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

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Presentation on theme: "Experimental Techniques Magnetization Specific heat Resistivity Low temperatures Small samples (~1 mg) High magnetic fields."— Presentation transcript:

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

2 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

3 Magnetization

4 Resistivity Specific heat

5 Software control

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

7 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+  ) mmmm  m  = 0  Paramagnetic - independent spins  > 0  Ferromagnetic interactions  < 0  Antiferromagnetic interactions

8 Ferromagnets and Antiferromagnets mmmm non-frozen mmmm

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

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

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

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

13 FM fraction depends on grain size of the polycrystalline sample

14 Structural determination with x-ray diffraction

15 Laboratório Nacional de Luz Sincrotron LNLS – Campinas, São Paulo

16 X-ray powder diffraction measurements high resolution

17 Data analysis with Rietveld refinment

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

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

20 Volume reduction at the metamagnetic tansition

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

22 Magnetocaloric materials Research areas: Prof. Angelo Gomes

23 El Laboratorio de Bajas Temperaturas PPMS

24 VSM SQUID Mili Kelvin

25 Preparación de materiales

26 Helio liquido

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

28 Resistivity

29 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)

30 Magnetic Entropy

31 Magnetic refrigerator - Simple (in principle)


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