Enhancement of low-field magnetoresistance in self-assembled epitaxial La_0.67 Ca_0.33 MnO₃:NiO and La_0.67 Ca_0.33 MnO₃:Co₃O₄ composite films via polymer-assisted deposition

Polymer-assisted deposition method has been used to fabricate self-assembled epitaxial La_0.67 Ca_0.33 MnO₃:NiO and La_0.67 Ca_0.33 MnO₃:Co₃O₄ films on LaAlO 3 substrates. Compared to pulsed-laser deposition method, polymer-assisted deposition provides a simpler and lower-cost approach to self-assembled composite films with enhanced low-field magnetoresistance effect. After the addition of NiO or Co₃O₄, triangular NiO and tetrahedral Co₃O₄ nanoparticles remain on the surface of La_0.67 Ca_0.33 MnO₃ films. This results in a dramatic increase in resistivity of the films from 0.0061 Ωcm to 0.59 Ωcm and 1.07 Ωcm, and a decrease in metal-insulator transition temperature from 270 K to 180 K and 172 K by the addition of 10%-NiO and 10%-Co₃O₄, respectively. Accordingly, the maximum absolute magnetoresistance value is improved from -44.6% to -59.1% and -52.7% by the addition of 10%-NiO and 10%-Co₃O₄, respectively. The enhanced low-field magnetoresistance property is ascribed to the introduced insulating phase at the grain boundaries. The magnetism is found to be more suppressed for the La_0.67 Ca_0.33 MnO₃:Co₃O₄ composite films than the La_0.67 Ca_0.33 MnO₃:NiO films, which can be attributed to the antiferromagnetic properties of the Co₃O₄ phase. The solution-processed composite films show enhanced low-field magnetoresistance effect which are crucial in practical applications. We expect our polymer-assisted deposited films paving the pathway in the field of hole-doped perovskites with their intrinsic colossal magnetoresistance.