4,662 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
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Existence Of The Magnetorotational Instability
By posing and solving a global axisymmetric eigenvalue problem on an infinite domain with modes vanishing at zero and infinity for a differentially rotating MHD plasma, the conditions for the occurrence of a purely growing low-frequency mode known as the magnetorotational instability (MRI) are mapped. It is shown that the MRI criterion drawn from the "local dispersion relation" is at best inadequate and may even be misleading. The physics of the MRI is rather nuanced. It is dictated by the details of the radial profile of the rotation velocity Omega(r) and not just by the sign and the magnitude of its gradient, Omega'. The salient features of the class of profiles for which the MRI-like eigenmodes may occur are given along with the eigenspectrum. For a variety of other profiles, it is shown that an unstable magnetorotational mode is not a valid eigensolution.Institute for Fusion Studie
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
Semi-empirical model for prediction of unsteady forces on an airfoil with application to flutter
A semi-empirical model is described for predicting unsteady aerodynamic forces on arbitrary airfoils under mildly stalled and unstalled conditions. Aerodynamic forces are modeled using second order ordinary differential equations for lift and moment with airfoil motion as the input. This model is simultaneously integrated with structural dynamics equations to determine flutter characteristics for a two degrees-of-freedom system. Results for a number of cases are presented to demonstrate the suitability of this model to predict flutter. Comparison is made to the flutter characteristics determined by a Navier-Stokes solver and also the classical incompressible potential flow theory
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