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 temperaturesSmall samples

(~1 mg)High

magnetic fields

Physical Properties Measuring System (PPMS)

Temperature1.9 a 400 K

Cost~ U$ 300k

Magnetic field H = 9 Tesla

Continuos operation with remote access 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008

0

5

10

15

20

Ghivelder e colaboradores outros pesquisadores

total - 125 papers

Núm

ero

de

publ

icaç

ões

Ano

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

• mm = molar magnetic susceptibility= molar magnetic susceptibility

• C C = Curie constant= Curie constant

• = Weiss constant= Weiss constant

mm = C/(T+ = C/(T+))

mm

mm

= 0 = 0 Paramagnetic - Paramagnetic - independent independent

spinsspins

> 0 > 0 Ferromagnetic interactions Ferromagnetic interactions

< 0 < 0 Antiferromagnetic Antiferromagnetic

interactionsinteractions

Ferromagnets and Antiferromagnets

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.10

0 100 200 300 400

Temperature (K)M

ola

r S

usc

epti

bili

ty,

m

Antiferromagnet

TN =100 K

TN

mm

non-frozen

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

0 100 200 300 400

Temperature (K)

Mo

lar

Su

scep

tib

ility

, m

Ferromagnet

TC =100 K(T=0) = 3 B

TC

mm

non-frozen

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

20 30 40 50 60 70 800

1

2

T (K)

M (

emu/

g)

Ni3AlH=1.5Oe

Field Cooled

Zero Field Cooled

An ordinary ferromagnet

Isolated FeNnanoparticlesH = 20 Oe

50 100 150

0.6

1.2

1.8

0

(

10-2

em

u/cm

3 )

T (K)

Isolated magnetic moments0 10 20 30 400.5

1.0

1.5

T (K)M

(10

-3 e

mu/

cm3 )

Cu97Mn3H= 1.0 Oe

Canonical Spin-Glass

Slow dynamics in spin glasses

Frequency dependence of the ac susceptibility

Hac= 1 Oe, Hdc= 0 Oe

Temperature (K)5 10 15 20 25 30

' (

emu/

mol

)

0

2

4

6

811 Hz33 Hz 110 Hz 333 Hz 1100 Hz3330 Hz11.0 kHz

Canonical Spin-Glass

0 50 100 150 200 250

0.00

0.05

0.10

0.15

0.20

0.25Au0.81Fe0.19

M (

emu/

g)

T(K)

ZFC

FC

H = 30 Oe

Re-entrant spin glasses

0 50 100 150 200

0

100

200

300

400 Au0.81Fe0.19 Tc (H)Tk (H)

R-SG

FM PM

H (

Oe

)

T (K)

Manganites

Research areas:

La1-xCaxMnO3

CMR

AFM

Phase Separation

Phase separation in La0.5Ca0.5MnO3

FM

AFM-CO

0 50 100 150 200 250 3000.00

0.01

0.02

0.03

0.04

0.05

0.06 La0.5

Ca0.5

MnO3

H = 20 Oe

M ( B

/Mn)

T (K) PMIFMM

AFM-COI

Tc

TN

PS

FM fraction depends on grain size of the polycrystalline sample

Structural determination with x-ray diffraction

Laboratório Nacional de Luz SincrotronLNLS – Campinas, São Paulo

X-ray powder diffraction measurements

high resolution

Data analysis with Rietveld refinment

20 40 60 80 100 120

-2000

-1000

0

1000

2000

3000

4000

5000

6000

7000 Yobs

Ycalc

Yobs

- Ycalc

Pos. Bragg

La0.225

Pr0.4

(Ca0.95

Sr0.05

)0,375

MnO3

In

tens

ity (

a.u.

)

deg

RB = 6.91 %

RF = 5.85 %

2 = 1.67

Evolution of Mn-O-Mn bond angle and Mn-O bond lenght with increasing Sr concentent

Results from Rietveld analysis

50 100 150 200 250 300

5.41

5.42

5.43

5.44

5.45

La0.225

Pr0.4

(Ca1-x

Srx)0,375

MnO3

x = 0.05

M-D

C (

emu/

g)

La

ttice

Par

amet

ers

(A)

Temperature (K)

a b´ c

0

5

10

15

20

x = 0.05

Capacitive DilatometerCapacitive Dilatometer

Magnetostriction and thermal expansion measurements

Magnetostriction and thermal expansion measurements

Experimental technique to proble volume changes in the compound

Experimental technique to proble volume changes in the compound

Volume reduction at the metamagnetic tansition

Resistivity relaxation after applying and removing Hdc

DYNAMICSDYNAMICS

AFM

time

H(to go faster)

La0.325Pr0.30Ca0.375MnO3

Double Perovskites with RuResearch areas:

20 25 30 35 400.3

0.4

0.5

0.6

0.7

0.8

Sr2YRuO6

C

/T (

J/m

ol.K

2 )

T (K)

Perovskites ABO3

Double perovskites A2BB’O6

Sr2YRuO6

Specific heat

100

150

153

156

159

162distance Ru-O2

angleY-O1-Ru

angleY-O2-Ru

5020 300

Y-O

-Ru

angl

es (

degr

ees)

T (K)

1.8

1.9

2.0

2.1

2.2

Ru-

O2

dis

tanc

e (Å

)

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

Sr2YRuO6

Magnetocaloric materials

Research areas:

Prof. Angelo Gomes

Superconductivity

Research areas:

Prof. Said Sugui

The Discovery

Type II superconductors

Mixedstate

Normalstate

Meissnerstate

H

T

Hc2

(T=0)

Hc1 (T=0)

Tc (H=0)

VorticesVortices

Magnetization of a type II superconducor

YBa2Cu3O7-

High temperature superconductors

Materials:Materials:

YBa2Cu3O7-

Very complex physics

Measurement made at Imperial College, UK, with scanning tunneling

microscopy

Ba1-xKxFe2As2

Discovered in 2008 : New Fe and As based superconductorsPinictides

Large number of pinictides compounds discovered so far

BaFe1.8Co0.2As2 is predicted to have an upper critical field of 43 Teslas

Some experimetal results

YBaCuOYBaCuO

88 89 90 91 92 93 94

-0.8

-0.6

-0.4

-0.2

0.0

f = 500 Hz

hac=0.5 Oe

' (a

.u.)

T (K)

91.6 91.8 92.0 92.2 92.4 92.6 92.8 93.0

-0.8

-0.6

-0.4

-0.2

0.0

f = 500 Hz

hac=0.5 Oe

' (a

.u.)

T (K)

0 2 4 6 8

-0.04

-0.02

0.00 T = 60 K

full penetration field

Hp - 2nd magnetizarion peak

m (e

.m.u

)

H (T)

0 2 4 6 8

-0.04

-0.02

0.00

m (e

.m.u

)

H (T)

dm/d(log(t))

El Laboratorio de Bajas TemperaturasEl Laboratorio de Bajas Temperaturas

PPMSPPMS

VSMVSM

SQUIDSQUID

Mili KelvinMili Kelvin

Preparación de

materiales

Helio liquidoHelio liquido

Postgrado en la Universidad Federal de Río de Janeiro

Becas para maestría y doctorado accesible

Gracias