A research group led by LU Qingyou at High Magnetic Field Laboratory, Hefei Institutes of Physical Science of Chinese Academy of Sciences, designed a new type of magnetic force microscope (MFM) customized for micrometer or even nanometer specimens, through which researchers directly observed phase separation in a manganite nanowire. The study was published in Nano Letters.

One-dimensional (1D) confinement has been revealed to effectively tune the physical properties of materials in homogeneous states. In contrast to the usually observed homogeneous electronic states, electronic phase separation (EPS) at mesoscopic scale can be stabilized in the so-called electronically soft matters. A prototypical example is doped perovskite manganites.

Previous studies of manganites usually adopted top-down lithography technique to achieve spatial confinement. The very compound nature of manganites introduces complexities at the etched edges, which may affect their properties substantially.

Prof. ZENG Changgan' group at University of Science and Technology of China of Chinese Academy of Sciences prepared edge-free La_0.33Pr_0.34Ca_0.33MnO₃ (LPCMO)/MgO core shell nanowires with superior structural quality by bottom-up method, which offers an ideal platform to investigate the intrinsic transport properties under quasi-1D confinement. However, it is almost impossible to find a nanoscale nanowire (about 70nm in width and 1um in length) in a macroscale substrate (5mm×5mm), using an MFM.

Customized for this kind of micrometer or even nanometer specimens, a new type of MFM which can directly image the distribution of the magnetic domains was designed by researchers. And they unambiguously revealed the onset of magnetic nanodroplet state, a precursor to the ferromagnetic metallic state.

It is noted that there is no direct correlation between the MFM images and the topology image. Moreover, the locations of the insulating domains and their distances change with magnetic field. When the field is altered from 0.03 to 3 T, for example, the distance variation between the two insulating domains is about 100 nm.

These observations strongly suggested that the robustness of the insulating phases under high magnetic field in the low temperature range is not originated from defect pinning and collectively point to an intrinsic origin of quasi-1D confinement.