A negative isotropic magnetoresistance effect more than three orders of magnitude larger than the typical giant magnetoresistance of some superlattice films has been observed in thin oxide films of perovskite-like La(0.67)Ca(0.33)MnOx. Epitaxial films that are grown on LaAIO(3) substrates by laser ablation and suitably heat treated exhibit magnetoresistance values as high as 127,000 percent near 77 kelvin and approximately 1300 percent near room temperature. Such a phenomenon could be useful for various magnetic and electric device applications if the observed effects of material processing are optimized. Possible mechanisms for the observed effect are discussed.

Colossal magnetoresistance with more than a thousandfold change in resistivity (ΔR/RH=127 000% at 77 K, H=6 T) has been obtained in epitaxially grown La-Ca-Mn-O thin films. This magnetoresistance value is about three orders of magnitude higher than is typically seen in the giant-magnetoresistance-type metallic, superlattice films. The temperature of peak magnetoresistance is located in the region of metallic resistivity behavior. As the magnetoresistance peak occurs not at the temperature of magnetic transition but at a temperature where the magnetization is still substantial, the spin-disorder scattering is not likely to be the main mechanism in these highly magnetoresistive films. The peak can be shifted to near room temperature by adjusting processing parameters. Near-room-temperature ΔR/RH values of ∼1300% at 260 K and ∼400% at 280 K have been observed. The presence of grain boundaries appears to be very detrimental to achieving large magnetoresistance in the lanthanum manganite compounds. The fact that the electrical resistivity of a material can be manipulated by magnetic field to change by orders of magnitude could be useful for various device applications.

Melt-textured growth of polycrystalline YBa2Cu3O7−δ superconductor using directional solidification created an essentially 100% dense structure consisting of long, needle- or plate-shaped crystals preferentially aligned parallel to the a-b conduction plane. The new microstructure, which completely replaces the previous granular and random structure in the sintered precursor, exhibits dramatically improved transport Jc values at 77 K of ∼17 000 A/cm2 in zero field and ∼4000 A/cm2 at H=1 T (as compared to ∼500 and ∼1 A/cm2, respectively, for the as-sintered structure), with the severe field dependence of Jc (‘‘weak-link’’ problem) no longer evident in the new melt-textured material. The improvement in Jc is attributed to the combined effects of densification, alignment of crystals, and formation of cleaner grain boundaries. Microstructure and distribution of various phases present in the melt-textured material are discussed in relation to the superconducting properties.

A colossal magnetoresistance effect with more than a thousandfold change in resistivity (ΔR/RH=127 000% at 77 K, H=6 T) has been obtained in epitaxially grown La-Ca-Mn-O thin films. The effect is negative and isotropic with respect to the field orientations. The magnetoresistance is strongly temperature dependent, and exhibits a sharp peak that can be shifted to near room temperature by adjusting processing parameters. Near-room-temperature ΔR/RH values of ∼1300% at 260 K and ∼400% at 280 K have been observed. The presence of grain boundaries appears to be detrimental to achieving very large magnetoresistance in the lanthanum manganite films. The orders of magnitude change in electrical resistivity could be useful for various magnetic and electric device applications.

A large magnetoresistance ratio in excess of 10 000% (at 140 K, H=6 T) has been obtained in a sintered perovskitelike material with a composition of La0.60Y0.07Ca0.33MnOx. The doping of La–Ca–Mn–O with Y resulted in a decrease in the lattice parameter by ∼0.2%, and improved the magnetoresistance by an order of magnitude. The fact that such a large magnetoresistance can be obtained in a polycrystalline material implies that an epitaxial film growth may not be necessary for device applications, with fewer restrictions in substrate selection and processing parameters. Low field measurements at 77 K gave a magnetoresistance ratio of ∼6.5% at H=500 Oe in the La–Y–Ca–Mn–O sample.