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

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

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

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

Magnetization

Resistivity Specific heat

Software control

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

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

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

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

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

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

Re-entrant spin glasses

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

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

FM fraction depends on grain size of the polycrystalline sample

Structural determination with x-ray diffraction

Laboratório Nacional de Luz Sincrotron LNLS – Campinas, São Paulo

X-ray powder diffraction measurements high resolution

Data analysis with Rietveld refinment

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

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

Volume reduction at the metamagnetic tansition

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

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

Neutron diffraction for determining structure and magnetism

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

Magnetocaloric materials Research areas: Prof. Angelo Gomes

Superconductivity Research areas: Prof. Said Sugui

The Discovery

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

Magnetization of a type II superconducor

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

YBa 2 Cu 3 O 7-  Very complex physics

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

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

Some experimetal results YBaCuO

El Laboratorio de Bajas Temperaturas PPMS

VSM SQUID Mili Kelvin

Preparación de materiales

Helio liquido

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

Gracias