2020同步年報

H eteroepitaxial flexible oxides exhibit many interest- ing properties that make them strong candidates for next-generation flexible electronic devices. 1-5 Recent stud- ies have shown that fluorophlogopite mica (F-mica, also called common mica or muscovite) is a suitable substrate for growing such heteroepitaxial oxides because of its excellent flexibility and high-temperature stability required for applications. For example, superior performance was demonstrated for transparent conductive indium tin oxide, 2 aluminium-doped ZnO, 3 ferroelectric BaTiO 3 , 4 ferromagnet- ic SrRuO 3 , 5 etc . grown on F-mica substrates. Perovskite manganite Pr 0.5 Ca 0.5 MnO 3 (PCMO) in its bulk form exhibits an antiferromagnetic/charge-ordered (AFM/ CO) phase that can be melted on the application of a mag- netic field, but the melting field required for bulk samples is large (~27 T), impeding practical applications. A major im- provement was the growth of PCMO films on SrTiO 3 (STO) substrates, which resulted in decreasing the melting field to 5 T. With the aim of investigating mechanical control of the properties of the PCMO/STO heteroepitaxial oxide system, researchers have now grown PCMO/STO heteroepitaxial films on F-mica. 1 Fig. 1 : (a) Schematic graph of epitaxial structure of PCMO/F-mica and (b) enlarged surficial region showing a nanocolumn structure. XRD analyses of PCMO/F-mica including (c) normal scan of (00L) series of F-mica with PCMO (111) and (222), (d) omega scan of PCMO (111), (e) phi scans of F-mica (202), STO (002), and PCMO (002) and (f) Reciprocal-space mapping of F-mica (202) with STO (002) and PCMO (002). [Reproduced from Ref. 1] The authors used pulsed-laser deposition to grow a buffer STO layer on F-mica, followed by PCMO films on the STO, as shown schematically in Figs. 1(a) and 1(b) . Synchrotron- based X-ray diffraction was implemented on TLS 13A1 and TLS 17B1 at the NSRRC in order to characterize the crystal structure and epitaxy of the PCMO/STO films. The out-of- plane normal scan clearly showed the pristine phase of PCMO, STO and F-mica substrate with only signals in the (111) series of PCMO and STO appearing, along with (00L) signals of F-mica ( Fig. 1(c) ). Further, as shown in Fig. 1(d) , the omega scan of PCMO exhibited full width 0.72° at half maximum, indicating crystallinity of the PCMO layer better than in earlier work. Phi scans were also employed by the authors to study the in-plane structural quality of the films. Figure 1(e) shows that signals corresponding to PCMO (002), STO (002) and F-mica (202) were detected every 60°, showing well aligned six-fold symmetry, confirming the ex- cellent heteroepitaxy. XRD reciprocal-space mapping (RSM) of PCMO (002), STO (002) and F-mica (202) signals agreed with the results from the Phi scans, indicating strain-free films of PCMO and STO layers consistent with the normal scan data. 016 ACTIVITY REPORT 2020 Bending a Colossal Magnetoresistance A new combination of heteroepitaxial Pr 0.5 Ca 0.5 MnO 3 /SrTiO 3 grown on F-mica, shows that excellent mechanical modulation of CMR, in the range ~1000%, can be achieved at low temperature.