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2. Magnetic Instabilities

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Ranges of magnetic order detection (34 examples) Sereni, J ... evanescence. TN temp of ( T)/ T|max does not extrapolate to 0. Specific Heat of type-II systems ... – PowerPoint PPT presentation

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Title: 2. Magnetic Instabilities


1
2. Magnetic Instabilities -- Types of magnetic
phase boundaries
2
Ranges of magnetic order detection (34 examples)
Sereni, J Phys Soc Jpn 67 (1998) 1767
3
Sorting magnetic phase boundaries
Sereni, J.Phys.Soc.Jpn, 70 (2001) 2139
Type III TN nearly constant
Type II TN vanishes at finite temperature
Type I TN,C tarced down to 10 of TN,C (x 0)
4
Comparison of ordering temperature dependences
Ligand-doping
Magnetic field
Pressure
Inter-ligand substitution
J.Phys.Soc.Jpn, 70 (2001) 2139
5
2a. Physical properties of Type III systems
Exaempleary system hexagonal CePd2-xNixAl3
Sereni et al., PRB (2004) accepted Cond. Mat.
0303154-March 5.2004
6
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7
Lattice parameters
doping pressure
Inter-atomic distances
Ce -T spacing expands Ce -Al spacing contracts
For Ce-ligands spacing criteria see
Sereni et al., JMMM 140 (1995) 885. Handb.
Phys. Chem. RE, Vol 15, Ch 98 (1991)
8
High temperature properties T gtgtTN T ?CF
(crystal field splitting)
9
Magnetic Susceptibility
10
Crystal field Effects
Crystal Field Effect TK
11
Comparison between pressure and alloying effects
12
Scale of energy related to T?max (x, p) Measured
resistance
R(T) l/s ?o ?(T/?E) ?ph(T)
?E intensive parameter, better computed
from maximum curvature than T?max Best fit

R(T) Ro L tanh(T/?tgh) Rph(T)
Sereni et al., Cond. Mat. 0303154 - March
5th.2004
13
Comparison between concentration and pressure
dependence
14
Low temperature properties T TN (magn.
Order) T ltlt ?CF
15
Fermi Liquid (FL) vs Non-Fermi Liquid (NFL)
Conduction electron (Fermi gas - Sommerfeld)
Cel / T ? ?o ? ?ensity of states(?F) ? f (T)
(TltltT F) ?o ? ?o (Pauli susc.) ? ?A ( A
?/T2) Heavy quasiparticles (Fermi Liquid) Cel /
T f (T) ?(T) ? ?T (density of excitations) ?
?ensity of states(?F) ?(T?0) ? ? (T?0) ? ?A
(TltltTK) ? ?(T?0) Wilson ratio
Kadowaky-Woods First order corrections Cel / T ?
1- (T/To)2 ? ? 1 (T/To)2 ? ? A T 2 NFL
behavior Cel / T ?(T) ?T ? Logarithmic (Cel
/ T ? - Ln T) divergences ?(Cel / T)/ ?T ? 1/T
divergence ? Analytical Cel / T ?
1- ? T divergences No divergence in the Entropy
(S?Cp/T dT ) for T?0 ! ?(T) ? divergent for T?0
?(T) ? T Q (1.5 lt Q lt 2) or ? A (T) T 2
16
Expected behavior for 3D Antiferromagnetic
systems
  • ? T ?
  • ?0 -?(T/T0)

17
Pressure dependence of the exponent
? T n
18
Comparison between two concentrations
19
Magneto resistence
Scaling with field
20
Specific Heat at the LR-MO region
For x lt 0.2 T lt TN Cm / T ?0BT 2 B Jex
For x gt 0.2 broad maximum
21
Specific Heat at the critical concentration
Const.
?T scale
Cm / T ? ? - a?T
22
Normalized Entropy
Sereni Physica B 320 (2002) 376
T-scaling
23
Phase Diagram combining x and p
24
Conclusions for CePd2-x Nix Al3
  • Three regions in the magnetic phase diagram
  • 0 lt x lt 0.2 LR-MO (TN nearly independent of x
    )
  • 0.2 lt x lt 0.45 SR-Corr coexistence with NFL
    behavior ? Cm / T ? ?o (1 - ?T/D) D 18K
  • x 0.45 critical concentration
  • 0.4 lt x lt 0.9, exponent of ? ? T Q ? 1lt Q lt 2
  • x 0.9 onset of Fermi Liquid behavior (Q 2)

25
2b. Physical properties of Type II systems
(pressure induced superconductors)
26
Also for CePd2Si2 CeCu2 CeInGa3
Evanescent phase boundaries (Type II )
Rev.Esp de Fisica
Sereni, J.Phys.Soc.Jpn 70 (2001) 2139
27
Hydrostatical pressure
x2
28
CeCu2Si2 has a shaped superconducting phase
similar to pure Ce
? ?
? 6 9 12
15 Pure Ce
Wittig PRL 21 (1968) 1250
Holmes et al., PRB 69 (2004) 024508
29
Proof for LR-Order evanescence
TN ? temp of ?(?T)/?Tmax does not extrapolate to
0
30
Specific Heat of type-II systems
There is an entropy compensation respect to
Cp/T (T gtgt TN), extrapolated from the
paramagnetic state
31
Comparison of transition involving band states
ZrCe2
NpSn3
Pure itinerant magnetism Ref
Superconductor Sereni et al. Phill Mag Lett 68
(1993) 231
32
Entropy compensation
Magnetic free energy gain
33
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34
Spin Density Waves ordering in

heavy fermion (narrow band) systems
35
SDW formed by nesting of quasi-particle (HF) bands
1 0.97 0.95
Takeuchi et al., JJAP Ser.11 (1999) 151
36
Further example
1
10
37
Conclusions
Magnetic Instabilities may have different origins
LR-magnetic order may vanish at finite
temperature (not necessarily at T 0)
LR order may be due to localized moments
interaction or to SDW effect
In pressure induced superconductors, TN,C (p)
phase boundary vanishes at finite temperature
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