Biomedical subjects

J B Goodenough

Publications and source records attributed to J B Goodenough.

9 recordsLinked to original sources

PubMed2006

Unusual evolution of the magnetic interactions versus structural distortions in RMnO3 perovskites.

We report the refinement of x-ray powder diffraction together with magnetic and thermal conductivity measurements made on the entire family of RMnO3 perovskites prepared by melt growth or under high pressure. Analysis of the data has identified the origin of the transition from type-A to type-E magnetic order as a competition between t-orbital and e-orbital spin-spin interactions within each Mn-O-Mn bond in the (001) planes, the e-orbital interactions decreasing with decreasing R3+-ion size.

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PubMed2006

Anomalous electronic state in CaCrO3 and SrCrO3.

Comprehensive measurements of electrical transport properties under pressure, thermal conductivity, magnetic susceptibility, and room-temperature compressibility have been used to characterize SrCrO3 and CaCrO3 perovskites synthesized under high pressure. Comparison with other narrow-band perovskite oxides suggests that their anomalous physical properties are correlated with bond-length instabilities caused by the crossover from localized to itinerant electronic behavior.

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PubMed2006

Suppression of ferromagnetic double exchange by vibronic phase segregation.

From Raman spectroscopy, magnetization, and thermal expansion on the system La(2/3)(Ca(1-x)Sr(x))(1/3)MnO3, we have been able to provide a quantitative basis for the heterogeneous electronic model for manganites exhibiting colossal magnetoresistance (CMR). We construct a mean-field model that accounts quantitatively for the measured deviation of T(C)(x) from the T(C) predicted by de Gennes double-exchange in the adiabatic approximation and predicts the occurrence of a first-order transition for a strong coupling regime, in accordance with the experiments. The existence of a temperature interval T(C) < T < T*, where CMR may be found, is discussed in connection with the occurrence of an idealized Griffiths phase.

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PubMed2005

Exchange interaction in the insulating phase of RNiO3.

In order to characterize the spin-spin exchange interactions responsible for the Type-E' antiferromagnetic order in inhomogeneous RNiO3 perovskites (R=Y or rare earth), the pressure dependence of the Néel temperature T(N) was systematically measured for samples with T(N)<T(IM) and T(N)=T(IM); T(IM) is an insulator-metal transition temperature. Analysis of the results shows that, as for superexchange, perturbation theory can be used to describe the interatomic exchange interactions for T(N)<T(IM), but the perturbation theory breaks down where T(N) approaches T(IM).

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PubMed2005

Pressure-induced non-Fermi-liquid behavior of PrNiO3.

Comprehensive temperature scans of the resistivity of a high-quality sample of PrNiO3 were made under different pressures up to 30 kbar; they have revealed that the insulator phase is suppressed completely at P approximately equal to 13 kbar, transforming to a non-Fermi-liquid phase in which the resistivity varies as Deltarho=rho(T)-rho(0) approximately T(n) with n=1.33 and 1.60 over a broad pressure range.

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PubMed2005

Universal octahedral-site distortion in orthorhombic perovskite oxides.

Lattice parameters of the orthorhombic perovskites RMO3 (R=rare earth, M=Ti, V, ..., Ni, and Ga) have been simulated based on the ionic M-O bond length and rigid MO6/2 octahedra. Comparison with experimental data shows that the long-standing lattice-parameter anomaly generally found for the larger R3+ ions in these families is caused by a structural feature that is not revealed by the geometric tolerance factor widely used for the perovskites.

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PubMed2004

Unusually strong orbit-lattice interactions in the RVO3 perovskites.

The thermal conductivity kappa(T) of the RVO3 crystals was measured. At T>T(infinity), RVO3 crystals conduct heat like a glass; the phonon contribution to kappa(T) is completely suppressed by spin and orbital fluctuations. In the interval T(N) T(infinity), a phononlike kappa(T) was observed at T<T(N). This study shows clear-cut evidence of strong orbit-lattice coupling in RVO3 perovskites. Thermal conductivity measurement could be used as a sensitive probe to study orbital ordering.

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PubMed2003

Structural transformation induced by magnetic field and "colossal-like" magnetoresistance response above 313 K in MnAs.

MnAs exhibits a first-order phase transition from a ferromagnetic, high-spin metal hexagonal phase to a paramagnetic, lower-spin insulator orthorhombic phase at T(C)=313 K. Here, we report the results of neutron diffraction experiments showing that an external magnetic field, B, stabilizes the hexagonal phase above T(C). The phase transformation is reversible and constitutes the first demonstration of a bond-breaking transition induced by a magnetic field. The field-induced phase transition is accompanied by an enhanced magnetoresistance of about 17% at 310 K. The phenomenon appears to be similar to that of the colossal magnetoresistance response observed in the Mn [corrected] perovskite family.

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PubMed2002

Pressure-induced transition from localized electron toward band antiferromagnetism in LaMnO(3).

The temperature dependence of the ac susceptibility under pressure has been used to track the Néel temperature T(N) of the Mott insulators LaMnO3, CaMnO3, and YCrO3. Bloch's rule relating T(N) to volume V, viz., alpha=dlog(T(N)/dlog(V=-3.3, is obeyed in YCrO3 and CaMnO3; it fails in LaMnO3. This breakdown is interpreted to be due to a sharp increase in the factor [U(-1)+(2Delta)(-1)] entering the superexchange perturbation formula. A first-order change at 7 kbar indicates that the transition from localized-electron to band magnetism is not smooth.

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