Hall effect and conductivity in the single crystals of La-Sr and La-Ba manganites

N.G.Bebenin1), R.I.Zainullina1), N.S.Chusheva1), V.V.Ustinov1), Ya.M.Mukovskii2),

1)Institute of Metal Physics, UD RAS, Ekaterinburg, Russia2)Moscow State Steel & Alloys Institute, Moscow, Russia

1. Introduction

2. Resistivity and Hall effect far below Curie temperature

2.1. The x<xc crystals: La0.85Sr0.15MnO3, La0.85Ba0.15MnO3, and La0.80Ba0.20MnO3

2.2. The x>xc crystals: La0.80Sr0.20MnO3, La0.75Sr0.25MnO3, and La0.72Ba0.28MnO3

3. Temperature-induced metal-semiconductor transition

4. Near TC and in the paramagnetic state

5. Conclusion

Resistivity of La1-xSrxMnO3 single crystals(Urushibara et al., PRB 1995)

Resistivity of La1-xSrxMnO3 single crystals(Anane et al., J. Phys.:Condens. Matter 1995)

Resistivity of La1-xSrxMnO3 and La1-xBaxMnO3 single crystals(Bebenin et al., PRB 2004, JETP 2000, J. Phys.: Condens. Matter 2005, JMMM 2006)

Blue line: inverse minimum metallic conductivity, σmin-1, according to Salamon and

Jaime, RMP 2001

0 50 100 150 200 250 300 350 400 450

1E-4

1E-3

0,01

0,1

1

10

100

1000

Re

sist

ivity

(

cm)

Temperature (K)

Sr0.15

Ba0.15

Ba0.20

Ba0.28Sr0.25

Sr0.20

Magnetoresistance Δ/=[(H)-(0)]/(0) for La-Sr single crystals (H=10 kOe)

50 100 150 200 250 300 350 400 450

0,0

0,1

0,2

0,3

0,4

Temperature (K)

Sr0.15 Sr0.20

Sr0.25

Magnetoresistance Δ/ for La-Ba single crystals (H=10 kOe)

50 100 150 200 250 300 350 400 450

0,0

0,1

0,2

0,3

0,4

0,5

Ba0.28

Ba0.20

-

Temperature (K)

Ba0.15

Electronic specific heat coefficient γ for La1-xSrxMnO3 (T.Okuda et al. PRL 1998)

Resistivity and thermopower data suggest that in La0.85Sr0.15MnO3 (TC=232 K) and La0.85Ba0.15MnO3 (TC =214 K) variable range hopping (VRH) dominates

below 100 K.

-0,15 -0,10 -0,05 0,00 0,05 0,10 0,15

0,6

0,8

1,0

1,2

1,4

Den

sity

of s

tate

s (a

rbit.

uni

ts)

Energy (eV)

0=k

BT1/4

0T3/4

0(T=100 K) = 0.117 eV

La0.85

Sr0.15

MnO3

-0,15 -0,10 -0,05 0,00 0,05 0,10 0,15

0

1

2

3

4

5

Den

sity

of s

tate

s (a

rbit.

uni

ts)

Energy (eV)

0=T1/2

1T1/2

0(T=100 K)=0.115 eV

La0.85

Ba0.15

MnO3

Mott’s model Shklovskii-Efros model

Hall resistivity vs magnetic field for La0.72Ba0.28MnO3 (TC=310 K)

Hall=RoH+RsM

0 2 4 6 8 10 12 14 16

-5,0x10-7

-4,0x10-7

-3,0x10-7

-2,0x10-7

-1,0x10-7

0,0

250 K

H

all (

cm)

Magnetic field (kOe)

90 K

130 K

170 K

210 K

Hall mobility in the single crystals with x<xc.xc=0.17 for La1-xSrxMnO3,

xc≈0.22 for La1-xBaxMnO3

100 150 200 250-0,15

-0,10

-0,05

0,00

0,05

0,10

H

all

mo

bili

ty (

cm2 V

-1 s

-1)

Temperature (K)

Ba0.20

Sr0.15

Ba0.15

Low temperature (T< 200K) resistivity in the x>xc crystals obeys T2-law

0 2 4 6 80

1

2

3

Sr0.25

Sr0.20

Re

sist

ivity

(m

cm)

T2 (104 K2)

Ba0.28

(T)=(0)+AT2

Hall mobility in the x>xc La-Sr and La-Ba single crystals

50 100 150 200 250 300 350

-0,5

0,0

0,5

1,0

1,5

2,0

2,5

3,0

Ha

ll m

ob

ility

(cm

2 V -

1 s-1)

Temperature (K)

Ba0.28

Sr0.20

Sr0.25

Resistivity and Hall mobility in La2/3(Ca,Pb)1/3MnO3 single crystal (TC≈290 K) calculated on the base of

data of Chun et al., PRB 1999.

220 230 240 250 260 270 2800,0

0,5

1,0

0,0

0,2

0,4

0,6

0,8

1,0

Re

sist

ivity

(m

cm)

Temperature (K)

La2/3

(Ca,Pb)1/3

MnO3

Ha

ll m

ob

ility

(cm

2 V -

1 s-1)

Anomalous Hall coefficient in La1-xSrxMnO3 single crystals (Bebenin et al., PRB 2004)

0,0 0,2 0,4 0,6 0,8

-20

-15

-10

-5

0

0 100 200 300 400

-20

-10

0

x=0.15

(a)

(b)

x=0.20x=0.25

x=0.25x=0.20x=0.15

RS

(10

-9

cm

G-1)

Temperature (K)

0 10

-6

-3

0

(m cm)

RS

Rs

m2

Hall effect in La2/3(Ca,Pb)1/3MnO3 (Chun et al., PRB 1999)

Resistivity of La-Sr single crystals near Curie temperature

0,0 0,2 0,4 0,6 0,8

-8

-6

-4

-2

Sr0.25 Sr0.20

Sr0.15

ln(

H=

10

kO

e)

m2=(M/Ms)2

Resistivity of La-Ba crystals near Curie temperature (H=10 kOe)

=oexp[(Eo-E1m2)/kBT)

0,0 0,2 0,4 0,6 0,8 1,0-8

-6

-4

-2

0

2

4

ln

m2

Ba0.15

Ba0.20

Ba0.28

Magnetoresistance of La0.72Ba0.28MnO3 (TC=310 K) as a function of m2

0.00 0.05 0.10 0.15 0.20 0.25 0.300.0

0.1

0.2

0.3

0.4

m2

300 K 306 K 313 K 320 K 326 K

Critical behavior of E1(T) in La0.72Ba0.28MnO3

300 310 320 330 340

10

15

20

dE

1/d(k

BT

)

Temperature (K)

Local activation energy εa=d(ln)/d(T-1) for La0.85Ba0.15MnO3 single crystals

100 200 300 400

-0,1

0,0

0,1

0,2

Lo

cal a

ctiv

atio

n e

ne

rgy

(e

V)

Temperature (K)

Temperature dependence of the metallic phase volume in some lightly doped manganites derived from optical measurements

(Mostovshchikova et al., PRB 2004)

Local activation energy εa=dln/d(T-1) in La1-xSrxMnO3

1,2 1,5 1,8

-2000

0

2000

a /k B

(K

)

=T/TC

Sr25

Sr20

Sr15

Conclusion

1. Unlike La1-xSrxMnO3 family, in the x>xc La1-xBaxMnO3 single crystals electrons – not holes - are majority carriers. Thus the band structure depends on not only doping level but also on type of divalent ion.

2. The temperature-induced metal-semiconductor transition, if any, occurs well below TC.

3. Near Curie temperature, where CMR effect is observed, all the crystals are in a semiconductor state. Above TC, the crystals are likely to be in the semiconductor state, too. The sign of d/dT is not a sufficient indication of metallic state.

4. The conductivity mechanisms in the manganites with different doping is different. A general formal reason for the CMR effect in the La-Sr and La-Ba single crystals consists in the change of activation energy under application of a magnetic field.