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Published byRoss Merritt Modified about 1 year ago

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Experimental Techniques Magnetization Specific heat Resistivity Low temperatures Small samples (~1 mg) High magnetic fields

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Physical Properties Measuring System (PPMS) Temperature 1.9 a 400 K Cost ~ U$ 300k Magnetic field H = 9 Tesla Continuos operation with remote access main experimental system

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Magnetization

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Resistivity Specific heat

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Software control

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Review - Magnetism in solids Principios fundamentales Temperature induced disorder Longe range order

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weakly interacting electrons the Curie-Weiss law Paramagnets m = molar magnetic susceptibility m = molar magnetic susceptibility C = Curie constant C = Curie constant = Weiss constant = Weiss constant m = C/(T+ ) mmmm m = 0 Paramagnetic - independent spins > 0 Ferromagnetic interactions < 0 Antiferromagnetic interactions

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Ferromagnets and Antiferromagnets mmmm non-frozen mmmm

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Sometimes it is difficult to distinguish experimentally between different magnetic states An ordinary ferromagnet Isolated magnetic moments Canonical Spin-Glass

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Slow dynamics in spin glasses Frequency dependence of the ac susceptibility Canonical Spin-Glass

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Manganites Research areas: La 1-x Ca x MnO 3 CMR AFM Phase Separation

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Phase separation in La 0.5 Ca 0.5 MnO 3 FM AFM-CO PMI FMM AFM-COI Tc TNTN PS

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FM fraction depends on grain size of the polycrystalline sample

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Structural determination with x-ray diffraction

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Laboratório Nacional de Luz Sincrotron LNLS – Campinas, São Paulo

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X-ray powder diffraction measurements high resolution

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Data analysis with Rietveld refinment

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Evolution of Mn-O-Mn bond angle and Mn-O bond lenght with increasing Sr concentent Results from Rietveld analysis x = 0.05

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Capacitive Dilatometer Magnetostriction and thermal expansion measurements Experimental technique to proble volume changes in the compound

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Volume reduction at the metamagnetic tansition

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Resistivity relaxation after applying and removing Hdc DYNAMICS AFM time H (to go faster) La Pr 0.30 Ca MnO 3

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Magnetocaloric materials Research areas: Prof. Angelo Gomes

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El Laboratorio de Bajas Temperaturas PPMS

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VSM SQUID Mili Kelvin

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Preparación de materiales

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Helio liquido

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Postgrado en la Universidad Federal de Río de Janeiro Becas para maestría y doctorado accesible

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Resistivity

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The solid state refrigeration process (1) Sample at ambient temperature and magnetically disordered. (2) Sample orders in applied magnetic field: magnetic entropy ( SM) decreases forcing other types of entropy to increase, and causing the sample to heat up. (3) Convective cooling process (sample in air or liquid). (4) Sample at ambient temperature but magnetically ordered. (5) Sample removed from applied field, disordered, cooler than ambient (1) (2)(3) (4) (5)

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Magnetic Entropy

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Magnetic refrigerator - Simple (in principle)

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