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  Guo, H.; Li, Z.W.; Chang, C.F.; Hu, Z.; Kuo, C.Y.; Perring, T.G.; Schmidt, W.; Piovano, A.; Schmalzl, K.; Walker, H.C.; Lin, H.J.; Chen, C.T.; Blanco-Canosa, S.; Schlappa, J.; Schüßler-Langeheine, C.; Hansmann, P.; Khomskii, D.I.; Tjeng, L.H.; Komarek, A.C.: Charge disproportionation and nano phase separation in RSrNiO₄. Scientific Reports 10 (2020), p. 18012/1-11

10.1038/s41598-020-74884-2
Open Accesn Version

Abstract:
We have successfully grown centimeter-sized layered RSrNiO4 single crystals under high oxygen pressures of 120–150 bar by the floating zone technique. This enabled us to perform neutron scattering experiments where we observe close to quarter-integer magnetic peaks below ∼77 K that are accompanied by steep upwards dispersing spin excitations. Within the high-frequency Ni–O bond stretching phonon dispersion, a softening at the propagation vector for a checkerboard modulation can be observed. We were able to simulate the magnetic excitation spectra using a model that includes two essential ingredients, namely checkerboard charge disproportionation and nano phase separation. The results thus suggest that charge disproportionation is preferred instead of a Jahn–Teller distortion even for this layered Ni3+ system.