Magnetic, Transport and Thermal Properties of LaMagnetic, Transport and Thermal Properties of La0.670.67PbPb0.330.33(Mn(Mn1-x1-xCoCoxx)O)Oyy

M. MIHALIK, V. KAVEČANSKÝ, S. MAŤAŠ, M. ZENTKOVÁ Institute of Experimental Physics, SAS, Košice, Slovak Republic

ANDJ. AMMER, K. KELLNER, G. GRITZNER

Institute for Chemical Technology of Inorganic Materials, Johanes Kepler University, Linz

Goal: Goal: effect of Co doping into Mn siteseffect of Co doping into Mn sites0.01 0.01 x x 0.150.15

Linz Linz synthesissynthesischaracterizationcharacterizationXRD measurementsXRD measurements

KošiceKošiceXRD interpretationXRD interpretationmagnetizationmagnetization, , AC susceptibilityAC susceptibility (MPMS) (MPMS)resistanceresistance, MR and , MR and heat capacityheat capacity

project: No SK-05/06-KE-005project: No SK-05/06-KE-005

Appl. Phys. A (2007) Appl. Phys. A (2007) DOI: 10.1007/s00339-007-4284-2Acta Physica Polonica A (2008)

IntroductionIntroduction

Jahn-Teller effectJahn-Teller effect

The re-discovery of colossal magnetoresistance (CMR) in hole doped perovskites in the early 1990s gave rise to a new investigation.

The ferromagnetic and metallic properties of this type of compound were explained by means of the double exchange (DE) mechanism that involves Mn3+ – O– Mn4+ bonds.

The substitution of the Mn ions by other transition metal ions it gives rise also to changes in the Mn3+ : Mn4+ ratio, with important modifications in the magnetic and transport properties.

This simple concept cannot explain all the phenomena, about the metal-insulator (M-I) transision and an additional effects such as lattice distortions, orbital degree of freedom or electron correlation should be consider.

Double exchangeDouble exchange

Crystal structureCrystal structure

R -3 c a = 5.5168(2) c = 13.3891(4)

(La0.67Pb0.33)(Mn0.9Co0.1)O3

atóm x y z occ

La 0.00000 0.00000 0.25000 0.1117

Pb 0.00000 0.00000 0.25000 0.0550

Mn 0.00000 0.00000 0.00000 0.1500

Co 0.00000 0.00000 0.00000 0.0167

O 0.45039 0.00000 0.25000 0.5000

Crystal structure - summaryCrystal structure - summary

• The averaged crystal structure revealed no deformations of the octahedral The averaged crystal structure revealed no deformations of the octahedral coordination of Mn/Co – O. coordination of Mn/Co – O.

• Average bond valence sum for the Mn/Co site decreases and the average bond Average bond valence sum for the Mn/Co site decreases and the average bond valence sum for the La/Pb site increases with increasing Co content. Such valence sum for the La/Pb site increases with increasing Co content. Such behavior may be accounted for by stresses and strain within the crystal lattice. behavior may be accounted for by stresses and strain within the crystal lattice.

• We believe thatWe believe that induced strain by the substitution is compensated by rotation of induced strain by the substitution is compensated by rotation of the Mn/Co - O6 octahedrons. the Mn/Co - O6 octahedrons.

Magnetic propertiesMagnetic properties

0 50 100 150 200 250 300 350

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

oH = 5 mT

x = 0.01 x = 0.06 x = 0.10 x = 0.15

La0.67

Pb0.33

(Mn1-x

Cox)O

3

( B

/f.u.

)

T (K)

200 220 240 260 280 300 320 340 360 380

0.0

5.0x105

1.0x106

1.5x106

2.0x106

2.5x106

TJT

La0.67

Pb0.33

(Mn0.85

Co0.15

)O3

= 256 K

eff = 5.71

B

exp. data Curie Weiss law (CW) CW fit below T

JT

1/

(mo

l/m3 )

T (K)

190 200 210 220 230 2400.0002

0.0004

0.0006

0.0008

0.0010

0.0012

0.0014

0.000

0.020

0.040

0.060

0.080

f = 1.111 Hz f = 111.1 Hz

La0.67

Pb0.33

(Mn0.85

Co0.15

)O3

'' (

em

u/g

)

T (K)

f = 1.111 Hz f = 111.1 Hz

0H = 0.25 mT

' (e

mu

/g)

x 0.01 0.03 0.06 0.10 0.15

TC [K] (µ0H < 0.1 mT) 335 322 291 256 227

Θ [K] (µ0H = 5.0 mT) 338* 325* 300 281 256

µeff [µB] (µ0H = 5.0 mT) 6.33* 6.40* 6.45 6.13 5.71

TJT [K] (µ0H = 5.0 mT) - * - * 350 345 330

µs [µB] (T = 1.8 K) 3.73 3.63 3.64 3.55 3.55

µrem [µB] (T = 1.8 K) 0.27 0.43 1.24 1.34 1.77

µ0Hc [mT] (T = 1.8 K) 4 16 37 56 105

-1.0 -0.5 0.0 0.5 1.0

-3

-2

-1

0

1

2

3

T = 1.8 K

La0.67

Pb0.33

(Mn0.85

Co0.15

)O3

( B

/f.u.

)

0H (T)

0 1 2 3 4 5-4

-3

-2

-1

0

1

2

3

4

x = 0.01 x = 0.03 x = 0.06 x = 0.10 x = 0.15

T = 1.8 K

La0.67

Pb0.33

(Mn1-x

Cox)O

3

( B

/f.u.

)

0H (T)

Magnetic propertiesMagnetic properties

Magnetic properties - summaryMagnetic properties - summary

• TTJT JT decreasesdecreases with doping - the Jahn-Teller effect is reduced with Co-doping.with doping - the Jahn-Teller effect is reduced with Co-doping.

• The ferromagnetic character of the un-doped compound still remains after Co-The ferromagnetic character of the un-doped compound still remains after Co-doping for whole concentration range. doping for whole concentration range.

• The Curie temperature The Curie temperature TTCC, the paramagnetic Curie temperature , the paramagnetic Curie temperature ΘΘ, the effective , the effective magnetic moment magnetic moment µµeffeff and the saturated magnetization and the saturated magnetization µµss decrease with increasing decrease with increasing Co-doping. Co-doping.

• The decrease in the magnetic characteristics indicates antiferromagnetic coupling The decrease in the magnetic characteristics indicates antiferromagnetic coupling between Mn and Co ions and/or a dilution effect by Cobetween Mn and Co ions and/or a dilution effect by Co3+3+ ions, which are mostly in ions, which are mostly in the low spin state with the low spin state with SS = 0. = 0.

• The CoThe Co3+3+ ion ion reduce the population of hoping electrons and available hoping sites; reduce the population of hoping electrons and available hoping sites; DE is then progressively suppressed, weakening the ferromagnetism. DE is then progressively suppressed, weakening the ferromagnetism.

• Remanent magnetization Remanent magnetization µµremrem and the coercive field and the coercive field HHcc increase with Co-doping, increase with Co-doping, which can be related to highly anisotropic nature of Co, or to defects introduced by which can be related to highly anisotropic nature of Co, or to defects introduced by doping.doping.

0 50 100 150 200 250 300 350-0.05

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40 La0.67

Pb0.33

(Mn1-x

Cox)O

3

x = 0.01 x = 0.03 x = 0.06 x = 0.10 x = 0.15

MR

T (K)

0 100 200 300

0.01

0.1

0H = 0 T

x = 0.10 x = 0.06 x = 0.01 x = 0.03

La0.67

Pb0.33

(Mn1-x

Cox)O

3

0H = 1 T

x = 0.10 x = 0.06 x = 0.01 x = 0.03

(.

cm)

T (K)

0 70 140 210 280 350-10

0

10

20

30

40

50

60

70

80

90

180 200 220 240 260

0.6

0.8

1.0

1.2

1.4

(.

cm)

T (K)

La0.67

Pb0.33

(Mn0.85

Co0.15

)O3

B = 0 T B = 1 T

(.

cm)

T (K)

x 0.01 0.03 0.06 0.10 0.15

TC [K] (µ0H = 0.0 T) 337 322 288 257 228

TC [K] (µ0H = 1.0 T) 348 334 294 265 240

T * [K] (µ0H = 0.0 T) 28 25 32 46 48

T* [K] (µ0H = 1.0 T) 16 17 26 43 50

Tp [K] (µ0H = 0.0 T) 270 266 244 183 106

Tp [K] (µ0H = 1.0 T) 276 275 249 188 109

Resistance and magnetoresistance propertiesResistance and magnetoresistance properties

HHH

MR

0

B.C. Zhao, et al., Phys. Rev. B 72 132401 (2005)

0 50 100 150 200 250 300 350

0.00

0.05

0.10

0.15

0.20

from top

0H = 9.0 T

0H = 5.0 T

0H = 3.0 T

0H = 1.0 T

La0.67

Pb0.33

(Mn0.9

Co0.1

)O3

0 - H

(.

cm)

0H = 0.0 T

0H = 1.0 T

0H = 3.0 T

0H = 5.0 T

0H = 9.0 T

(.

cm)

T (K)-2 -1 0 1 2

6

7

8

9

40

50

60

La0.67

Pb0.33

(Mn0.85

Co0.15

)O3

T = 2.5 K T = 45 K

(.

cm)

0H (B)

0 50 100 150 200 250 300 350

0.000

0.008

0.016

0.024

0.032

0.040

0.048

0.056

0H = 9.0 T

0H = 5.0 T

0H = 3.0 T

0H = 1.0 T

La0.67

Pb0.33

(Mn0.99

Co0.01

)O3

0 - H

(.

cm)

0H = 0.0 T

0H = 1.0 T

0H = 3.0 T

0H = 5.0 T

0H = 9.0 T

(.

cm)

T (K)0 100 200 300 400

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

La0.67

Pb0.33

(Mn0.99

Co0.01

)O3

0H = 9.0 T

0H = 5.0 T

0H = 3.0 T

0H = 1.0 T

MR

T (K)

Resistance and magnetoresistance propertiesResistance and magnetoresistance properties

• The ferromagnetic transition is accompanied by an anomaly in electrical resistance The ferromagnetic transition is accompanied by an anomaly in electrical resistance for all compounds.for all compounds.

• The metal - insulator transitions do not coincide with the relevant Curie The metal - insulator transitions do not coincide with the relevant Curie temperatures.temperatures.

• The “extrinsic” part of the resistivity is responsible for broad maxima in the The “extrinsic” part of the resistivity is responsible for broad maxima in the ρρ((TT), ), which are due to I-M transitions.which are due to I-M transitions.

• DE suppression induced weakening the metallic behavior of the samples.DE suppression induced weakening the metallic behavior of the samples.

• The intermediate state below the re-entrant transition is characterized not only by the The intermediate state below the re-entrant transition is characterized not only by the tunneling intergrain mechanism but also the observed enhancement of resistivity arises tunneling intergrain mechanism but also the observed enhancement of resistivity arises from the transition of orbibal order-disorder states (field dependence of from the transition of orbibal order-disorder states (field dependence of TT*) and/or from *) and/or from an effective Coulomb barrier of electrostatic origin.an effective Coulomb barrier of electrostatic origin.

• The high-temperature I-M transition at The high-temperature I-M transition at TTp, observed for all compounds decreases with p, observed for all compounds decreases with Co-doping and the re-entrant temperature Co-doping and the re-entrant temperature TT*, observed at low temperatures, increases *, observed at low temperatures, increases with Co-doping.with Co-doping.

• The applied magnetic field smears out the anomaly at The applied magnetic field smears out the anomaly at TTCC, increases both , increases both TTpp and and TTCC but on but on the other hand decreases the other hand decreases TT*.*.

• All studied samples show large magnetoresistance.All studied samples show large magnetoresistance.

Resistance and magnetoresistance - summaryResistance and magnetoresistance - summary