  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.
