62 research outputs found
A S=1/2 vanadium-based geometrically frustrated spinel system Li2ZnV3O8
We report the synthesis and characterization of Li2ZnV3O8, which is a new
Zn-doped LiV2O4 system containing only tetravalent vanadium. A Curie-Weiss
susceptibility with a Curie-Weiss temperature of CW ~214 K suggests the
presence of strong antiferromagnetic correlations in this system. We have
observed a splitting between the zero-field cooled ZFC and field cooled FC
susceptibility curves below 6 K. A peak is present in the ZFC curve around 3.5
K suggestive of spin-freezing . Similarly, a broad hump is also seen in the
inferred magnetic heat capacity around 9 K. The consequent entropy change is
only about 8% of the value expected for an ordered S = 1=2 system. This
reduction indicates continued presence of large disorder in the system in spite
of the large CW, which might result from strong geometric frustration in
the system. We did not find any temperature T dependence in our 7Li nuclear
magnetic resonance NMR shift down to 6 K (an abrupt change in the shift takes
place below 6 K) though considerable T-dependence has been found in literature
for LiV2O4- undoped or with other Zn/Ti contents. Consistent with the above
observation, the 7Li nuclear spin-lattice relaxation rate 1/T1 is relatively
small and nearly T-independent except a small increase close to the freezing
temperature, once again, small compared to undoped or 10% Zn or 20% Ti-doped
LiV2O4.Comment: 7 pages, 8 figures, accepted in JPCM (Journal of Physics condensed
matter
Spin liquid behaviour in Jeff=1/2 triangular lattice Ba3IrTi2O9
Ba3IrTi2O9 crystallizes in a hexagonal structure consisting of a layered
triangular arrangement of Ir4+ (Jeff=1/2). Magnetic susceptibility and heat
capacity data show no magnetic ordering down to 0.35K inspite of a strong
magnetic coupling as evidenced by a large Curie-Weiss temperature=-130K. The
magnetic heat capacity follows a power law at low temperature. Our measurements
suggest that Ba3IrTi2O9 is a 5d, Ir-based (Jeff=1/2), quantum spin liquid on a
2D triangular lattice.Comment: 10 pages including supplemental material, to be published in Phys.
Rev. B (Rapid Comm.
Bose-Einstein condensation of triplons in the S=1 tetramer antiferromagnet K2Ni2(MoO4)3: A compound close to quantum critical point
The structure of K2Ni2(MoO4)3 consists of S=1 tetramers formed by Ni^{2+}
ions. The magnetic susceptibility chi(T) and specific heat Cp(T) data on a
single crystal show a broad maximum due to the low-dimensionality of the system
with short-range spin correlations. A sharp peak is seen in chi(T) and Cp(T) at
about 1.13 K, well below the broad maximum. This is an indication of magnetic
long-range order i.e., the absence of spin-gap in the ground state.
Interestingly, the application of a small magnetic field (H>0.1 T) induces
magnetic behavior akin to Bose-Einstein condensation (BEC) of triplon
excitations observed in some spin-gap materials. Our results demonstrate that
the temperature-field (T-H) phase boundary follows a power-law
(T-T_{N})propotional to H^(1/alpha) with the exponent 1/alpha close to 2/3, as
predicted for BEC scenario. The observation of BEC of triplon excitations in
small H infers that K2Ni2(MoO4)3 is located in the proximity of a quantum
critical point, which separates the magnetically ordered and spin-gap regions
of the phase diagram.Comment: 5 pages, 5 figures, Accepted in Phys. Rev. B Rapid Communication
Possible spin-orbit driven spin-liquid ground state in the double perovskite phase of Ba3YIr2O9
We report the structural transformation of hexagonal Ba3YIr2O9 to a cubic
double perovskite form (stable in ambient conditions) under an applied pressure
of 8GPa at 1273K. While the ambient pressure (AP) synthesized sample undergoes
long-range magnetic ordering at 4K, the high pressure(HP) synthesized sample
does not order down to 2K as evidenced from our susceptibility, heat capacity
and nuclear magnetic resonance (NMR) measurements. Further, for the HP sample,
our heat capacity data have the form gamma*T+beta*T3 in the temperature (T)
range of 2-10K with the Sommerfeld coefficient gamma=10mJ/mol-Ir K2. The 89Y
NMR shift has no T-dependence in the range of 4-120K and its spin-lattice
relaxation rate varies linearly with T in the range of 8-45K (above which it is
T-independent). Resistance measurements of both the samples confirm that they
are semiconducting. Our data provide evidence for the formation of a 5d based,
gapless, quantum spin-liquid (QSL) in the cubic (HP) phase of Ba3YIr2O9. In
this picture, the T term in the heat capacity and the linear variation of 89Y
1/T1 arises from excitations out of a spinon Fermi surface. Our findings lend
credence to the theoretical suggestion [G. Chen, R. Pereira, and L. Balents,
Phys. Rev. B 82, 174440 (2010)] that strong spin-orbit coupling can enhance
quantum fluctuations and lead to a QSL state in the double perovskite lattice.Comment: 6 pages 5 figure
Spin-gap behaviour in the 2-leg spin-ladder BiCu2PO6
We present magnetic suscceptibility and heat capacity data on a new S=1/2
two-leg spin ladder compound BiCu2PO6. From our susceptibility analysis, we
find that the leg coupling J1/k_B is ~ 80 K and the ratio of the rung to leg
coupling J2/J1 ~ 0.9. We present the magnetic contribution to the heat capacity
of a two-leg ladder. The spin-gap Delta/k_B =3 4 K obtained from the heat
capacity agrees very well with that obtained from the magnetic susceptibility.
Significant inter-ladder coupling is suggested from the susceptibility
analysis. The hopping integrals determined using Nth order muffin tin orbital
(NMTO) based downfolding method lead to ratios of various exchange couplings in
agreement with our experimental data. Based on our band structure analysis, we
find the inter-ladder coupling in the bc-plane J2 to be about 0.75J1 placing
the compound presumably close to the quantum critical limit.Comment: 8 pages, 5 figure
Sc2Ga2CuO7: A possible quantum spin liquid near the percolation threshold
Sc2Ga2CuO7 (SGCO) crystallizes in a hexagonal structure (space group: P63/mmc), which can be seen as an alternating
stacking of single and double triangular layers. Combining neutron, x-ray, and resonant x-ray diffraction we establish that
the single triangular layers are mainly populated by non-magnetic Ga3+ ions (85% Ga and 15% Cu), while the bi-layers have comparable population of Cu2+ and Ga3+ ions (43% Cu and 57% Ga). Our susceptibility measurements in the temperature range 1.8 - 400 K give no indication of any spin-freezing or magnetic long-range order (LRO).We infer an effective paramagnetic moment μeff = 1.79±0.09 μB and a Curie-Weiss temperature �CW of about −44 K, suggesting antiferromagnetic interactions between the Cu2+(S = 1/2) ions. Low-temperature neutron powder diffraction data showed no evidence for LRO down to 1.5
K. In our specific heat data as well, no anomalies were found down to 0.35 K, in the field range 0-140 kOe. The magnetic
specific heat, Cm, exhibits a broad maximum at around 2.5 K followed by a nearly power law Cm/ T� behavior at lower
temperatures, with � increasing from 0.3 to 1.9 as a function of field for fields upto 90 kOe and then remaining at 1.9 for fields
upto 140 kOe. Our results point to a disordered ground state in SGCO
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