114 research outputs found
The Tightness of the Kesten-Stigum Reconstruction Bound of Symmetric Model with Multiple Mutations
It is well known that reconstruction problems, as the interdisciplinary
subject, have been studied in numerous contexts including statistical physics,
information theory and computational biology, to name a few. We consider a
-state symmetric model, with two categories of states in each category,
and 3 transition probabilities: the probability to remain in the same state,
the probability to change states but remain in the same category, and the
probability to change categories. We construct a nonlinear second order
dynamical system based on this model and show that the Kesten-Stigum
reconstruction bound is not tight when .Comment: Accepted, to appear Journal of Statistical Physic
Magnetocaloric effect and nature of magnetic transition in nanoscale Pr0.5Ca0.5MnO3
Systematic measurements pertinent to the magnetocaloric effect and nature of
magnetic transition around the transition temperature are performed in the 10
nm Pr0.5Ca0.5MnO3 nanoparticles (PCMO10) . Maxwell relation is employed to
estimate the change in magnetic entropy. At Curie temperature TC, 83.5 K, the
change in magnetic entropy discloses a typical variation with a value 0.57 J/kg
K, and is found to be magnetic field dependent. From the area under the curve
Delta S vs T, the refrigeration capacity is calculated at TC, 83.5 K and it is
found to be 7.01 J/kg. Arrott plots infer that due to the competition between
the ferromagnetic and anti ferromagnetic interactions, the magnetic phase
transition in PCMO10 is broadly spread over both in temperature as well as in
magnetic field coordinates. Upon tuning the particle size, size distribution,
morphology, and relative fraction of magnetic phases, it may be possible to
enhance the magnetocalorific effect further in PCMO10.Comment: Accepted (Journal of Applied Physics) (In press
Martensite-like transition and spin-glass behavior in nanocrystalline Pr0.5Ca0.5MnO3
We report on isothermal pulsed (20 ms) field magnetization, temperature
dependent AC - susceptibility, and the static low magnetic field measurements
carried out on 10 nm sized Pr0.5Ca0.5MnO3 nanoparticles (PCMO10). The
saturation field for the magnetization of PCMO10 (~ 250 kOe) is found to be
reduced in comparison with that of bulk PCMO (~300 kOe). With increasing
temperature, the critical magnetic field required to 'melt' the residual
charge-ordered phase decays exponentially while the field transition range
broadens, which is indicative of a Martensite-like transition. The AC -
susceptibility data indicate the presence of a frequency-dependent freezing
temperature, satisfying the conventional Vogel-Fulcher and power laws, pointing
to the existence of a spin-glass-like disordered magnetic phase. The present
results lead to a better understanding of manganite physics and might prove
helpful for practical applications
Oscillatory exchange bias and training effects in nanocrystalline Pr0.5Ca0.5MnO3
We report on exchange bias effects in 10 nm particles of Pr0.5Ca0.5MnO3 which
appear as a result of competing interactions between the ferromagnetic
(FM)/anti-ferromagnetic (AFM) phases. The fascinating new observation is the
demonstration of the temperature dependence of oscillatory exchange bias (OEB)
and is tunable as a function of cooling field strength below the SG phase, may
be attributable to the presence of charge/spin density wave (CDW/SDW) in the
AFM core of PCMO10. The pronounced training effect is noticed at 5 K from the
variation of the EB field as a function of number of field cycles (n) upon the
field cooling (FC) process. For n > 1, power-law behavior describes the
experimental data well; however, the breakdown of spin configuration model is
noticed at n \geq 1
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