Magnetostructural\nCorrelations in a Layered Perovskite:\nK<sub>2</sub>CuF<sub>4</sub> at Large Compression

Through a combination of Raman spectroscopy and synchrotron\npowder\nX-ray diffraction measurements supplemented with Density Functional\nTheory calculations, we unravel the pressure response of K<sub>2</sub>CuF<sub>4</sub>, a prototypical 2D ferromagnetic system. Around 10\nGPa sliding of [CuF<sub>4</sub>]<sup>2–</sup><sub>∞</sub> layers leads to a transition from the Ruddlesden–Popper phase\ninto a Dion–Jacobson-like structure. This transition results\nin substantial structural and electronic rearrangement within the\nplanes, resulting in a change from 2D ferromagnetism to 1D antiferromagnetism.\nFurther compression induces tilting distortions that result in the\ntransition into a novel <i>P</i>1̅ phase commencing\nat 15 GPa. The triclinic phase retains the 1D antiferromagnetic character,\nalbeit with an alternating strength of the superexchange interactions.\nWe show that K<sub>2</sub>CuF<sub>4</sub> retains its layered and\nsemiconducting character up to the boundary of its thermodynamic stability.