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1 Jun 2001

Volume 89, Issue 11, pp. 5815-7704

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Neutron and x-ray evidence of charge melting in ferromagnetic layered colossal magnetoresistance manganites (invited)

L. Vasiliu-Doloc, R. Osborn, S. Rosenkranz, J. Mesot, J. F. Mitchell, S. K. Sinha, O. H. Seeck, J. W. Lynn, and Z. Islam

J. Appl. Phys. 89, 6840 (2001); http://dx.doi.org/10.1063/1.1365256 (6 pages) | Cited 2 times

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Recent x-ray and neutron scattering studies have revealed static diffuse scattering due to polarons in the paramagnetic phase of the colossal magnetoresistive manganites La2−2xSr1+2xMn2O7, with x=0.40 and 0.44. We show that the polarons exhibit short-range incommensurate correlations that grow with decreasing temperature, but disappear abruptly at the combined ferromagnetic and metal–insulator transition in the x=0.40 system because of the sudden charge delocalization, while persisting at low temperature in the antiferromagnetic x=0.44 system. The “melting” of the polaron ordering as we cool through TC occurs with the collapse of the polaron scattering itself in the x=0.40 system. This short-range polaron order is characterized by an ordering wave vector q=(0.3,0,1) that is almost independent of x for x⩾0.38, and is consistent with a model of disordered stripes. © 2001 American Institute of Physics.
Show PACS
75.47.Gk Colossal magnetoresistance
75.50.Dd Nonmetallic ferromagnetic materials
71.30.+h Metal-insulator transitions and other electronic transitions
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
71.38.-k Polarons and electron-phonon interactions

Charge correlations in the magnetoresistive oxide La0.7Ca0.3MnO3 (invited)

J. W. Lynn, C. P. Adams, Y. M. Mukovskii, A. A. Arsenov, and D. A. Shulyatev

J. Appl. Phys. 89, 6846 (2001); http://dx.doi.org/10.1063/1.1358331 (5 pages) | Cited 8 times

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Neutron scattering has been used to study the nature of the spin dynamics and charge correlations in a single crystal of the colossal magnetoresistive perovskite La0.7Ca0.3MnO3. Diffuse scattering from lattice polarons develops as the Curie temperature is approached from below, along with short range polaron correlations that are consistent with stripe formation. Magnetic fields are found to suppress this polaron formation. The temperature dependence of the polaron correlations follows the same behavior as both the resistivity and the anomalous quasielastic component in the magnetic fluctuation spectrum, indicating that they have a common origin. © 2001 American Institute of Physics.
Show PACS
75.47.Gk Colossal magnetoresistance
75.30.Ds Spin waves
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
71.38.-k Polarons and electron-phonon interactions
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Dd Nonmetallic ferromagnetic materials

Evidence for competing order parameters in the paramagnetic phase of layered manganites (invited)

A. Berger, J. F. Mitchell, D. J. Miller, and S. D. Bader

J. Appl. Phys. 89, 6851 (2001); http://dx.doi.org/10.1063/1.1360681 (6 pages) | Cited 7 times

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The magnetic field and temperature dependence of the magnetic susceptibility is studied for the ferromagnetic layered manganites SrO(La1−xSrxMnO3)2 in the composition range x=0.32–0.40. In the paramagnetic phase, the susceptibility exhibits an anomalous maximum at an intermediate magnetic field value. The size of this field-induced susceptibility enhancement increases dramatically with x from 10% for x=0.32 to 160% for x=0.40. The temperature dependence of the effect shows a maximum at T≈1.1 TC for all x. Quantitative analysis in terms of the Landau theory of phase transitions enables us to identify a distortion of the free energy F in the paramagnetic phase that is associated with the susceptibility anomaly. This free energy distortion corresponds to a magnetic system that approaches a first order magnetic phase transition as the temperature is lowered toward TC. Such a behavior is indicative of a second, competing order parameter, which is identified as the recently observed charge density wave. In the immediate vicinity of TC, the anomaly disappears and the system seems to undergo a more conventional second order paramagnetic–ferromagnetic phase transition. © 2001 American Institute of Physics.
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75.20.Ck Nonmetals
75.30.Cr Saturation moments and magnetic susceptibilities
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Relaxor behavior in manganites (invited)

T. Kimura, Y. Tokura, R. Kumai, Y. Okimoto, and Y. Tomioka

J. Appl. Phys. 89, 6857 (2001); http://dx.doi.org/10.1063/1.1362644 (6 pages) | Cited 5 times

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The impurity (Cr3+)-doping effect on the stability of charge and orbital ordering has been systematically investigated for Nd1/2Ca1/2Mn1−yCryO3 crystals by measurements of magnetotransport and x-ray diffraction. The random field in terms of eg orbital deficiencies on the Cr sites drives the charge and orbital correlations to dynamical and short range, which is most relevant to the high-resistive state exhibiting colossal magnetoresistance. In the Cr-doped manganite, we can observe the coexistence of ferromagnetic–metallic and charge–orbital ordered phases, their spatial distributions, diffuse x-ray scattering, magnetic-field annealing, and the aging effect on the magnetic and electric properties, etc. These phenomena are reminiscent of those of relaxor ferroelectrics composed of ferroelectric clusters embedded in a paraelectric matrix. We propose that the mixed-valent manganite can be viewed as a “magneto- and electrorelaxor.” © 2001 American Institute of Physics.
Show PACS
75.47.Gk Colossal magnetoresistance
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Mb Valence fluctuation, Kondo lattice, and heavy-fermion phenomena
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
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