Thermoelectricity and other effects in Rare Earths compounds with - - PowerPoint PPT Presentation

Thermoelectricity and other effects in Rare Earths compounds with high magnetic disorder.

IICAM and ECOM Workshop on correlated thermoelectric materials.

• Hvar. 26 September 2005

José C. Gómez Sal Universidad de Cantabria. Santander. Spain

Analysis of thermoelectric power for the study of different problems.

Origin of the changes from ferro-to antiferromagnetism in Rare-Earth compounds. The role of the density of states. (RENi1-xCux – REPt1-xCux) Thermoelectricity and Kondo ferromagnets CePt1-xNix. The problem of highly magnetically disordered compounds. May be an open problem for the thermoelecricity CeNi1-xCux

Origin of the changes from ferro-to antiferromagnetism in Rare-Earth compounds. The role of the density of states. (RENi1-xCux – REPt1-xCux)

• The starting point was the wide phenomenology of compounds changing

from Ferro to Antiferro, with the same crystalline structure. In particular 4f

• 3d metals, with only Rare Earth magnetic atoms.
• Pseudobinary RE-3d with RKKY interactions. At that time (75-80) the

change was supposed to be related to the distances between magnetic ions.

• Single ground state magnetism.

Example Orthorhombic. Pnma pseudobinary compounds. Inconmensurate magnetic structures, stable at very low temperatures depending the Kramers or non Kramers character of the RE ion.

• D. Gignoux and J.C. Gómez Sal "Temperature dependence of the incommensurate magnetic structure of

ErNi0.6Cu0.4 compound“. Physics Letters, 50 A, 1, 63-64 (1974). "Magnetic properties and structures of the rare earth compounds RNi1-xCux with FeB type structure"

• J. of Magn. Magn. Mat., 1, 203-213 (1976)

FM AFM

RKKY

Perturbative, discrete calculation

1st order static term 2nd order polarization term ü Spin redistribution ü Positive ü Spin polarization ü Negative baseline

EAFM - EFM EAFM - EFM ∝ n(EF) EAFM - EFM

Free electrons

• A. Hernando, J.M. Rojo, J.C. Gómez Sal & J.M. Novo, J. Appl. Phys. 79, 4815 (1996)

EAFM - EFM

.- A.Hernándo , J.M.Rojo, J.C.Gómez Sal and J.M.Barandiarán. “Density of states and indirect exchange in metallic systems”. Acta Phys.Polonica A, 90, 1227-1234, (1997) A.Hernándo , J.M.Barandiarán, J.M.Rojo and J.C.Gómez Sal. “About the effect of pressure and volume expansion on the transition from antiferromagnetic to ferromagnetic state in some metal alloys: a simplified view”.J.Magn.Magn.Matter, 174, 181-184, (1997)

• A. Señas, J. Rodríguez Fernández, J. C. Gómez Sal , J. Campo.and J.Rodríguez-Carvajal. “From ferromagnetism to inconmensurate magnetic structures: a neutron

diffraction study of the chemical substitution effects in TbPt1-xCux .”Phys.Rev.B 70, 184425, (2004)

• J.Garcia Soldevilla, J.Blanco, J.Rodriguez Fernandez, J.Espeso, J.C.Gomez Sal, M.T.Fernandez Diaz, J.Rodriguez Carvajal and D.Paccard. “ Complex magnetic ordering

in Nd Ni1-x Cux: magnetic structures”. Phys.Rev.B, 70, 224411, (2004)

RKKY

• bjectives

band volume Chemical substitution Pressure üdiscrete tuning üsubstitution

• f

ions increase

• r

decrease the number of conduction electrons ücontinuous tuning üvolume reduction üno introduction of impurities

Origin of magnetism in RE

Periodic table of the elements 28 29 46 47 78 79

Ni Cu Pd Ag Pt Au

58.71 63.54 106.4 107.87 195.09 196.97

[Ar] 3d8 4s2 [Kr] 3d10 [Xe] 4f14 5d9 6s1 [Ar] 3d10 4s1 [Kr] 4d10 5s1 [Xe] 4f14 5d106s1

ΔV, Δe- ΔV

CrB → FeB CrB → FeB CrB → FeB FeB → CsCl FeB → CsCl CsCl

FM FM FM AFM AFM AFM ü Gd3+: huge neutronic absorption ü Tb3+: high magnetic moment ü TbNi1-xCux and TbPt1-xCux

electronic effects

ñ In both series FM-AFM change without or with volume change, respectively ñAFM occurs in TbNi1-xCux for highest cell volumes ñ XPS shows that n(EF) diminishes as Cu increases in TbPt1-xCux

y,b x,a z,c

Tb Pt

z

x 129º-130.2º

• CxFz

z,c x,a y,b

AM (x,y,z)

TbPt1-xCux magnetic structures annealed

TbPt

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

TbCu

D1B ILL & G4.1 LLB

T

“limit compound” 21-39 K AM k||y (x,y,z) ≤30 K –CxFz

x T Q type µB 0 <56 0 -CxFz 7.2 0.2 <47 0

• CxFz 8.2

x T Q type µB 0.4 <36 0, 0.23, 0 AMxyz 9.0 0.6 <37 0.15, 0, 0.22 AMxyz 8.9

TbPt/Ni1-xCux under pressure volume effects .LLB I.Goncharenko

TbPt

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

TbCu TbNi

PROBLEMS: üTexture üPreferred orientations üInhomogeneities üFocalisation üInstrument

z,c x,a +26º

In the -CxFz Ferromagnetic moments rotation towards AFM x-axis

ñ Detailed sample characterisation. ñ Complex analysis due to signal to noise ratio.

ñPnma seems stable up to 65 kbar . Soft changes induced by hydrostatic pressures

ñElectronic rather than volume effects control the sign of the RKKY interaction ñXPS indicates n(EF) as the key parameter

ñPressure favours AFM ñNi-series in spite of V increase, AFM appears with increasing Cu-e- ñPt-series no V changes but AFM also appears with increasing Cu-e-

Thermopower measurements

• Institut de Cienciès de Materials de Barcelona ICMB. J.Fontcuberta (77-300 K) by using a differential method.

RNi1-xCux (R=Gd and Nd) and GdCu1-xPtx.

• btain density of states information from transport properties, and thermopower in particular,

is not an easy task, we can argue that at temperatures well above the magnetic ordering temperature, only the diffusive and phonon contributions of S(T) should be present. Furthermore a linear dependence of S(T) is typically found in those systems in which the diffusive term dominates. In this case, we can write

• S(T)= - (π2kB

2 T / 3e) {dlnl(E)/dE + dlnA(E)/dE}E=EF

l is the mean free path of conduction electrons, A(E) the area in k-space of the energy surface having energy E [proportional to N(E)]

generally for d and f metals, dlnl(E)/dE < dlnA(E)/dE

the slope dS(T)/dT in the linear part of the S(T) plot depends on {N (E) -1. dN(E)/dE}E=EF. Considering a general shape N(E) = Ep, and that the value of dN(E)/dE is not expected to

approximate proportionality between the (dS/dT) slope and N(EF)-1 for the same series compounds.

Experimental results

N(E)/dE has to be negative essential features of the high temperature thermopower can be described on the basis of hole like conduction dS/dT in all the samples studied is positive, GdPt1-xCux , no distinct behaviour can be clearly deduced from the S(T) curves, within the experimental accuracy A general comment should be stressed, FM GdPt0.8Cu0.4 compound shows smaller slopes in the whole temperature range than those of the GdPt0.4Cu0.6 and GdPt0.2Cu0.8 AF compounds. GdNi1-xCux and NdNi1-xCux series linear range (150 - 300 K), inverse slopes of the S(T) curves can be derived

• Compound

Crystalline Magnetic 1/(dS/dT)

• Structure

Character K2 µV-1

• GdAg*

FeB AF 12.8

• GdNi

CrB FM 124.3

• GdNi0.7Cu0.3

FeB FM 59.6

• GdNi0.4Cu0.6

FeB AF 36.8

• NdNi0.6Cu0.4

FeB FM 222.7

• NdNi0.3Cu0.7

FeB FM 154.2

• NdNi0.2Cu0.8

FeB FM 294.1

• NdCu

FeB AF 20.0

• GdNi0.8Co0.2**

CrB FM 93.7

Other systems in which the rule of distance seems to fail: for example GdM (M= Cu, Ag, Au) compounds are AF for Cu and Ag but FM for Au whereas the lattice constant of GdAu is intermediate between the other two.

Only indications are obtained from Thermopower, surely, the temperature range was not the appropriate and in any case is very difficult to obtain information about density of states due to the many effects involved However the complete study (neutron diffraction, XPS) is conclusive about the preponderant role of electronic effects in this problem.

Interest of f-intermetallic compounds with competing interactions JKn(EF) experimentally tuned by

• Applied pressure
• Chemical pressure : Chemical Substitutional systems →

DONIACH PHASE DIAGRAM

• Disorder effects
• Electronic effects

CePt1-xNix RKKY-Kondo competition:

JK n(EF)cr TC→ 0 K

Anomalous behavior: NFL at low T

• CeCu6-xAux - (YU)Pd3 -UCu5-xPdx

and many more…… TK ∝ exp(-1/JkfN(EF)) TRkkY∝JKf

2n(EF)

TC

Jkn(EF) T

FL

MAGNETIC GROUND STATE NON MAGN. GROUND STATE HEAVY FERMION …….. Jkn(EF)cr

Ji Ji+1 Ji JK k s

Long-range RKKY magnetic interaction

HKondo= -JK· s ·Ji

Hybridisation localised 4f–conduction electron

The case of CePt1-xNix

• D. Gignoux, J. C. Gómez Sal, Phys. Rev. B 30, 3967 (1984)
• J. A. Blanco, M. de Podesta, J. I. Espeso, J. C. Gómez Sal, C. Lester, K. A. McEwen, N. Patrikios and J. Rodriguez.

Fernandez, Phys. Rev. B 15126 (1994)

CeNi is intermediate valence, CePt is one of the few Kondo-ferromagnet. Tc = 6K. It has been demonstrated that the Ce3+ state is increasingly screened by Kondo effect with the rise of Ni concentration, x, leading to a gradually decrease of the magnetic moment. The disappearance of the magnetic order

• ccurs at x = 0.95. These features are due

to the increasing importance of the 4f- conduction band hybridization respect to the magnetic RKKY interactions and are interpreted on the ground of the diagram proposed by Doniach .

Thermopower measurements were proposed by J.Sakurai and Y.Isikawa. Toyama University

• Thermoelectric power, S (T), is known to be a quantity very sensitive to details of the

conduction mechanism

• The first motivation of the study was to investigate any special feature of S (T)

related to the Kondo-ferromagnetic character of these samples

• Previous studies of S (T) on other Ce compounds, such as Ce(Pb1-xSnx)3, Ce(Rh1-

xNix)2Si2, Ce(Pd1-xNix)2Si2, were found to have similar drastic changes with the x values of these alloys.

• J. Sakurai, in Encyclopedia of Materials: Science & Technology, Pergamon Press (2001)
• J. Sakurai, H, Kamimura and Y. Komura, J. Magn. Magn. Mater. 76 & 77, 287 (1988)
• E. V. Sampathkumaran, R. Vijayaraghavan, A> Adam, Y. Yamamoto, Y. Yamaguchi and J. Sakurai, Solid State Commun. 71, 71 (1989)
• D. Huo, J. Sakurai, O. Murayama, Y. Kuwai and Y. Isikawa, J. Magn. Magn. Mater. 226-230, 202 (2001)
• The S (T) behavior of these alloying systems was also explained on the basis of the

Doniach’s diagram.

• It is worth to be noticed that the magnetic order in these examples is

antiferromagnetic as in most of the Ce Kondo lattice compounds. Thermoelectric power of CePt1-xNix. J.Phys.Soc Japan,71, 2829,(2002)

Junji Sakurai, Akira Iwasaki, QingFeng Lu and Y. Isikawa Department of Physics, Toyama University, Japan

• J. Rodriguez Fernandez and Jose Carlos Gomez Sal

Facultad de Ciencias, Universidad de Cantabria, Santander, Spain

• The S (T) curves present a continuous evolution

through the studied compositions.

• A common feature is the huge and broad peak at

about 100 K, similarly to many other Kondo compounds having hybridization between the Ce 4f electron and the conduction electrons The thermoelectric power S was measured by measuring differential electric potential DF The typical dimension of the rod sample was of 1*1*4 mm3. The measurement was carried out in a temperature range from 2 K to the room temperature. For the richer Ni compounds x>0.9 we recover the characteristic features of the IV compounds. CeNi (x = 1) and x = 0.95 samples, show only the broad maximum characteristic of IV with strong fluctuations (enhanced Pauli paramagnet). The temperature of the maximum of the S (T) curve corresponds to the characteristic spin fluctuation temperature. For the samples with LRMO and non zero Ce magnetic moment, ( x < 0.95), the Ce 4f state is an ionic state with the energy levels split by the crystalline electric field (CEF). The 4f-conduction band hybridization coexisting with the CEF effect induces a maximum in S (T) curve. The temperature of the maximum corresponds to the total energy separation between the CEF levels. Similar effect as in the magnetic resistivity ρmag (T). The S (T) curves are very reminiscent of rmag (T)..

The initial slopes, α, of the S (T), estimated at T = 0 have the same variation as that of the electronic specific heat, γ, with Ni concentration, x, presenting a broad maximum at around x = 0.85, near to the concentration of disappearance of the ferromagnetic order. The resonance model including an effective molecular field proposed by Bredl et al.(1978) Agreement only quantitative

for x > 0.75 reach near 5 mV/K2 is a high value. very small for the others

Shoulders of the S (T) curves at around T = 10 K, Related to the ferromagnetic order. The same feature in resistivity. For antiferromagnetic compounds of Ce having the Kondo character, the S (T) curves do not show clear indications of

• TN. Then this is a special feature for the Kondo ferromagnets

however we cannot advance the reason why the effect of TC appears clearly on the S (T) curves for the samples of the present study. Appearance of the broad and shallow minima of the S (T) curves around 20 K for the samples with x = 0.50, 0.25 and 0.0.Slight changes of the curvature of S (T) just above the knee, for the samples with x = 0.75, 0.80 and 0.85. The origin could be the same as in the Kondo antiferromagnet, (the existence above TC of short-range Ce 4f electron correlations (in this case ferromagnetic) or could be due to the phonon-drug effect. May be Kondo coherence effects.

The phonon-drug contribution decreases usually for the alloying samples, because the atomic disorder in the alloy tends to decrease the thermal conductivity. We have no thermal conductivity data of the present samples but its electrical resistivity is rather small. Thus, the thermal conductivity is expected to be large enough to not discard the phonon drug effect in our samples.

Fischer’s theory (1989) the superposition of Kondo interaction and the magnetic correlation effect of Ce 4f electrons would lead to the thermoelectric power with a positive sign for a ferromagnet and a negative sign for an antiferromagnet But…. The results are not conclusive.

CeNi1-xCux system. Previous studies

• CONDUCTION ELECTRONS DECREASE IN NUMBER

CeCu

DECREASING CELL VOLUME INCREASING KONDO EFFECT LOCALISED Ce+3 NON LOCALISED

FM AFM CeNi

CeNi1-xCux the situation in 1998, (JGarcia Soldevilla thesis)

TK = 1 K TK = 2 K

Cu Ni Ce

Spin-glass-like x= 0.8 x= 0.7 x= 0.2 x= 0.6 x= 0.5 x= 0.9 x= 0.4 x= 0.3 x= 0.1

• µ strongly reduced due to

the increasing Kondo effect

TK from QENS CeNi0.4Cu0.6

Low T characterisation:

• Specific heat
• ac Susceptibility
• Magnetic neutron diffraction

Spin-glass freezing above TC

ac-dc magnetisation down to 1.8 K

• J. García Soldevilla et al, Phys. Rev. B 61, 6821 (2000)

CeNi1-xCux system. Questions arising

Magnetic Phase Diagram QUESTIONS ARISING

1) Existence of a Quantum Phase Transition in CeNi1-xCux?

Could Non-Fermi-Liquid behavior be expected ~xcr ?

2) What is the origin of such SGL phase above “TC”?

What kind of mechanism leads to a FM state below freezing state? How SGL phase evolves along the series?,

the answer in the Noela Marcano Thesis 2005

U2PdSi3 [D. X. Li, Phys. Rev. B 57 (1998)] URh2Ge2 [S. Süllow, Phys. Rev. B 61 (2000) 8878] CeNi2Sn2 [C. Tien, Phys. Rev. B 65 (2002) 214416]

Different experimental techniques:

• Spin-dynamical processes → Different time window

Microscopic probes → Sensitive to different coherence lengths Neutron: probe of long-range correlations Muon: Sensitive to short-range and other forms of disordered magnetism CeNi1-xCux system. Methodology

Mössbauer

X= 0.7 X= 0.4 X= 0.2 X= 0.6 X= 0.5 X= 0.3

Ferromagnetism

Neutron diffraction down to 50mK D1B, D20 (ILL), E6 (HMI) Neutron response " Collinear FM structure Strong reduce of Ce magnetic moment

CeNi0.4Cu0.6 q= (0,0,0)

b a

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 1 2 3 4 5 6 7 8 0.2 0.4 0.6 0.8 1

Ordered moment (µ

B)

Ordering temperature (K) composition (x) CeNi CeCu CrB FeB

CeNi1-xCux

moment (neutrons) TC AFM FM µSR

CeCu X=1 CeNi X=0

X= 0.8 X= 0.7 X= 0.4 X= 0.2 X= 0.6 X= 0.5 X= 0.3 X= 0.15 X= 0.9 X= 0.1

FIRST COMPOSITIONAL REGIME

Exchange interactions: AFM-FM evolution RNi1-xCux

(AFM) (FM)

SECOND COMPOSITIONAL REGIME Kondo interaction: reducing Ce magnetic moment CeNiyPt1-y

Smooth variation about TN : SRO Complex ordered spin structures Macroscopic characterisation. Specific heat N. Marcano et al PRB 71, 134401, 2005 the pics are at the same temperature as the AC susceptibility

Cmag IN THE LOW TEMPERATURE REGIME

Cmag ∝ T3/2

T<Tcrít

Ferromagnetic-like spin waves developing although the overall magnetic structure is not ferromagnetic below Tfreezing Similar behaviour in amorphous alloys:

Gd33Al67 [Coey et al, Solid State Commun 24 (1997)] Er50Ni50 [Hattori et al, J. Phys.: Condens. Matter 7 (1995)]

CeNi0.8Cu0.2: Divergence in the CP/T vs T plot reasonably well reproduced by NFL models

Magnetic fluctuations close to the Quantum Phase Transition Cmag/T ∝a log (T/T0)

• A. J. Millis, Phys. Rev. B 48 (1993) 7183

Griffiths Phases : Cmag/T ∝T-1+λ

• A. H. Castro Neto, Phys. Rev. Lett. 81 (1998) 3531

Th1-xUxPd2Al3 (λ = 0.6) UCu5-xPdx (λ = 0.8) AC SUSCEPTIBILITY

Presence of a transition at very low temperatures

AC-DC SUSCEPTIBILITY FOR X<0.2

Magnetic moments not fully exhausted Stability of a long-range ordered state?

Macroscopic characterisation. Specific heat

QCP is questionable in this system

CeCu X=1 CeNi X=0

x= 0.8 x= 0.7 x= 0.2 x= 0.6 x= 0.5 x= 0.15 x= 0.9 x= 0.4 x= 0.3 x= 0.1

Long Range FM

• rder

T<<Tfreezing Short Range FM correlations T<Tfreezing

ξ (CeNi0.4Cu0.6) > ξ (CeNi0.8Cu0.2)

Cluster glass

No additional anomalies at T<Tfreezing….

Mechanism that leads from cluster-glass state to LRO (mK)? µSR SPECTROSCOPY

− Mainly sensitive to short-range correlations − Spin dynamical frequencies : bridges bulk- neutron diffraction − µSR signal proportional to the volume fractions in a magnetically inhomogeneous system Microscopic characterisation. Neutron Scattering

µSR on CeNi1-xCux

Intermediate state connecting Paramagnetic- LRO regime

CeNi0.8Cu0.2

Intermediate state. Non-ordered fraction has increased Non-ordered fraction

• nly

(Paramagnetism) Pure LRO spectrum Strong local spin disorder Λtrans>γB B~7mT è µ=0.1µB

• rdered + non-ordered

fractions (intermediate state)

CeCu X=1 CeNi X=0

x= 0.8 x= 0.7 x= 0.2 x= 0.6 x= 0.5 x= 0.15 x= 0.9 x= 0.4 x= 0.3 x= 0.1

Intermediate (inhomogeneous) state: MAGNETIC HISTORY EFFECT Spectra differ whether T is reached by ZFC or by FC FC → sample cooled from T>10K in 50 mT Longitudinal Field to measurement T. Measurement in Zero Field Microscopic characterisation. µSR spectroscopy N.Marcano et al Physica Scripta 68,298-318,(2004)

Temperature Tfreezing (AC, Cp)

INTERMEDIATE STATE Short range interactions Magnetic clusters formation Dynamic clusters PARAMAGNETIC STATE Thermal fluctuations

• vercome

the exchange interactions Free spins

T* (µSR)

LONG RANGE ORDER STATE Magnetic clusters percolate LRO state FM structures

General discussion: Phenomenological scenario CeNi1-xCux

CeCu X=1 CeNi X=0

x= 0.8 x= 0.7 x= 0.2 x= 0.6 x= 0.5 x= 0.15 x= 0.9 x= 0.4 x= 0.3 x= 0.1

D16 0.03Å-1<Q<0.65Å-1 T= 1.86 K < Tfreezing

ξ= 17(3)Å

Microscopic characterisation. Neutron Scattering

CeCu X=1 CeNi X=0

x= 0.8 x= 0.7 x= 0.2 x= 0.6 x= 0.5 x= 0.15 x= 0.9 x= 0.4 x= 0.3 x= 0.1

D16 0.03Å-1 < Q < 0.65Å-1 T= 1.57 K < Tfreezing

ξ= 27(1)Å

Short Range Ferromagnetic correlations FERROMAGNETIC CLUSTERS T < Tfreezing Microscopic characterisation. Neutron Scattering

Hysteresis loops at very low T in FM compounds: CeNi0.6Cu0.4, CeNi0.5Cu0.5,

CRTBT (Grenoble) :

• N. Marcano , C. Paulsen,
• E. Lhotel, Ch. Sekine
• Role of T
• Cycling

effects

• Field variation

Sensitive to various experimental parameters Magnetization steps found in manganites, molecular magnets, UGe2, etc.. Our proposal is

Avalanches , or giant Barkhausen effect, is a proof of the clustering state at low temperatures.

Theory and modelling by B.Coqblin and R.Iglesias in progress

• Inhomogeneities

– present in mixed or substitutional compounds – Intrinsic: they cannot be avoided

• Infer particular phenomenology:

Magnetic clusters Cooperative interactions Randomness

• Percolation…….

Is this phenomenology more general than expected? Thermoelectric measurements could help in this analysis?

High TC Superconductors

AFM (insulator)-Superconducting: clustered regime

• La2-xSrxCuO4:

Scanning SQUID microscopy Iguchi et al, Nature 412, (2001) 420 Burgy et al,

• Phys. Rev. Lett. 87,

(2001) 277202

MANGANITES

Experimental evidences

Percolative phase separation underlies CMR in mixed-valent manganites CMR explained by percolative transport through FM domains

• M. Uehara et al, Nature 399 (1998) 560.
• La1-xCaxMnO3 (x∼0.3)

CMR viewed as a percolation of metallic FM domains. T<Tc Phase separation Inhomogeneous structure of metallic and insulating areas coexists Strongly field dependent in size and structure

• M. Fäth et al,

Science 285 (1999) 1540.

People involved in the experiments

SAMPLES

Arc melting

Thermal treatments Crystallographic study X-Ray diffraction SEM (Luciano Sánchez, UC) 4 circle X-Ray diffraction Savoie University

• D. Paccard

Neutron Diffraction G.4.1, G.4.2 (LLB)

Microscopic techniques

µSR SPECTROSCOPY (0.05 K <T< 1.1 K)

LTF (PSI)

• C. Baines

(1.7 K <T< 300 K)

GPS (PSI) A.Amato

• G. M. Kalvius
• D. R. Noakes
• R. Wäppling

NEUTRON DIFFRACTION

Dilution regime: E6 (HMI)

• J. Hernández Velasco

D20 (ILL)

• C. Ling

SANS D11

• B. Farago

D16

• J. M. de Teresa

SPECIFIC HEAT (0.2 K <T< 6 K)

Quasiadiabatic calorimeter

• Un. Zaragoza-ICMA
• F. Bartolomé
• J. Herrero

(0.2 K <T< 6 K)

QD microcalorimeter

• Un. Cantabria

Macroscopic techniques

AC-DC MAGNETISATION

(0.07 <T< 12 K)

SQUID 3He-4He CRTBT(CNRS)

• C. Paulsen
• E. Lhotel, Ch.Sekine

(1.8 K <T< 300 K)

PPMS Magnetometer

• Un. Cantabria

MAGNETORRESISTANCE (0.4 K <T< 2 K)

• A. Otop, S. Süllow

Analogous to observed in other systems:

Steplike metamagnetic transitions on Pr0.5Ca0.5Mn0.95Co0.05O3

• R. Mahendiran et al, Phys. Rev. Letters, 89

(2002) 286602.

UGe2 S.Saxena Et al Nature (2002). Nisioka et al PRL (2002)

Pr0.5Ca0.5Mn0.95Ga0.05O3 Sensitive to experimental parameters

• V. Hardy et al, J. Magn. Magn. Mat., 264

(2003) 183.

Cmag IN THE LOW TEMPERATURE REGIME

X= 0.5, 0.4 λ-Type anomaly at Tfreezing X= 0.9 AFM TN X= 0.6 Broad hump at Tf

Cmag : marked anomalies at Tfreezing by ac-Susceptibility Canonical Spin Glass: Shape of the anomalies differs from expected around Tf

Macroscopic characterisation. Specific heat.

TbPt/Ni1-xCux under pressure volume effects

TbPt

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

TbCu TbNi

experimental data theoretical data

z,c x,a +26º

moments rotation towards AFM x-axis

• CxFz

Disorder-driven NFL behavior Kondo Disorder Model

Bernal et al, PRL 75, 2023 (1995) Disordered system at a QCP Miranda et al, PRL 86, 264 (2001)

• N. Bernhoeft, J. Phys: Cond. Matt 13

(2001)

Griffith’s phase scenario:

RKKY-Kondo competition in a disordered material: Magnetic clusters and Griffiths’ singularities Castro Neto et al, PRL 81, 3531(1998)

URh2Ge2 :

Annealing dependence of electronic and magnetic properties Spin-Glass state/ AFM Quasi-insulating/metallic behavior

• S. Süllow et al, PRB 61(2000) 8878
• S. Süllow et al, J.M.M.M 226-230 (2001) 35
• 39.

NFL and SG behavior for x= 1, 1.5 compounds

• R. Vollmer et al, PRB,Vol 61, (2000) 1218

NFL and disorder in UCu5-xPdx UPd2-xSn :

Unusual transport properties for 0≤x≤0.15 relevance of crystallographic disorder Maksimov et al, PRB 67(2003) 104405

• LRO no detected for x≤0.2 by neutron diffraction
• Specific heat suggest NFL behavior for x=0.2

CeNi0.8Cu0.2

C/T∝ a log(T/T0) C/T∝ T-1+λ