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Study of the magnetocaloric effect in intermetallic compounds


The objective of this project is the study of polycrystalline, monocrystalline samples, as well as thin films, of alloys and intermetallic compounds presenting the magnetocaloric effect, paying particular attention to effects of crystal field and quadrupolar interactions, anisotropy of the exchange energy and magnetoelastic effects. We have particular interest in materials presenting first order magnetic transitions and low Debye temperatures 8D. Also we have great interest in the variation of 8D and of the magnetic properties under absorption of interstitial elements as H, N and C. The magnetoelastic effects will be characterized through measurements of magnetoestriction and elastic constants without and with applied field. An important feature of this project is that, for a given material, the samples to be used in the several characterization techniques will come from the same master alloy, obtained and characterized in our laboratory, avoiding ambiguities arising from different materials and preparation procedures. The specific materials will be theoretically modeled, and the results of such models will be compared with the whole set of experimental data, what will validate the models or suggest ways for their modification. This will also allow to obtain the several parameters of interest for the models, as the crystal field parameters and the magnetoelastic coupling constants. This project joins 4 research groups from Unicamp (GPCM, LDRX, LML and LPP), one group from CBPF and another from UERJ. The activities of all groups will be complementary. Chosen a given material, it will be synthesized in polycrystalline form by some convenient process, and then characterized structurally and magnetically. If possible through our technical means, a single crystal will be grown, and then a full characterization of the material will be obtained measuring the properties along the crystalline directions. Again, the experimental results will be compared to the results of a model. Besides this, the material can be obtained in thin film form, and characterized, or can be obtained as a dispersed nanocomposite in a non-magnetic matrix, and also characterized. With a view in technological applications, careful attention will be paid to materials presenting magnetic first order transitions, mainly when they are coupled to other kind of transformations, as the structural ones. This study will allow a selection of materials adequate to technical applications, mainly in the magnetic refrigeration field (but also in the sensor area), around roam temperature or at low temperature, where the main interest is in the economic generation of cryogenic liquids. The specific materials to be studied in this project are: the system Gd-Ge-Si, the system Fe- Rh, the Laves phases of the family RAl2 (R = rare earth), the intermetallic compounds of the R-Co family, the intermetallic compounds YbAs and YbN, and some compositions of the manganite ceramics. Other materials will be studied, depending on the group's interest. In order to turn the project viable, some key instruments are asked to be financed, as a PPMS system to the measurements of specific heat under magnetic field, a varitemp cryostat and related equipments for the assembling of the magnetostriction measuring facility and of the elastic constants facility, besides the assembling of a high vacuum chamber for thin films deposition using three magnetron electrodes. Other equipments are asked in order to allow other kinds of characterizations. (AU)

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Scientific publications
(References retrieved automatically from Web of Science and SciELO through information on FAPESP grants and their corresponding numbers as mentioned in the publications by the authors)
GAMA‚ S.; COELHO‚ A.A.; DE CAMPOS‚ A.; CARVALHO‚ A.M.G.; GANDRA‚ F.C.G.; VON RANKE‚ P.J.; DE OLIVEIRA‚ N.A.. Pressure-induced colossal magnetocaloric effect in MnAs. Physical Review Letters, v. 93, n. 23, p. 237202, . (01/05883-0)
DE CAMPOS, A.; MOTA, M. A.; GAMA, S.; COELHO, A. A.; WHITE, B. D.; DA LUZ, M. S.; NEUMEIER, J. J.. Single crystal growth and characterization of MnAs. Journal of Crystal Growth, v. 333, n. 1, p. 54-58, . (01/05883-0, 05/04681-6)

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