Ferromagnetic ground state in La
 0.5
 Ca
 0.5
 MnO
 3
 thin films

Nyeanchi, Emmanuel B.; Krylov, Igor; Zhu, Xiaomei; N.Jacobs,

doi:10.1209/epl/i1999-00470-4

Cited by 12 publications

(7 citation statements)

References 21 publications

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“…when there is a large amount of strained grain boundary material present [37]. Similarly, a strained epitaxial film of La 0.5 Ca 0.5 M nO 3 was found to posess a FMM ground state [38], but this strain must be of the correct type [39]. These experiments demonstrate the important role of strain, which is expanded upon below and in the next sections on Landau theory.…”

Section: Phase Separation and Coexistencementioning

confidence: 98%

“…Twinning may also be avoided by recourse to thin films. Remarkably, the proportions of two coexisting phases can be easily "tweaked" by external parameters that include pressure [51], magnetic fields [52], temperature [33,46], these three parameters together [53], strain [38], electrical currents [54] and X-ray [55] or electron illumination [56].…”

Section: Phase Separation and Coexistencementioning

confidence: 99%

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The self-organised phases of manganites

Mathur

Littlewood

2001

Solid State Communications

116

113

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Self-organisation requires a multi-component system. In turn, a multi-component system requires that there exist conditions in which more than one component is robust enough to survive. This is the case in the manganites because the free energies of surprisingly dissimilar competing states can be similar -- even in continuous systems that are chemically homogeneous. Here we describe the basic physics of the manganites and the nature of the competing phases. Using Landau theory we speculate on the exotic textures that may be created on a mesoscopic length scale of several unit cells.Comment: Review article and speculation. To appear in a special issue of Solid State Communications on MESOSPIN. New version includes fresh experimental evidence in support of charge melting between stripe domains (thanks to V. Kiryukhin -- see sentence and two new references added at end of section 4.2

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Section: Phase Separation and Coexistencementioning

confidence: 98%

Section: Phase Separation and Coexistencementioning

confidence: 99%

The self-organised phases of manganites

Mathur

Littlewood

2001

Solid State Communications

116

113

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“…However, experiments have also indicated that long ranged strain plays an important role. Insulating ordered phases appearing in bulk La 0.5 Ca 0.5 MnO 3 are suppressed in thin films 4 ; it is argued that the difference arises from the lattice mismatch with the substrate, which prevents the occurrence of lattice distortions necessary to accommodate orbital ordering. Similar conclusions have been drawn from recent work on Pr 0.6 Ca 0.4 MnO 3 films subjected both to compressive and tensile strain.…”

Section: Perovskitementioning

confidence: 99%

Strain selection of charge and orbital ordering patterns in half-doped manganites

2003

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Theoretical and computational results are presented clarifying the role of long-ranged strain interactions in determining the charge and orbital ordering in colossal magnetoresistance manganites. The strain energy contribution is found to be of order 20 − 30 meV /M n and in particular stabilizes the anomalous 'zig-zag chain' order observed in many half-doped manganites.Perovskite manganites of chemical formula Ln 1−x Ak x MnO 3 (Ln is a lanthanide rare earth such as La or Pr; Ak is a divalent alkali such as Sr or Ca) present a complex phase diagram associated with the interplay of charge, spin, orbital and lattice degrees of freedom.1 Charge and orbitally ordered phases appear in wide parameter ranges, for example in La 1−x Ca x MnO 3 for x ≥ 0.5, and in Pr 1−x Ca x MnO 3 for 0.3 ≤ x ≤ 0.7. The physical mechanism underlying the ordering remains the subject of debate. Particular attention has focussed on the half-doped (x = 0.5) materials, including La 0.5 Ca 0.5 MnO 3 , Pr 0.5 Ca 0.5 MnO 3 and Nd 0.5 Sr 0.5 MnO 3 , which possess a strongly insulating ground state with a particularly interesting ('zig-zag chain') spin, charge and orbital ordering pattern shown in the inset to Fig. 1a. Stabilizing this state requires 'second neighbor' interactions, which as noted by Khomskii and Kugel 2 and by Ahn and Millis 3 may reasonably be expected to arise from electron-lattice interactions. However, experiments have also indicated that long ranged strain plays an important role. Insulating ordered phases appearing in bulk La 0.5 Ca 0.5 MnO 3 are suppressed in thin films 4 ; it is argued that the difference arises from the lattice mismatch with the substrate, which prevents the occurrence of lattice distortions necessary to accommodate orbital ordering. Similar conclusions have been drawn from recent work on Pr 0.6 Ca 0.4 MnO 3 films subjected both to compressive and tensile strain.5 Other sets of experiments in polycrystalline La 0.5 Ca 0.5 MnO 3 show that the charge/orbital ordering transition temperature is progressively suppressed as grain size is decreased; the interpretation again is that boundary effects inhibit the formation, in small grains, of the strains imposed by the orbital ordering.6 Perhaps most significantly, polarized optical microscopy studies on Bi 0.2 Ca 0.8 MnO 3 single crystals 7 reveal that as temperature is decreased to just below the charge/orbital ordering transition, lenticular shaped domains appear and grow slowly with time. This behavior is well known in martensitic systems 8 , where it is attributed to the interplay between a tendency of the system to favor a state with large strain, and a boundary condition which prevents the existence of a truly uniform strain.Despite the considerable experimental evidence that long ranged strain is important, strain physics has not received much theoretical attention. The original analyses 9,10,11 and many subsequent works 12,13,14 focused on local interactions, including magnetic, Coulomb and Jahn-Teller electron-phonon coupling. In this paper we study lon...

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“…The sample was examined in a Philips CM30 microscope and was cooled to 90 K using a Gatan liquid nitrogen stage. The uniaxial stripe phase was identified via superlattice reflections in a selected area TEM diffraction pattern (illustrated below in Figure 2a); these reflections are detectable at 190 K, reaching a stable form at 90 K. (Note that previous resistivity measurements of thin film La 0.5 Ca 0.5 MnO 3 have failed to produce consistent results 11,12,13 , because of the difficulty of producing high quality films and a failure to check for the superstructure using a microscopic technique. )…”

mentioning

confidence: 99%

Sliding charge-density wave in manganites

et al. 2007

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The so-called stripe phase of the manganites is an important example of the complex behaviour of metal oxides, and has long been interpreted as the localisation of charge at atomic sites 1,2,3,4 . Here, we demonstrate via resistance measurements on La 0.50 Ca 0.50 MnO 3 that this state is in fact a prototypical charge density wave (CDW) which undergoes collective transport. Dramatic resistance hysteresis effects and broadband noise properties are observed, both of which are typical of sliding CDW systems. Moreover, the high levels of disorder typical of manganites result in behaviour similar to that of well-known disordered CDW materials. Our discovery that the manganite superstructure is a CDW shows that unusual transport and structural properties do not require exotic physics, but can emerge when a well-understood phase (the CDW) coexists with disorder.The stripe phase in manganites of the form La 1−x Ca x MnO 3 appears as the temperature is lowered through T ≃ 240 K, and the superstructure wavevector settles on a final value of q≃ (1 − x)a * 1 (where a * is the reciprocal lattice vector) for 0.5 ≤ x < 0.85, at T ≃ 120 K 2 . Based on the insulating nature of the manganites up to room temperature, and the observation of stripes of charge order in transmission electron microscopy (TEM) images, early studies concluded that the superstructure arose from localisation of charge at atomic sites 3,4 . However, neutron and xray studies found the degree of charge localisation at Mn sites to be small, and subsequent theoretical work suggested that a CDW model may be more applicable 5 . This suggestion is supported by the observation that q/a * is strongly temperature dependent 2,6 , indicating that a model in which the superstructure periodicity is derived from the sample stoichiometry cannot be valid. In addition, heat capacity peaks at the transition to the stripe phase can be modelled as "dirty Peierls transitions", expected in a disordered CDW system 7 . However, the possibility of the stripe phase exhibiting sliding behaviour, as seen in many other CDW systems 8 , could not be probed without the ability to make orientation-dependent resistivity measurements. Here we describe the first such measurements on the manganite stripe phase, which reveal dramatic

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Ferromagnetic ground state in La _0.5 Ca _0.5 MnO ₃ thin films

Cited by 12 publications

References 21 publications

The self-organised phases of manganites

The self-organised phases of manganites

Strain selection of charge and orbital ordering patterns in half-doped manganites

Sliding charge-density wave in manganites

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Ferromagnetic ground state in La 0.5 Ca 0.5 MnO 3 thin films

Cited by 12 publications

References 21 publications

The self-organised phases of manganites

The self-organised phases of manganites

Strain selection of charge and orbital ordering patterns in half-doped manganites

Sliding charge-density wave in manganites

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Ferromagnetic ground state in La _0.5 Ca _0.5 MnO ₃ thin films