Exchange Bias Effect and Suppression of Charge Ordering Induced by a Surface Phase Separation in La0.25Ca0.75MnO3 Nanowires

The microstructure and magnetic properties of the polycrystalline La 0.25 Ca 0.75 MnO 3 nanowires with diameter of about 60 nm prepared by a sol−gel template method were studied with use of X-ray diffraction, transmission electron microscopy, and superconducting quantum interference device magnetometry. Compared with the robust charge ordering (CO) state with CO transition temperature T CO ≈ 240 K in the bulk counterpart, the CO is suppressed with T CO ≈ 138 K and CO transition becomes wide, at the same time the ferromagnetic (FM) cluster glass state and the exchange bias effect are detected in La 0.25 Ca 0.75 MnO 3 nanowires. This exotic behavior is attributed to the uncompensated surface spins which change the spin configuration of nanowires and enhance the e g charge density at the surface compared to bulk compound and thereby induce the FM cluster glass state as well as exchange bias effect, and weaken the CO.