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Magnetismo y Superconductividad: Principios fundamentales, sistemas experimentales y líneas de investigación en el laboratorio de bajas temperaturas Luis.

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Presentation on theme: "Magnetismo y Superconductividad: Principios fundamentales, sistemas experimentales y líneas de investigación en el laboratorio de bajas temperaturas Luis."— Presentation transcript:

1 Magnetismo y Superconductividad: Principios fundamentales, sistemas experimentales y líneas de investigación en el laboratorio de bajas temperaturas Luis Ghivelder Instituto de Física Universade Federal do Rio de Janeiro Colombia - abril 2013

2 Experimental techniques Some research areas Manganites Double perovskites Superconductivity Magnetization Specific heat Resistivity Magnetostriction x-ray diffraction neutron diffraction sample preparation Magnetocaloric materials

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

4 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

5 Magnetization

6 Resistivity Specific heat

7 Software control

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

9 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

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

11 Other types of magnetic ordering: Spin glass and cluster glass states Spins or magnetic moments frozen in a disordered state Frustration of magnetic interactions due to disorder

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

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

14 Re-entrant spin glasses

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

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

17 FM fraction depends on grain size of the polycrystalline sample

18 Structural determination with x-ray diffraction

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

20 X-ray powder diffraction measurements high resolution

21 Data analysis with Rietveld refinment

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

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

24 Volume reduction at the metamagnetic tansition

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

26 Double Perovskites with Ru Research areas: Perovskites  ABO 3 Double perovskites  A 2 BB’O 6 Sr 2 YRuO 6 Specific heat

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28 Neutron diffraction for determining structure and magnetism

29 Neutron diffraction data Combined neutron and x-ray diffraction yield a microscopic determination of the structure and magnetic phases Sr 2 YRuO 6

30 Magnetocaloric materials Research areas: Prof. Angelo Gomes

31 Superconductivity Research areas: Prof. Said Sugui

32 The Discovery

33 Type II superconductors Mixed state Normal state Meissner state H T H c2 (T=0) H c1 (T=0) T c (H=0) Vortices

34 Magnetization of a type II superconducor

35 YBa 2 Cu 3 O 7- High temperature superconductors Materials:

36 YBa 2 Cu 3 O 7-  Very complex physics

37 Measurement made at Imperial College, UK, with scanning tunneling microscopy Ba 1-x K x Fe 2 As 2 Discovered in 2008 : New Fe and As based superconductors Pinictides

38 Large number of pinictides compounds discovered so far BaFe 1.8 Co 0.2 As 2 is predicted to have an upper critical field of 43 Teslas

39 Some experimetal results YBaCuO

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42 El Laboratorio de Bajas Temperaturas PPMS

43 VSM SQUID Mili Kelvin

44 Preparación de materiales

45 Helio liquido

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

47 Gracias

48


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