Magnetocaloric Features Research Articles

Magnetocaloric features of complex molecular magnets: The (Cr 7Ni) 2Cu molecular magnet and beyond

We study the new kind of systems represented by the Cr 7Ni–M–Cr 7Ni (M=Cu +2) molecule, which is a promising molecular achievement from the perspective of molecular electronics. By using an effective quantum Hamiltonian, an exact calculation of the magnetic specific heat C Mag and the magnetocaloric features, namely, the adiabatic change of the entropy Δ S Mag and temperature Δ T ad , respectively, are developed. A systematic simulation of the magnetocaloric properties is generated by modifying the effective exchange couplings into the molecular system. Extended discussion of calculated magnetocaloric features and its possible realization by experimental methods, are performed. In addition, comparisons with an exact numerical result and with a Van Vleck transformation, which has important application in similar micromagnetic structures with no exact analytical solution and larger Hilbert space, are presented. Moreover, an expression for the entangling-excitation frequencies of these systems is given as first application of our simplified solution to the effective molecular Hamiltonian.

Improvement of refrigerant capacity of La0.67Ca0.33MnO3 single crystal with a few percent Fe doping

Large low-field-induced magnetic entropy changes, Delta S (M), are observed in La0.67Ca0.33MnO3 and La0.67Ca0.33Mn0.96Fe0.04O3 single crystals. The peaks of Delta S (M) broadened asymmetrically to high temperatures under higher magnetic fields for two materials should be attributed to the first-order magnetic phase transition at T (c). A small amount of iron doping results in an increase in the refrigerant capacity of the material though the magnetic entropy change decreases. The discovery of excellent magnetocaloric features of these single crystals in the low magnetic field can provide some ideas for exploring novel magnetic refrigerants operating under permanent magnet rather than superconducting one as magnetic field source.

Large magnetocaloric effect in Pr1−xPbxMnO3 (0.1⩽x⩽0.5) perovskites

This research reports the findings of large low-field magnetocaloric effect in polycrystalline Pr1−xPbxMnO3 (0.1⩽x⩽0.5) perovskites. It is found that, upon an applied field of 13.5kOe, the magnetic entropy change (ΔSM) reached values of 3.91, 3.68, and 3.34J∕kgK for x=0.1, 0.4, and 0.5 compositions, respectively. These values are larger than that of Gd (3.32J∕kgK) and were attained by a low applied magnetic field that can be generated by permanent magnets. These superior magnetocaloric features together with a relatively low material cost make the Pr1−xPbxMnO3 perovskites attractive candidate materials for magnetic refrigerators in a temperature range of 150–270K.