19 research outputs found
The spin-1/2 coupled tetramer system Ba(TiO)Cu(PO) probed by magnetization, specific heat, and P-NMR
We present the synthesis and a detailed investigation of structural and
magnetic properties of polycrystalline Ba(TiO)Cu(PO) (BTCPO)
via x-ray diffraction, magnetic susceptibility, heat capacity, and P
Nuclear Magnetic Resonance (NMR) measurements. BTCPO has a 2D layered structure
with interlinked CuO tetramer units. A broad maximum is observed
around 16.5 K in our magnetization data accompanied by a sharp anomaly around
= 9.5 K in the heat capacity. An anomaly at = 9.5 K is also found in
the temperature dependence of the P NMR spin-lattice relaxation rate
. A power law behavior for the heat capacity as well as for the P
below the ordering temperature could be obtained. The P NMR
lineshape is asymmetric and the NMR shift tracks the bulk spin-susceptibility.
We estimated the isotropic and axial components of the hyperfine coupling
tensor to be as the and
, respectively.Comment: 8 pages, 3 tables, 13 figure
Structural, thermodynamic, and local probe investigations of a honeycomb material AgLiMnO
The system Ag[LiMn]O belongs to a quaternary
3R-delafossite family and crystallizes in a monoclinic symmetry with space
group and the magnetic Mn() ions form a honeycomb
network in the -plane. An anomaly around 50 K and the presence of
antiferromagnetic (AFM) coupling (Curie-Weiss temperature
K) were inferred from our magnetic susceptibility data. The magnetic specific
heat clearly manifests the onset of magnetic ordering in the vicinity of 48\,K
and the recovered magnetic entropy, above the ordering temperature, falls short
of the expected value, implying the presence of short-range magnetic
correlations. The (ESR) line broadening on approaching the ordering temperature
could be described in terms of a Berezinski-Kosterlitz-Thouless
(BKT) scenario with K. Li NMR line-shift probed as a
function of temperature tracks the static susceptibility (K) of
magnetically coupled Mn ions. The Li spin-lattice relaxation rate
(1/) exhibits a sharp decrease below about 50 K. Combining our bulk
and local probe measurements, we establish the presence of an ordered ground
state for the honeycomb system AgLiMnO.Our ab-initio
electronic structure calculations suggest that in the -plane, the nearest
neighbor (NN) exchange interaction is strong and AFM, while the next NN and the
third NN exchange interactions are FM and AFM respectively. In the absence of
any frustration the system is expected to exhibit long-range, AFM order, in
agreement with experiment.Comment: 11 pages, 13 figures, accepted in Phys Rev
Unconventional magnetism in the 4d based () honeycomb system AgLiRuO
We have investigated the thermodynamic and local magnetic properties of the
Mott insulating system AgLiRuO containing Ru
(4) for novel magnetism. The material crystallizes in a monoclinic
structure with RuO octahedra forming an edge-shared
two-dimensional honeycomb lattice with limited stacking order along the
-direction. The large negative Curie-Weiss temperature ( = -57
K) suggests antiferromagnetic interactions among Ru ions though magnetic
susceptibility and heat capacity show no indication of magnetic long-range
order down to 1.8 K and 0.4 K, respectively. Li nuclear magnetic
resonance (NMR) shift follows the bulk susceptibility between 120-300 K and
levels off below 120 K. Together with a power-law behavior in the temperature
dependent spin-lattice relaxation rate between 0.2 and 2 K, it suggest dynamic
spin correlations with gapless excitations. Electronic structure calculations
suggest an description of the Ru-moments and the possible importance of
further neighbour interactions as also bi-quadratic and ring-exchange terms in
determining the magnetic properties. Analysis of our SR data indicates
spin freezing below 5 K but the spins remain on the borderline between static
and dynamic magnetism even at 20 mK.Comment: 10 pages, 11 figures. accepted in Phys. Rev.
Gapless quantum spin liquid in the triangular system SrCuSbO
We report gapless quantum spin liquid behavior in the layered triangular
SrCuSbO (SCSO) system. X-ray diffraction shows superlattice
reflections associated with atomic site ordering into triangular Cu planes
well-separated by Sb planes. Muon spin relaxation (SR) measurements show
that the moments at the magnetically active Cu sites remain
dynamic down to 65 mK in spite of a large antiferromagnetic exchange scale
evidenced by a large Curie-Weiss temperature
-143 K as extracted from the bulk susceptibility. Specific heat measurements
also show no sign of long-range order down to 0.35 K. The magnetic specific
heat () below 5 K reveals a
+ behavior. The
significant contribution to the magnetic specific heat invites a
phenomenology in terms of the so-called Dirac spinon excitations with a linear
dispersion. From the low- specific heat data, we estimate the dominant
exchange scale to be 36 K using a Dirac spin liquid ansatz which is not
far from the values inferred from microscopic density functional theory
calculations ( 45 K) as well as high-temperature susceptibility analysis
( 70 K). The linear specific heat coefficient is about 18 mJ/mol-K
which is somewhat larger than for typical Fermi liquids.Comment: 16 pages, 21 figures, including supplementary material. A Dirac spin liquid scenario has been put forward to explain the
field-dependent specific heat data. Comments are welcom
Infield X-ray diffraction studies of field and temperature driven structural phase transition in Nd0.49Sr0.51MnO3+delta
Comprehensive X-ray diffraction (XRD) studies have been performed at different temperature (T) (4.2-300 K) and magnetic field (H) (0-8 T) to understand the evolution of crystal structure of Nd0.49Sr0.51MnO3+delta (NSMO) under non ambient conditions. The T dependent XRD results show the abrupt change in the lattice parameters without any change in lattice symmetry at similar to 200 K, which is associated with the first order structural phase transition from ferromagnetic to antiferromagnetic phase. This phase transition is strongly H dependent and shifted to lower temperature (similar to 150 K) on the application of 8 T field with phase coexistence (high temperature phase similar to 18%), even down to 4.2 K. Isothermal XRD results at 150 K under different H clearly illustrate the H induced first order structural phase transition. The critical H at which this phase transformation starts is similar to 1 T, with rapid growth above 4 T with hysteretic nature during increasing and decreasing H. These results are supported with the resistivity and magnetoresistance results and affirm the strong spin-lattice coupling in NSMO. Our detail studies reveal the structural correlations to the observed colossal magnetoresistance and magnetocaloric effect in this material. (C) 2017 Elsevier B.V. All rights reserved
Spin-1/2 chain compound Ba<sub>2</sub>Cu<sub>2</sub>Te<sub>2</sub>P<sub>2</sub>O<sub>13</sub>: Magnetization, specific heat, and local-probe NMR
Studies on magnetic field and temperature driven magneto-structural phase transition in La0.5Sr0.5MnO3+delta
The influence of magnetic field on the crystal structure of colossal magnetoresistance (CMR) material La0.5Sr0.5MnO3+delta has been investigated. Low temperature high-magnetic field powder X-ray diffraction (XRD) measurements were carried out on La0.5Sr0.5MnO3+delta in temperature range from 4.2 to 300 K and magnetic field range from 0 to 8 T. A first order structural phase transition from tetragonal I4/mcm to orthorhombic Fmmm phase, coupled with reported electronic and magnetic phase transition from ferromagnetic metal to antiferromagnetic insulator state has been started at similar to 200 K and completed at similar to 100 K. On the application of 8 T magnetic field this magneto-structural phase transition shifted to lower temperature (similar to 162 K) with phase coexistence regime down to 4.2 K. Isothermal X-ray diffraction measurements at 150 K infer the evidence of magnetic field driven first order structural phase transition from Fmmm to I4/mcm. These results consistent with the resistivity and magnetoresistance results; present the microscopic evidence of strong spin-lattice coupling and reveal the magnetic field driven structural phase transition as the origin of observed colossal magnetoresistance in this material. (C) 2016 Published by Elsevier B.V
Charge ordering in B-site Mo doped Pr0.20Sr0.80Mn1-xMoxO3-delta
The temperature dependent structural, transport and magnetic properties of Pr0.20Sr0.80Mn1-xMoxO3-delta (x - 0.0, 0.02, 0.04 and 0.10) have been studied using low-temperature x-ray and electron diffraction, resistivity and dc magnetization measurements. Unlike the undoped (x = 0) sample, which is cubic at room temperature, the Mo doped samples show phase coexistence of cubic (Pm3m) and tetragonal (I4/ mcm; c/root 2 > a) phases. The Mo doping stabilizes the tetragonal (I4/mcm) phase in the temperature range of 300-330 K. The tetragonality of the sample for x = 0.10 however appears to be of different kind, which further under goes an additional transition from tetragonal to orthorhombic (Fmmm) phase below 200 K. Transmission electron microscopy, employing electron-diffraction and high-resolution microstructural imaging, clearly reveals the occurrence of charge-ordering (CO) for x = 0.04 and 0.10 samples with non-integral modulation along [110] type perovskite direction. The dc magnetization and resistivity data very well correlate with the observed structural and associated CO antiferromagnetic phase transitions. The increased stability of the distorted perovskite phases and the occurrence of CO are found to correlate with the increase in the Mn3+/ Mn4+ ratio as a function of Mo6+ substitution. The possible role of effective B-site cation size in stabilizing the distorted perovskite phase has been discussed in terms of tolerance factor. (C) 2017 Elsevier B.V. All rights reserved