Giant and reversible extrinsic magnetocaloric effects in La0.7Ca0.3MnO3 films due to strain

Large thermal changes driven by a magnetic field have been proposed for environmentally friendly energy efficient refrigeration, but only a few materials which suffer hysteresis show these giant magnetocaloric effects. Here we create giant and reversible extrinsic magnetocaloric effects in epitaxial films of the ferromagnetic manganite La0.7Ca0.3MnO3 using strain mediated feedback from BaTiO3 substrates near a first-order structural phase transition. Our findings should inspire the discovery of giant magnetocaloric effects in a wide range of magnetic materials, and the parallel development of nanostructured bulk samples for practical applications.Comment: 32 pages, 1 Table, 5 figures, supplementary informatio

Peculiar features of electron spin resonance spectra in (Ca,Na)-doped lanthanum manganites

The analysis of the ESR spectra for the powdered samples of (Ca,Na)-doped manganites have been performed in the temperature range 220–320 K. It is shown that the samples under investigation are characterized by a broadened para- to ferromagnetic transition and complicated spectra within the transitional region. The conclusion is made that the satisfactory interpretation of the resonance data is only possible if the interference of the coexisting phases is taken into account within the transitional region. Under these conditions, the resonance field for the paramagnetic phase is shown to increase with the temperature lowering, while that for the ferromagnetic phase first decreases and then approaches a value characteristic of the uniformly magnetized ferromagnetic sample. It is noted that the results obtained are in compliance with those predicted theoretically for the spherical particles containing a mixture of the paramagnetic and ferromagnetic phases