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Abstract
The structure and magnetic properties were comparatively analyzed for (Gd/Ti)n multilayers with Gd layer thickness of 1.5 to 12 nm. Multilayers were deposited by sputtering technique at room temperature and annealed for the temperatures up to 400 oC. It was observed that the samples are highly textured in a different way depending on the Gd layer thickness and annealing temperature. It was found that the heat treatment practically does not change the Gd grain size. The lattice parameters obtained from X-ray results change significantly only for (Gd(1.5nm)/Ti)50 multilayers, but their values remain higher than for the bulk Gd. The initial slope of the temperature dependence of magnetization near Curie temperature becomes steeper and Curie temperature increases upon annealing. Curie temperature variation can be understood by taking into account both relaxation of the lattice imperfections and change in lattice constants.
Highlights
Magnetic properties of nanostructured ferromagnetic materials show strong dependence on the microstructure [1]
The common way to characterize the magnetocaloric effect of a magnetic material is the relative cooling power (RCP), which is defined as the product of the maximum isothermal entropy change, !Smag(T,H), during the magnetization process, and the corresponding full-width-at-halfmaximum ("TFWHM), and Curie temperature (TC), which establishes the optimal operating temperature [5]
The practical utility of using the average nanocrystallite size and size distribution as control parameters to tune the magnetocaloric effect was recently demonstrated: the isothermal change in magnetic entropy at TC caused by an applied magnetic field is greater in bulk ferromagnets than in their nanocrystalline counterparts
Summary
Magnetic properties of nanostructured ferromagnetic materials show strong dependence on the microstructure [1]. In terms of the magnetocaloric effect, the TC value, and the magnitude of the derivative of the magnetization with respect to temperature at a constant magnetic field near TC is very important [7] It is known, that Curie temperature of nanocrystalline gadolinium depends on the grain size and annealing is an effective way to change the grain size and TC as a consequence [8]. In this work the structure and magnetic properties were comparatively analyzed for [Gd/Ti]n nanoscale multilayers prepared by dc magnetron sputtering
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