sharp contrast to the non-monotonic
variation for other isostructural solid solutions reported recently.Comment: Physica C, in pres
Magnetoresistance in ordered and disordered double perovskite oxide, SrFeMoO
We have prepared crystallographically ordered and disorder specimens of the
double perovskite, SrFeMoO and investigated their magnetoresistance
behaviour. The extent of ordering between the Fe and Mo sites in the two
samples is determined by Rietveld analysis of powder x-ray diffraction patterns
and reconfirmed by M\"{o}ssbauer studies. While the ordered sample exhibits the
sharp low-field response, followed by moderate changes in the magnetoresistance
at higher fields, the disordered sample is characterised by the absence of the
spectacular low-field response. We argue that the low field response depends
crucially on the half-metallic ferromagnetism, while the high-field response
follows from the overall magnetic nature of the sample, even in absence of the
half-metallic state.Comment: accepted in Solid State Communicatio
Large Low Temperature Magnetoresistance and Magnetic Anomalies in TbPdSi and DyPdSi
The results of heat-capacity, magnetic susceptibility, electrical resistivity
and magnetoresistance measurements on the compounds
TbPdSi and DyPdSi, are reported. The results establish that
these compounds undergo long-range magnetic ordering (presumably with a complex
magnetic structure) below (Tc=) 23 and 8 K respectively. The is negative in the vicinity of Tc and the magnitude grows as Tc is approached
from higher temperature as in the case of well-known giant magnetoresistance
systems (La manganite based perovskites); this is attributed to the formation
of some kind of magnetic polarons. The magnitude of magnetoresistance at low
temperatures is quite large, for instance, about 30% in the presence of 60 kOe
field at 5 K in the Dy sample.Comment: 4 pages, 3 figures, RevTe
Magnetic and transport anomalies in the compounds, RCuAs2 (R= Pr, Nd, Sm, Gd, Tb, Dy, Ho, and Er)
The results of dc magnetization, heat capacity, electrical resistivity (rho)
and magnetoresistance measurements are reported in detail for the compounds,
RCuAs2 for R= Pr, Nd, Sm, Gd, Tb, Dy, Ho, and Er, crystallizing in HfCuSi2-type
tetragonal structure, with the aim of bringing out anomalies among 'normal'
(that is, other than Ce and Yb) rare-earths. The results establish that all
these compounds order antiferromagnetically at low temperatures with deviations
from de Gennes scaling. Isothermal magnetization (M) data below respective Neel
temperatures (TN) reveal the existence of field-induced metamagnetic-like
transitions for most of the compounds (except R= Sm and Gd), whereas in Sm and
Gd compounds M varies essentially linearly with magnetic field. With respect to
the rho behavior, there appears to be a subtle difference in the temperature
dependence beyond 50 K between Sm on the one hand and the rest on the other. In
addition, the unexpected rho(T) minimum reported recently for R = Sm, Gd, Tb
and Dy in the paramagnetic state (around 20 to 30 K) is essentially absent for
R = Ho and Er. The results overall reveal that the normal rare-earths in this
series present an interesting situation in magnetism, warranting a new
theoretical approach to describe the transport behavior in the paramagnetic
state particularly in the vicinity of TN.Comment: Accepted for publication in Physica B (Elsevier
Heat-capacity anomalies in the presence of high magnetic fields in the spin-chain compound, Ca3Co2O6
Heat-capacity behavior in the presence of externally applied magnetic field
(H) up to 140 kOe is investigated (2-35 K) for the quasi-1-dimensional
compound, Ca3Co2O6, believed to order magnetically with the so-called partially
disordered anti-ferromagnetic structure. The results reveal that there is a
shift of the magnetic transition occurring around 24 K to a marginally higher
temperature (by 0.5 K) as H is increased from 10 to 30 kOe, uncharacteristic of
anti-ferromagnets. No peak attributable to magnetic ordering could be observed
in the entire field range of investigation in the vicinity of the second
magnetic transition, occurring around 10 K. However, hysteresis studies of
H-dependence of C indicate a subtle change in the magnetic structure as the T
is lowered across 10 K.Comment: J. Magn. Magn. Mater. (Letters