3,824 research outputs found
Frustration induced disordered magnetism in Ba3RuTi2O9
The title compound Ba3RuTi2O9 crystallizes with a hexagonal unit cell. It
contains layers of edge shared triangular network of Ru4+ (S=1) ions. Magnetic
susceptibility chi(T) and heat capacity data show no long range magnetic
ordering down to 1.8K. A Curie-Weiss (CW) fitting of chi(T) yields a large
antiferromagnetic CW temperature theta_CW=-166K. However, in low field, a
splitting of zero field cooled (ZFC) and field cooled (FC) chi(T) is observed
below ~30K. Our measurements suggest that Ba3RuTi2O9 is a highly frustrated
system but only a small fraction of the spins in this system undergo a
transition to a frozen magnetic state below ~30K.Comment: 5 pages, 6 figures (accepted in EPJB
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
Tunable temperature induced magnetization jump in a GdVO3 single crystal
We report a novel feature of the temperature induced magnetization jump
observed along the a-axis of the GdVO3 single crystal at temperature TM = 0.8
K. Below TM, the compound shows no coercivity and remanent magnetization
indicating a homogenous antiferromagnetic structure. However, we will
demonstrate that the magnetic state below TM is indeed history dependent and it
shows up in different jumps in the magnetization only when warming the sample
through TM. Such a magnetic memory effect is highly unusual and suggesting
different domain arrangements in the supposedly homogenous antiferromagnetic
phase of the compound.Comment: 17 pages, 8 Figure
BaV3O8: A possible Majumdar-Ghosh system with S=1/2
BaV3O8 contains both magnetic V4+(S=1/2) ions and non-magnetic V5+(S=0) ions.
The V4+ ions are arranged in a coupled Majumdar-Ghosh chain like network. Our
magnetic susceptibility chi(T) data fit well with the Curie-Weiss formula in
the temperature range of 80-300K and it yields a Curie constant
C=0.39cm3K/mole-V4+ and an antiferromagnetic Weiss temperature theta=-26K. The
chi(T) curve shows a broad maximum at T~25K indicative of short-range order
(SRO) and an anomaly corresponding to long-range order (LRO) at TN~6K. The
value of the frustration index (f=mod[theta/TN]~5) suggests that the system is
moderately frustrated. Above the LRO temperature the experimental magnetic
susceptibility data match well with the coupled Majumdar-Ghosh chain model with
the ratio of the nnn (next-nearest neighbor) to nn (nearest neighbor) magnetic
coupling alpha=2 and Jnnn/kB=40K. In a mean-field approach when considering the
inter-chain interactions, we obtain the total inter-chain coupling to be about
16K. The LRO anomaly at TN is also observe in the specific heat Cp(T) data and
is not sensitive to an applied magnetic field up to 90kOe. A 51V NMR signal
corresponding to the non-magnetic vanadium was observed. Anomalies at 6K were
observed in the variation with temperature of the 51V NMR linewidth and in the
spin-lattice relaxation rate 1/T1, indicating that they are sensitive to the
LRO onset and fluctuations at the magnetic V sites. The existence of two
components (one short and another long) is observed in the spin-spin relaxation
rate 1/T2 data in the vicinity of TN. The shorter component seems to be
intimately connected with the magnetically ordered state. We suggest that both
magnetically ordered and non-long range ordered (non-LRO) regions coexist in
this compound below the long range ordering temperature.Comment: Accepted in Phys. Rev.
89Y NMR Probe of Zn Induced Local Magnetism in YBa2(Cu(1-y)Zn(y))3O(6+x)
We present detailed data and analysis of the effects of Zn substitution on
the planar Cu site in YBaCuO (YBCO) as evidenced from
our Y NMR measurements on oriented powders. For we find
additional NMR lines which are associated with the Zn substitution. From our
data on the intensities and temperature dependence of the shift, width, and
spin-lattice relaxation rate of these resonances, we conclude that the spinless
Zn 3 state induces local moments on the near-neighbour () Cu
atoms. Additionally, we conjecture that the local moments actually extend to
the farther Cu atoms with the magnetization alternating in sign at subsequent
sites. We show that this analysis is compatible with ESR data taken on
dilute Gd doped (on the Y site) and on neutron scattering data reported
recently on Zn substituted YBCO. For optimally doped compounds
Y resonances are not detected, but a large % -dependent
contribution to the Y NMR linewidth is evidenced and is also attributed
to the occurence of a weak induced local moment near the Zn. These results are
compatible with macroscopic magnetic measurements performed on YBCO
samples prepared specifically in order to minimize the content of impurity
phases. We find significant differences between the present results on the
underdoped YBCO samples and Al NMR data taken on Al
substituted on the Cu site in optimally doped LaCuO. Further
experimental work is needed to clarify the detailed evolution of the impurity
induced magnetism with hole content in the cuprates.Comment: To be published in EPJB 15 pages of text and figures in eps forma
75As NMR local probe study of magnetism in (Eu1-xKx)Fe2As2
75As NMR measurements were performed as a function of temperature and doping
in (Eu1-xKx)Fe2As2 (x=0,0.38,0.5,0.7) samples. The large Eu2+ moments and their
fluctuations are found to dominate the 75As NMR properties. The 75As nuclei
close to the Eu2+ moments likely have a very short spin-spin relaxation time
(T2) and are wiped out of our measurement window. The 75As nuclei relatively
far from Eu2+ moments are probed in this study. Increasing the Eu content
progressively decreases the signal intensity with no signal found for the
full-Eu sample (x=0). The large 75As NMR linewidth arises from an inhomogeneous
magnetic environment around them. The spin lattice relaxation rate (1/T1) for
x=0.5 and 0.7 samples is nearly independent of temperature above 100K and
results from a coupling to paramagnetic fluctuations of the Eu2+ moments. The
behavior of 1/T1 at lower temperatures has contributions from the
antiferromagnetic fluctuations of the Eu2+ moments as also the fluctuations
intrinsic to the FeAs planes and from superconductivity.Comment: 6 pages, 6 figures (to appear in EPJB
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