21 research outputs found
Metamagnetic and electronic transitions in charge-ordered Nd0.50Ca0.47Ba0.03MnO3 manganite
The ABO3 type charge-ordered antiferromagnetic Nd0.50Ca0.50MnO3 (NCMO)
manganite is doped at A-site by 3 % of Ba2+ for Ca2+. The resulting system,
Nd0.50Ca0.47Ba0.03MnO3 (NCBMO), is studied for the effects of Ba doping on the
magnetic and electronic properties. On application of magnetic field to NCBMO,
strongly correlated successive sharp metamagnetic and electronic transitions
are observed from antiferromagnetic-insulating to ferromagnetic-metallic state
at 2.5 K. The critical magnetic field (Hc) required for metamagnetism is found
to reduce drastically from 15 T for undoped NCMO to 3 T for NCBMO. On
increasing the temperature, the Hc of NCBMO passes through a minimum. This
behavior of Hc of NCBMO contrasts to that of NCMO. The results are discussed in
context of A-site cation disorder and size
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
The flux pinning force and vortex phase diagram of single crystal FeTe0.60Se0.40
The flux pinning force density (Fp) of the single crystalline FeTe0.60Se0.40
superconductor has been calculated from the magnetization measurements. The
normalized Fp versus h (=H/Hirr) curves are scaled using the Dew-Hughes formula
to underline the pinning mechanism in the compound. The obtained values of
pinning parameters p and q indicate the vortex pinning by the mixing of the
surface and the point core pinning of the normal centers. The vortex phase
diagram has also been drawn for the first time for the FeTe0.60Se0.40, which
has very high values of critical current density Jc ~ 1.10(5) Amp/cm2 and the
upper critical field Hc2(0) = 65T, with a reasonably high transition
temperature Tc =14.5K.Comment: 12 pages, 4 figure
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
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 anomalies in the spin chain system, SrCuZnIrO
We report the results of ac and dc magnetization (M) and heat-capacity (C)
measurements on the solid solution, SrCuZnIrO. While the Zn
end member is known to form in a rhombohedral pseudo one-dimensional
KCdCl structure with an antiferromagnetic ordering temperature of
(T =) 19 K, the Cu end member has been reported to form in a monoclinically
distorted form with a Curie temperature of (T =) 19 K. The magnetism of the
Zn compound is found to be robust to synthetic conditions and is broadly
consistent with the behavior known in the literature. However, we find a lower
magnetic ordering temperature (T) for our Cu compound (~ 13 K), thereby
suggesting that T is sensitive to synthetic conditions. The Cu sample
appears to be in a spin-glass-like state at low temperatures, judged by a
frequency dependence of ac magnetic susceptibility and a broadening of the C
anomaly at the onset of magnetic ordering, in sharp contrast to earlier
proposals. Small applications of magnetic field, however, drive this system to
ferromagnetism as inferred from the M data. Small substitutions for Cu/Zn (x =
0.75 or 0.25) significantly depress magnetic ordering; in other words, T
varies non-monotonically with x (T ~ 6, 3 and 4 K for x = 0.25, 0.5, and
0.67 respectively). The plot of inverse susceptibility versus temperature is
non-linear in the paramagnetic state as if correlations within (or among) the
magnetic chains continuously vary with temperature. The results establishComment: 7 pages, 7 figures, Revte
Magnetic anomalies in single crystalline Tb5Si3
The polycrystalline form of the compound, Tb5Si3, crystallizing in
Mn5Si3-type hexagonal structure, which was earlier believe to order
antiferromagnetically below 69 K, has been recently reported by us to exhibit
interesting magnetoresistance (MR) anomalies. In order to understand the
magnetic anomalies of this compound better, we synthesized single crystals of
this compound and subjected them to intense magnetization and MR studies. The
results reveal that the magnetic behavior is strongly anisotropic as the easy
axis is along a basal plane. There appear to be multiple magnetic features in
the close vicinity of 70 K. In addition, there are multiple steps in isothermal
magnetization (which could not be resolved in the data for polycrystalline
data) for magnetic-field (H) along a basal plane. The sign of MR is positive in
the magnetically ordered state, and, interestingly, the magnitude dramatically
increases at the initial step for H parallel to basal plane, but decreases at
subsequent steps as though the origin of these steps are different. However,
for the perpendicular orientation (H || [0 0 0 1]), there is no evidence for
any step either in M(H) or in MR(H). These results establish this compound is
an interesting magnetic material