Uncovering the path to low-field colossal magnetoresistance: a microscopic view of field driven percolative insulator-to-metal transition in manganites

For perovskite manganites, their colossal magnetoresistance (CMR) requires a large field, which limits their potential applications. In order to uncover the path to achieve low-field CMR, it is crucial to understand the microscopic process of the field driven insulator-to-metal transition (IMT) in manganites. This is particularly true considering the fact that the IMT is of a percolative type, in which the interplay between nucleation and growth of the electronic phase separation domains under magnetic field is not well investigated. In this work, we investigate the magnetic field driven percolative IMT in a model system of La1-x-yPrxCayMnO3 in real space via magnetic force microscopy (MFM). Our experimental observations show unambiguously three stages of the IMT phase transition where domain nucleation and domain growth exhibit distinctly different features in the global initial magnetization measurements. Moreover, MFM reveals that domain growth requires a much lower field than domain nucleation, which provides critical information on how to achieve low-field CMR. It is believed that the exchange field provided by ferromagnetic metallic domains at the boundary with antiferromagnetic insulating domains plays a critical role in assisting the domain growth process. Optimizing such internal exchange fields in manganites is a potential route to achieve CMR without the need of a large external field.