Thermodynamic and Electron Diffraction Signatures of Charge and Spin Ordering in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi>La</mml:mi></mml:mrow><mml:mrow><mml:mn>1</mml:mn><mml:mo>−</mml:mo><mml:mi mathvariant="italic">x</mml:mi></mml:mrow></mml:msub></mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi>Ca</mml:mi></mml:mrow><mml:mrow><mml:mi mathvariant="italic">x</mml:mi></mml:mrow></mml:msub></mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi

Ramirez, A. P.; Schiffer, P.; Cheong, Sang‐Wook; Chen, C. H.; Bao, Wan-Su; Palstra, Thomas; Gammel, P. L.; Bishop, David J.; Zegarski, Bernard R.

doi:10.1103/physrevlett.76.3188

Cited by 446 publications

(249 citation statements)

References 18 publications

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“…The constant term S 0 has a very simple, unambiguous interpretation: in the high-temperature limit, when effects of interaction can be neglected, it measures the entropy carried by the mobile particles. 11 This quantity should know about the configurational entropy, thereby showing a strong x dependence, and the spin entropy. However, we find experimentally that S 0 is almost x independent.…”

Section: Sϭϫ Smentioning

confidence: 99%

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Transport mechanisms in dopedLaMnO3:Evidence for polaron formation

Palstra

Ramirez²,

Cheong³

et al. 1997

Phys. Rev. B

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172

103

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We report electrical transport experiments on the colossal magnetoresistance compound (La,Ca͒MnO 3 over a wide range of composition and temperature. Comparison of thermopower and electrical resistivity measurements above the metal-insulator transition indicate a transport mechanism not dominated by spin disorder, but by small polaron formation. Additionally, we find that in the high-temperature limit the thermopower corresponds to backflow of spin entropy, expected from motion of positively charged particles in a rigid Sϭ2 system, showing a remarkable independence of Sϭ3/2 particle density. ͓S0163-1829͑97͒09334-X͔The recent observation of large magnetoresistance effects in thin films of doped LaMnO 3 has renewed the interest in the metal-insulator transition in these materials. [1][2][3] Since the metal-insulator transition temperature, T MI , can be tuned to above room temperature, this opens possibilities to use this material not only for recording media but also for other types of magnetic switching applications. However, the emerging notion that magnetoresistance due to a metal-insulator transition decreases with increasing T MI , necessitates a better understanding of the underlying basic transport mechanism to exploit the magnetoresistive properties of these materials fully. The microscopic nature of the transport mechanism is condensed into the description of double exchange, the simultaneous electron transfer of an electron on a Mn atom to an O atom of the surrounding oxygen octahedron, and another electron from this O atom to a neighboring Mn atom. 4 This indirect exchange mechanism establishes, because of spin conservation in the exchange, a direct relation of the metallic state with the ferromagnetic coupling between the Mn spins. However, there is remarkably little known about the transport mechanism in the insulating state. Whereas spin disorder can contribute to the variations in the resistivity near T c , only more recently the role of electron-phonon interactions on the localization has been put in a clearer perspective. [5][6][7] This theoretical work was based on research on magnetic semiconductors like EuO, and only recently applied to doped LaMnO 3 . Still, it is not known if the metal insulator transition in doped LaMnO 3 is driven by changes in the carrier density or the mobility.In order to gain insight into the nature of the transport mechanism, we have performed thermopower measurements on doped LaMnO 3 over a wide range of concentrations and temperatures in addition to the basic characterization by electrical resistivity and magnetic measurements. Thermopower is in contrast to electrical resistivity relatively insensitive to effects of grain boundaries and disorder. We will show that for this material, thermopower provides unique insight into the transport mechanism. First, we show that the change of sign in the thermopower is not related to competition between electron and hole conduction, but accidental cancellation of the entropic term and the energy transport term of the thermopower...

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Section: Sϭϫ Smentioning

confidence: 99%

“…It was shown that for these concentrations a charge ordered ground state forms, which is insulating, exhibiting antiferromagnetic ordering at lower temperature. 11 We show the temperature dependence of the thermopower S(T) of (La,Ca͒MnO 3 in Fig. 2.…”

mentioning

confidence: 99%

Transport mechanisms in dopedLaMnO3:Evidence for polaron formation

Palstra

Ramirez²,

Cheong³

et al. 1997

Phys. Rev. B

Self Cite

172

103

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“…The interest in the mixed perovskites 1,2 La 1−x Ca xMnO 3 has been renewed 3,4,5,6,7,8,9,10,11,12,13,14,15,16 in connection with the discovery of colossal magnetoresistance for x ∼ 0.33. 17 For the high doping range with x > 0.5, the Mn 3+ e g electrons become localized at low temperatures with a concomitant anisotropic bond reorganization in the oxygen environment of the manganeses.…”

Section: Introductionmentioning

confidence: 99%

Crystal and magnetic structure of theLa1−xCaxMnO
Pissas
¹
,
Kallias
²
,
Hofmann³
et al. 2002
Phys. Rev. B
56
1
22
1
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Crystal and magnetic structure of the La 1−x Ca x MnO 3 compound (x = 0.8, 0.85). We studied the crystal and magnetic structure of the La1−xCaxMnO3 compound for x = 0.8 and x = 0.85. At T = 300 K both samples are paramagnetic with crystallographic symmetry P nma. At low temperatures they undergo a monoclinic distortion from orthorhombic P nma-type structure with ap √ 2 × 2ap × ap √ 2 to a monoclinic structure with (ap √ 2 × 2ap × ap √ 2, β = 90 + ε ∼ 91.4 o ) and P 21/m space group below TN . The onset of the structural transformation coincides with the development of the C-type long range antiferromagnetic order with propagation vector k = ( 1 2 , 0, 1 2 ). The monoclinic unit cell allowed us to determine the direction of the Mn magnetic moment with respect to the crystallographic axes: it is perpendicular to the propagation vector, m ⊥ k = ( 1 2 , 0, 1 2 ). The amplitude of the ordered magnetic moment at T = 1.6 K is found to be 2.53(2) and 2.47(2)µB for x = 0.8 and 0.85, respectively.

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“…Starting with Ba-and Ca-doped LaMnO 3 , initial measurements at higher temperatures identified specific-heat anomalies associated with phase transitions [1,2], while low-temperature data [2,3,4] showed a linear term associated with an electronic contribution, and a cubic phonon term. Subsequent studies were performed on a variety of samples, including cation-deficient LaMnO 3+δ [5], Nd- [6] and Pr- [7,8,9,10] based compounds, or layered manganites [11].…”

mentioning

confidence: 99%

Disorder effects at low temperatures in La0.7−xYxCa0.3MnO3 manganites

Gusmao¹,

Ghivelder²,

Freitas³

et al. 2003

Solid State Communications

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With the aim of probing the effect of magnetic disorder in the low-temperature excitations of manganites, specific-heat measurements were performed in zero field, and in magnetic fields up to 9 T in polycrystalline samples of La 0.7−x Y x Ca 0.3 MnO 3 , with Y concentrations x = 0, 0.10, and 0.15. Yttrium doping yielded the appearance of a cluster-glass state, giving rise to unusual low-temperature behavior of the specific-heat. The main feature observed in the results is a strong enhancement of the specific-heat linear term, which is interpreted as a direct consequence of magnetic disorder. The analysis was further corroborated by resistivity measurements in the same compounds.

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Thermodynamic and Electron Diffraction Signatures of Charge and Spin Ordering inLa1−xCax

Cited by 446 publications

References 18 publications

Transport mechanisms in dopedLaMnO3:Evidence for polaron formation

Transport mechanisms in dopedLaMnO3:Evidence for polaron formation

Crystal and magnetic structure of theLa1−xCaxMnO
Pissas
¹
,
Kallias
²
,
Hofmann³
et al. 2002
Phys. Rev. B
56
1
22
1
View full text Add to dashboard Cite

Disorder effects at low temperatures in La0.7−xYxCa0.3MnO3 manganites

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Thermodynamic and Electron Diffraction Signatures of Charge and Spin Ordering inLa1−xCax

Cited by 446 publications

References 18 publications

Transport mechanisms in dopedLaMnO3:Evidence for polaron formation

Transport mechanisms in dopedLaMnO3:Evidence for polaron formation

Crystal and magnetic structure of theLa1−xCaxMnOPissas1, Kallias2, Hofmann3 et al. 2002Phys. Rev. B561221View full textAdd to dashboardCite

Disorder effects at low temperatures in La0.7−xYxCa0.3MnO3 manganites

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About

Crystal and magnetic structure of theLa1−xCaxMnO
Pissas
¹
,
Kallias
²
,
Hofmann³
et al. 2002
Phys. Rev. B
56
1
22
1
View full text Add to dashboard Cite