314 research outputs found
Magnetocaloric effect in nano- and polycrystalline manganite
samples were prepared in nano- and polycrystalline
forms by sol-gel and solid state reaction methods, respectively, and
structurally characterized by synchrotron X-ray diffraction. The magnetic
properties determined by ac susceptibility and dc magnetization measurements
are discussed. The magnetocaloric effect in this nanocrystalline manganite is
spread over a broader temperature interval than in the polycrystalline case.
The relative cooling power of the poly- and nanocrystalline manganites is used
to evaluate a possible application for magnetic cooling below room temperature.Comment: 6 pages, 5 (double) figures, 1 table, 16 references; submitted to
Appl. Phys.
Asymmetry of the latent heat signature in b-axis oriented single crystal Gd Si Ge
A 100 micron fragment of a b-axis oriented single crystal Gd Si Ge has been studied using microcalorimetry, enabling the separate measurement of the heat capacity and the latent heat. The sample was taken from the same crystal previously studied with Hall probe imaging, which showed that the phase transition is seeded by a second phase of Gd Si Ge nanoplatelets on the increasing field sweep direction only. The multiple transition features observed in the latent heat signature suggests a nucleation size of approximately 20 μm, consistent with the lengthscale suggested by Hall imaging. The difference in nucleation and growth process with field sweep direction is clearly identified in the latent heat. We show that the latent heat contribution to the entropy change is of the order of 50% of the total entropy change and unlike other systems studied, the transition does not broaden (and the latent heat contribution does not diminish significantly) as magnetic field and temperature are increased within the parameter range explored in these experiments
Specific heat study of single crystalline Pr Ca MnO in presence of a magnetic field
We present the results of a study of specific heat on a single crystal of
PrCaMnO performed over a temperature range 3K-300K in
presence of 0 and 8T magnetic fields. An estimate of the entropy and latent
heat in a magnetic field at the first order charge ordering (CO) transition is
presented. The total entropy change at the CO transition which is 1.8
J/mol K at 0T, decreases to 1.5 J/mol K in presence of 8T magnetic
field. Our measurements enable us to estimate the latent heat
235 J/mol involved in the CO transition. Since the entropy of the
ferromagnetic metallic (FMM) state is comparable to that of the charge-ordered
insulating (COI) state, a subtle change in entropy stabilises either of these
two states. Our low temperature specific heat measurements reveal that the
linear term is absent in 0T and surprisingly not seen even in the metallic FMM
state.Comment: 8 pages (in RevTEX format), 12 figures (in postscript format)
Submitted to Phys. Rev.
Energy spectrum of a 2D Dirac electron in the presence of a constant magnetic field
In this paper we obtain exact solutions of a 2D relativistic Dirac oscillator
in the presence of a constant magnetic field. We compute the energy spectrum
and discuss its dependence on the spin and magnetic field strength.Comment: 7 page
Magnetocaloric effect in spin-1/2 chains with three-spin interactions
We consider the exactly solvable spin-1/2 chain with the three-spin
interactions of the and types in an external (transverse)
magnetic field. We calculate the entropy and examine the magnetocaloric effect
for the quantum spin system. We discuss a relation between the cooling/heating
efficiency and the ground-state phase diagram of the quantum spin model. We
also compare ability to cool/heat in the vicinity of the quantum critical and
triple points. Moreover, we examine the magnetocaloric effect for the spin-1/2
chain with three-spin interactions in a random (Lorentzian) transverse
magnetic field.Comment: 10 pages, 8 figure
Overview of the Characteristic Features of the Magnetic Phase Transition with Regards to the Magnetocaloric Effect: the Hidden Relationship Between Hysteresis and Latent Heat
This article was published in the journal, Metallurgical and Materials Transactions E [Springer / © The Minerals, Metals & Materials Society and ASM International]. The final publication is available at Springer via http://dx.doi.org/10.1007/s40553-014-0015-8The magnetocaloric effect has seen a resurgence in interest over the last 20 years as a means towards an alternative energy efficient cooling method. This has resulted in a concerted effort to develop the so-called “giant” magnetocaloric materials with large entropy changes that often come at the expense of hysteretic behavior. But do the gains offset the disadvantages? In this paper, we review the relationship between the latent heat of several giant magnetocaloric systems and the associated magnetic field hysteresis. We quantify this relationship by the parameter Δμ 0 H/ΔS L, which describes the linear relationship between field hysteresis, Δμ 0 H, and entropy change due to latent heat, ΔS L. The general trends observed in these systems suggest that itinerant magnets appear to consistently show large ΔS L accompanied by small Δμ 0 H (Δμ 0 H/ΔS L = 0.02 ± 0.01 T/(J K−1 kg−1)), compared to local moment systems, which show significantly larger Δμ 0 H as ΔS L increases (Δμ 0 H/ΔS L = 0.14 ± 0.06 T/(J K−1 kg−1))
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