2020同步年報

The authors then used X-ray absorption spectra (XAS) in situ at TPS 45A1 to determine the valence state of the Pr and Mn ions in the heteroepitaxial films. Figure 2(a) shows the isotropic Pr M 4,5 XAS from the PCMO layer measured at 300 K with that of Pr 2 O 3 , a standard Pr 3+ reference sample. The similar spectral features of the PCMO film and Pr 2 O 3 indicate that Pr ions in the PCMO layer are trivalent. Figure 2(b) shows the isotropic Mn L 2,3 XAS of the PCMO layer and a reference MnO bulk crystal that were measured concurrently in an upstream chamber. As the MnO (Mn 2+ ) spectrum differs from that of the PCMO layer and the signal of MnO of least energy is observed at 639 eV, it showed that PCMO is free of Mn 2+ ions. Further, a direct comparison with the Mn L 2,3 spectra reported earlier for PCMO and La 0.5 Sr 0.5 MnO 3 ( Fig. 2(b) ) showed a clear similarity between the spectrum of PCMO and those of well characterized bulk PCMO and La 0.5 Sr 0.5 MnO 3 . The results thus confirmed that the PCMO thin film consisted of 50%Mn 3+ and 50%Mn 4+ ions, as expected from the nominal stoichiometry. The authors also discussed the me- chanical modulation of the transport properties as shown in Figs. 3(a) and 3(b) , which show the flex-in and flex-out mode magneto-transport measurements with bending radius 5 mm of inward/outward. On appli- cation of the two flexible modes, the melting fields in both cases appeared at magnetic field 5 T. Interestingly, the metal-insulator transition tempera- ture T MI shifted upward in the flex-in mode and downward in the flex-out mode. The results clearly showed that the colossal magnetoresistance (CMR) properties of PCMO can be modulated by mechanical bending. Figure 3(c) shows a summary of the magneto-transport results. The authors observed a large bending- controlled modulation of the CMR ratio, ( R - R 0 )/ R × 100%, achieving nearly 1000% at 110 K. Furthermore, to demonstrate a validity for practical applications, detailed bending tests were performed at room temperature, for which the data exhibited nearly 30% resistive tunability ( Fig. 3(d) ); the resistive tunability is calculated as ( R - R 0 )/ R 0 × 100%. Cycling tests were also measured to show the endurance of PCMO/F/mica properties. The overall results showed excellent stability under both flex-in and flex- out modes at bending radius 5 mm for the PCMO/STO heteroepitaxial films grown on F-mica. 1 (Reported by Ashish Chainani) This report features the work of Ying- Hao Chu and his co-workers published in Adv. Funct. Mater. 30 , 2004597 (2020). TLS 13A1 SW60 − X-ray Scattering • XRD • Materials Science, Condensed-matter Physics TLS 17B1 W200 − X-ray Scattering • XRD • Materials Science, Condensed-matter Physics Physics and Materials Science 017 Fig. 2 : X-ray absorption spectra of a) M-edge of Pr and b) L-edge of Mn of PCMO/STO on F-mica substrates. [Reproduced from Ref. 1] Fig. 3 : Temperature-dependent resistance of a PCMO film on F-mica with (a) flex-in mode and (b) flex-out mode. (c) Temperature-dependent CMR ratios of a sample (thickness 1000 nm) with the flat, flex-in and flex-out modes. (d) Bending-radius-dependent resistive tunability at room temperature. [Reproduced from Ref. 1]