13 research outputs found
Application of the finite-temperature Lanczos method for the evaluation of magnetocaloric properties of large magnetic molecules
We discuss the magnetocaloric properties of gadolinium containing magnetic
molecules which potentially could be used for sub-Kelvin cooling. We show that
a degeneracy of a singlet ground state could be advantageous in order to
support adiabatic processes to low temperatures and simultaneously minimize
disturbing dipolar interactions. Since the Hilbert spaces of such spin systems
assume very large dimensions we evaluate the necessary thermodynamic
observables by means of the Finite-Temperature Lanczos Method.Comment: 7 pages, 10 figures, invited for the special issue of EPJB on "New
trends in magnetism and magnetic materials
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))
Who discovered the magnetocaloric effect?:Warburg, Weiss, and the connection between magnetism and heat
A magnetic body changes its thermal state when subjected to a changing magnetic field. In
particular, if done under adiabatic conditions, its temperature changes. For the past 15
years the magnetocaloric effect has been the focus of significant research due to its
possible application for efficient refrigeration near room temperature. At the same time,
it has become common knowledge within the magnetic refrigeration research community that
the magnetocaloric effect was discovered by the German physicist E. Warburg in 1881. We
re-examine the original literature and show that this is a misleading reading of what
Warburg did, and we argue that the discovery of the effect should instead be attributed to
P. Weiss and A. Piccard in 1917
Cooling of a Fermi quantum plasma
We propose an adiabatic magnetization process for cooling a Fermi electron gas to ultra-low temperatures as an alternative to the known adiabatic demagnetization mechanism. We show via a new adiabatic equation that at the constant density the increase of the magnetic field leads to the temperature decrease as T ~ 1/H2. This process is identified in our numerical calculations, in which we also recover the adiabatic demagnetization mechanism for certain range