ABSTRACT
A decrease of eight orders of magnitude in the resistance of (La0.5Ca0.5)zMnO3 has been detected when the electronic density is kept constant while the calcium content is modified by introducing cationic vacancies. This effect is related to the disappearance of the charge ordering state and the emergence of an antiferromagneticferromagnetic transition. Moreover, high values of the colossal magnetoresistance above room temperature are attained.
Subject(s)
Electrons , Manganese Compounds/chemistry , Calcium/chemistry , Magnetic Phenomena , Oxides/chemistry , TemperatureABSTRACT
We experimentally show that it is possible to induce room-temperature ferromagnetic-like behavior in ZnO nanoparticles without doping with magnetic impurities but simply inducing an alteration of their electronic configuration. Capping ZnO nanoparticles ( approximately 10 nm size) with different organic molecules produces an alteration of their electronic configuration that depends on the particular molecule, as evidenced by photoluminescence and X-ray absorption spectroscopies and altering their magnetic properties that varies from diamagnetic to ferromagnetic-like behavior.
Subject(s)
Crystallization/methods , Magnetics , Nanostructures/chemistry , Nanostructures/ultrastructure , Nanotechnology/methods , Zinc Oxide/chemistry , Macromolecular Substances/chemistry , Materials Testing , Molecular Conformation , Particle Size , Surface PropertiesABSTRACT
In this Letter, we experimentally show that the room temperature ferromagnetism in the Mn-Zn-O system recently observed is associated with the coexistence of Mn(3+) and Mn(4+) via a double-exchange mechanism. The presence of the ZnO around MnO(2) modifies the kinetics of MnO(2)-->Mn(2)O(3) reduction and favors the coexistence of both Mn oxidation states. The ferromagnetic phase is associated with the interface formed at the Zn diffusion front into Mn oxide, corroborated by preparing thin film multilayers that exhibit saturation magnetization 2 orders of magnitude higher than bulk samples.