Observation of pressure-induced structural transition in K2CuF4 by phonon-Raman scattering experiments: Change of the orbital ordering by pressure

Since the ferromagnetic intralayer exchange interaction in K2CuF4 is due to the antiferrodistortive (AFD) orbital ordering of the 3d holes of Cu2+ ions, we expect that the ferromagnetism of this compound to disappear when the AFD order of the distortion of CuF6 octahedra collapses. Recent magnetic susceptibility measurements performed at high pressures on this compound actually confirmed the disappearance of the ferromagnetism above approximately 9 GPa [M. Ishizuka ct al.: J. Phys. Sec. Jpn. 65 (1996) 1927]. To obtain evidence of the pressure-induced structural change which corresponds to the magnetic change mentioned above, are measured the pressure dependence of the phonon-Raman spectra of this compound. As a result, we found that the scattering lines relevant to the vibrational modes of CuF6 octahedra ordered in the AFD fashion disappeared above 9 similar to 10 GPa. This result is consistent with the structure above 9 GPa revealed by recent X-ray diffraction experiments that we performed.