Tailoring the magnetocaloric effect in oxides

Searching for new magnetocaloric materials with significant magnetic entropy change over a wide temperature range, we combine magnetic oxides with different transition temperatures. We use pulsed laser deposition (PLD) technique to growth bilayer and trilayer composites of two different oxides La₂NiMnO₆ (LNMO) and La_2/3Sr_1/3MnO₃ (LSMO) on LSAT substrates. In bilayer samples, we can affect the ratio of the cation ordering in LNMO layer by changing the arrangement of the layers. We get a cation-ordered LNMO layer with a magnetic phase transition at 230 K when it is deposited on a bare substrate. However, it shows a lower magnetic phase transition temperature at 180 K when it is grown on top a LSMO. This behavior driven by strains can be used in trilayer samples where three magnetic transition can be detected, enabling us to get a roughly temperature-independent table-top magnetic entropy change over a temperature range as large as 100 K. These results suggest a route through composites to tune the magnitude, shape and width of the temperature dependence of the magnetic entropy change. This technique allows us to tailor an appropriate material for magnetic refrigeration at room temperature by changing the arrangement of layers.