Ferromagnetic insulating state in manganites:<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow /><mml:mrow><mml:mn>55</mml:mn></mml:mrow></mml:msup></mml:mrow><mml:mi mathvariant="normal">Mn</mml:mi></mml:math>NMR study

Savosta, M. M.; Kamenev, V. I.; Бородин, В. А.; Novák, P.; Maryško, M.; Hejtmánek, J.; Dörr, K.; Sahana, M.

doi:10.1103/physrevb.67.094403

Cited by 23 publications

(16 citation statements)

References 28 publications

(41 reference statements)

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“…In the case of FMI regions the mechanism of the spin-spin relaxation is different than in the case of the FMM regions and is assigned to fluctuations of the magnetic hyperfine field and the electric-field gradient ͑EFG͒ related to the motion of the Jahn-Teller polarons. 44 According to the model proposed by Savosta et al 44 the charge carriers in the FMI regions can be regarded as the small Jahn-Teller polarons, and their movement is accompanied by a lattice excitation leading to a fluctuation of the EFG. The T 2 of nuclei in the FMI regions was found to be shorter than T 2 of nuclei in the FMM state in several pseudocubic perovskite manganites, for example, in La 1−␦ MnO 3 ͑Ref.…”

Section: Spin-spin Relaxation Ratesmentioning

confidence: 99%

M55nnuclear magnetic resonance study of highly Sr-dopedLa2−2<

et al. 2008

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The 55 Mn nuclear magnetic resonance ͑NMR͒ study of bilayered perovskites La 2−2x Sr 1+2x Mn 2 O 7 with 0.5 Յ x Յ 1 is presented. The 55 Mn spin-echo spectra were measured at 4.2 K at zero applied magnetic field and at fields up to 2.5 T. Recent neutron-diffraction studies report that all the compounds studied are antiferromagnetically ordered ͑except x = 0.68 in which no long-range magnetic order was found͒ ͓Mitchell et al., J. Phys. Chem. B 105, 10731 ͑2001͔͒. However, within the doping range 0.62Յ x Յ 0.68, apart from NMR signal from antiferromagnetic insulating ͑AFI͒ phase, also lines from ferromagnetic insulating ͑FMI͒ and ferromagnetic metallic ͑FMM͒ phases are observed. This indicates that phase separation occurs in high Sr-doped bilayered manganites. The amount of the FMI and FMM regions decreases with the Sr doping level and for compounds with x = 0.75 and x = 0.8; only the line originating from nuclei in Mn 4+ cations in AFI regions is observed.

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Section: Spin-spin Relaxation Ratesmentioning

confidence: 99%

M55nnuclear magnetic resonance study of highly Sr-dopedLa2−2<

et al. 2008

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“…10 and 24, setting a lower bound for the temperature where the polaron clusters start to form ͑T clusters Ͼ 776 K͒. At very low T, the fraction of the u environment reaches a remanent value ͑f u o Ϸ 10% ͒, which is typically observed in CMR manganites 25 and is a signature of the ferromagnetic-metallic ͑FMM͒ and FMI phase coexistence. When the temperature changes, f u ͑symmetrically f d ͒ suffers a smooth variation leading from an undistorted to a JTdistorted dominant microscopic environment.…”

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confidence: 99%

“…The competition of the distinct dynamics of the u ͑fast hopping͒ and d ͑related to polaronic conduction͒ environments is responsible for the macroscopic ferromagnetic insulator behavior observed in these systems. 25 Below T c , both local environments become ferromagnetic and a phase coexistence between metallic ͑u͒ and insulator ͑d͒ regions exists. However, the majority fraction ͑d͒ is characterized by the ultraslow diffusion of charge carriers imposing an overall insulator behavior.…”

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confidence: 99%

Percolative transition on ferromagnetic insulator manganites: Uncorrelated to correlated polaron clusters

et al. 2006

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We report an atomic-scale study on the ferromagnetic insulator manganite LaMnO 3.12 using ␥-␥ perturbed angular correlation spectroscopy. Data analysis reveals a nanoscopic transition from an undistorted to a JahnTeller ͑JT͒ distorted local environment upon cooling. The percolation thresholds of the two local environments enclose a macroscopic structural transition ͑rhombohedral-orthorhombic͒. Two distinct regimes of JT distortions were found: a high-temperature regime where uncorrelated polaron clusters with severe distortions of the Mn 3+ O 6 octahedra survive up to T Ϸ 800 K and a low-temperature regime where correlated regions have a weaker JT-distorted symmetry. DOI: 10.1103/PhysRevB.73.100408 PACS number͑s͒: 75.47.Lx, 31.30.Gs, 64.60.Ak, 76.80.ϩy Intense experimental and theoretical work has been devoted to manganite systems due to their colossal magnetoresistance ͑CMR͒, polaron dynamics, and charge-orbital ordering phenomena. The undoped manganites ͑AMnO 3 where A is a trivalent ion of La, Pr, . . .͒ typically show antiferromagnetic insulator behavior and cooperative Jahn-Teller ͑JT͒ distortion of MnO 6 octahedra. Oxygen excess or the presence of divalent ions at A sites reduce the static JT distortion by the creation of Mn 4+ ions. This effect favors the ferromagnetic interaction via dynamic electron transfer between Mn 3+ and Mn 4+ , the so-called double-exchange ͑DE͒ interaction. 1 Although DE interaction explains qualitatively the CMR, it does not fully account for the large resistivity of the paramagnetic and ferromagnetic insulator phases. Polaron formation must certainly play an important role in this respect. [2][3][4][5] Polarons are formed due to the strong electron-lattice coupling that leads to charge localization via JT distortions. Recently, the nature of such local distortions, their dynamics and correlations have been addressed by several authors. [6][7][8][9][10][11] In spite of such an effort, several issues as the detailed structure of polarons, the temperature evolution of polaron clusters, or the effect of such evolution on the average macroscopic lattice structure still remain as open questions.Local distortions and their dynamics can be studied by using ␥-␥ perturbed angular correlation spectroscopy ͑PAC͒, a nuclear hyperfine method specially effective to sample atomic-scale environments. PAC efficiency is T independent, allowing us to explore a wide range of temperatures. To gain further insight on the microscopic nature of polaronic distortions, their spatial correlations, and the role of polarons in ferromagnetic insulator manganites ͑FMI͒, we have studied in detail the compound LaMnO 3.12 using the PAC technique. This compound is a prototypical FMI manganite that undergoes a rhombohedral ͑R͒-orthorhombic ͑O͒ structural transition around room temperature, which provides us with an ideal scenario to probe the evolution of local lattice distortions through different average lattice symmetries. In particular, we show that random distributed polaron clusters survive in the undist...

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“…55 Mn NMR spectra of (Pr x Sr 1Àx )MnO 3 [26,27] and some other manganese oxides [28] show the two-phase character of these materials in the vicinity of a first-order phase transition. Fig.…”

Section: Magnetic Properties In the DC And Ac Magnetic Fieldsmentioning

confidence: 98%