A study team, led by LU Qingyou, a professor at High Magnetic Field Laboratory, Chinese Academy of Sciences (CHMFL), designed a new type of magnetic force microscope (MFM) customized for micrometer or even nanometer specimens, through which they directly observed phase separation in a manganite nanowire.

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 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.

A research group led by Prof. ZENG Changgan from University of Science and Technology of China(USTC) 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.

To aim at this problem, customized for this kind of micrometer or even nanometer specimens, LU Qingyou’s group at CHMFL designed a new type of MFM through which the distribution of the magnetic domains was directly imaged. 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 indicated by the arrows shown in Figures 4f,g is about 100 nm.

These observations strongly suggest 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.

Their work entitled Quantum Percolation and Magnetic Nanodroplet States in Electronically Phase-Separated Manganite Nanowires was published in Nano Letters.

Phase diagram and the schematic of the phase evolutions for different states (Imaged by ZHANG Kaixuan)

Topology image and the dependence of the phase separations on magnetic field (Imaged by FENG Qiyuan)