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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