Abstract
The competition among different phases in perovskite manganites is pronounced since their energies are very close under the interplay of charge, spin, orbital and lattice degrees of freedom. To reveal the roles of underlying interactions, many efforts have been devoted towards directly imaging phase transitions at microscopic scales. Here we show images of the charge-ordered insulator (COI) phase transition from a pure ferromagnetic metal with reducing field or increasing temperature in a strained phase-separated manganite film, using a home-built magnetic force microscope. Compared with the COI melting transition, this reverse transition is sharp, cooperative and martensitic-like with astonishingly unique yet diverse morphologies. The COI domains show variable-dimensional growth at different temperatures and their distribution can illustrate the delicate balance of the underlying interactions in manganites. Our findings also display how phase domain engineering is possible and how the phase competition can be tuned in a controllable manner.
Highlights
The competition among different phases in perovskite manganites is pronounced since their energies are very close under the interplay of charge, spin, orbital and lattice degrees of freedom
The phase separation (PS) regime below TAFI can be further divided into the charge-ordered insulator (COI)-dominated PS (COI-PS), the FMMdominated PS (FMM-PS) and the frozen states[7,19,22]
For this type of film, in addition to the anisotropic epitaxial strain stemming from the substrate there exist accommodation strains due to a structural mismatch at the interfaces between the ferromagnetic metal (FMM) and COI phase domains[9,11,22,24,25,26]
Summary
The competition among different phases in perovskite manganites is pronounced since their energies are very close under the interplay of charge, spin, orbital and lattice degrees of freedom. We show images of the charge-ordered insulator (COI) phase transition from a pure ferromagnetic metal with reducing field or increasing temperature in a strained phase-separated manganite film, using a home-built magnetic force microscope. 15) and LPCMO16, has surpringly never been imaged at microscopic scales, possibly due to a larger melting field needed[14,15] We label this field-driven reversed transition of COI as FR for convenience. In addition to the melting process, the COI phase transitions from a magnetic-field-induced saturated FMM state as functions of magnetic field (H) and temperature (T) in a single sample are imaged using a home-built MFM, which features a home-designed scan head housed in a 20 T superconducting magnet These results would substantially increase our understanding of PC in manganites, which may extend to other similar materials
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