The perovskite manganites with generic formula RE1?xAExMnO3 (RE = rare earth, AE = Ca, Sr, Ba and Pb) have drawn considerable attention, especially following the discovery of colossal magnetoresistance (CMR). The most fundamental property of these materials is strong correlation between structure, transport and magnetic properties. They exhibit extraordinary large magnetoresistance named CMR in the vicinity of the insulator?metal/paramagnetic?ferromagnetic transition at relatively large applied magnetic fields. However, for applied aspects, occurrence of significant CMR at low applied magnetic fields would be required. This review consists of two sections: in the first section we have extensively reviewed the salient features, e.g.?structure, phase diagram, double-exchange mechanism, Jahn?Teller effect, different types of ordering and phase separation of CMR manganites. The second is devoted to an overview of experimental results on CMR and related magnetotransport characteristics at low magnetic fields for various doped manganites having natural grain boundaries such as polycrystalline, nanocrystalline bulk and films, manganite-based composites and intrinsically layered manganites, and artificial grain boundaries such as bicrystal, step-edge and laser-patterned junctions. Some other potential magnetoresistive materials, e.g.?pyrochlores, chalcogenides, ruthenates, diluted magnetic semiconductors, magnetic tunnel junctions, nanocontacts etc, are also briefly dealt with. The review concludes with an overview of grain-boundary-induced low field magnetotransport behavior and prospects for possible applications.

https://iopscience.iop.org/article/10.1088/0953-8984/20/27/273201/pdf

Low field magnetotransport in manganites

The perovskite manganites of general formula RE_1-xAe_xMnO_3 (RE= rare earth,AE=Ca, Sr, Ba and Pb)have drawn considerable attention, especially following the discovery of colossal magnetoresistance (CMR). They exhibit extraordinary large magnetoresistance pronounced as CMR in the vicinity of insulator-metal/paramagnetic-ferromagnetic transition at a relatively large applied magnetic fields. However, for applied aspectes, occurence of significant CMR at low applied magnetic fields would be required. This review consists of of two sections: In the first section we have extensively reviewed the salient features e.g. structure, phase diagram, double exchange mechansim, Jahn Teller effect, different types of ordering and phase separation of CMR mangnaites. The second is devoted to an overview of experimental results on CMR and related magnetotransport characteristics at low magnetic fields for doped manganites such as polycrystalline La_0.67Ca_0.33MnO_3 films, Ag admixed La_0.67Ca_0.33MnO_3 films, polycrystalline (La_0.7Ca_0.2Ba_0.1MnO_3)and epitaxial (La_0.67Ca_0.33MnO_3) films on different substrates, nanophasic La_0.7Ca_0.3MnO_3, mangnaite-polymer composites (La_0.7Ba_0.2Sr_0.1MnO_3-PMMA and La_0.67Ca_0.33MnO_3-PMMA)and double layered polycrystalline (La_1.4Ca_1.6-xBa_xMn_2O_7) and films (La_1.4Ca_1.6Mn_2O_7). Some other potential magnetoresistive materials e.g. pyrochlores, chalcogenides, ruthenates, diluted magnetic semiconductors, magnetic tunnel junctions, nanocontacts etc have aslo been briefly dealt with. The review concludes with the summary of results for low field magnetotransport behaviour and prospectes for applications.

Low Field Magnetotransport in Manganites

We have fabricated MgxZn1−xO epitaxial composition spreads where the composition across the chip is linearly varied from ZnO to MgO. By using a scanning x-ray microdiffractometer and transmission electron microscopy, we have mapped the phase evolution across the spread. We have discovered a unique growth relationship between cubic and hexagonal MgxZn1−xO where their basal planes are coincident in the phase-separated region of the phase diagram where 0.37⩽x⩽0.6. The continuously changing band gap across the spread is used as a basis for compact broadband photodetector arrays with a range of detection wavelengths separately active at different locations on the spread film. The composition-spread photodetector is demonstrated in the wavelength range of 290–380 nm using the ZnO to Mg0.4Zn0.6O region of the spread.

Monolithic multichannel ultraviolet detector arrays and continuous phase evolution in MgxZn1−xO composition spreads

Combinatorial approaches as effective tools in the study of phase diagrams and composition-structure-property relationships

Tetradecafluorosexithiophene: the first perfluorinated oligothiophene.

Highly correlated electronic systems—such as transition-metal oxides that are doped Mott insulators—are complex systems which exhibit puzzling phenomena, including high-temperature superconductivity and colossal magnetoresistivity Recent studies1,2,3 suggest that in such systems collective electronic phenomena are important, arising from long-range Coulomb interactions and magnetic effects The qualitative behaviour of these systems is strongly dependent on charge filling (the level of doping) and the lattice constant Here we report a time-efficient and systematic experimental approach for studying the phase diagrams of condensed-matter systems It involves the continuous mapping of the physical properties of epitaxial thin films of perovskite manganites (a class of doped Mott insulator) as their composition is varied We discover evidence that suggests the presence of phase boundaries of electronic origin at room temperature

Room-temperature electronic phase transitions in the continuous phase diagrams of perovskite manganites

The combinatorial material chip strategy is used to study the ferroelectric-paraelectric phase boundary of the Ba1−xSrxTiO3 thin film system. The electro-optic (EO) effect at different compositions is measured using a modified direct-current/alternating-current birefringence EO measurement technique. We find that Ba1−xSrxTiO3 thin films exhibit relaxor like behavior with diffused ferroelectric domains existing well past the previously defined ferroelectric-paraelectric boundary (x>0.3).

Jing-Wei Li

Papers

Room-temperature electronic phase transitions in the continuous phase diagrams of perovskite manganites

Electro-optic measurements of the ferroelectric-paraelectric boundary in Ba1−xSrxTiO3 materials chips