RESUMO
Using X-ray emission spectroscopy, we find appreciable local magnetic moments until 30 GPa to 40 GPa in the high-pressure phase of iron; however, no magnetic order is detected with neutron powder diffraction down to 1.8 K, contrary to previous predictions. Our first-principles calculations reveal a "spin-smectic" state lower in energy than previous results. This state forms antiferromagnetic bilayers separated by null spin bilayers, which allows a complete relaxation of the inherent frustration of antiferromagnetism on a hexagonal close-packed lattice. The magnetic bilayers are likely orientationally disordered, owing to the soft interlayer excitations and the near-degeneracy with other smectic phases. This possible lack of long-range correlation agrees with the null results from neutron powder diffraction. An orientationally disordered, spin-smectic state resolves previously perceived contradictions in high-pressure iron and could be integral to explaining its puzzling superconductivity.
RESUMO
By moving individual Fe-porphyrin-based molecules with the tip of a scanning tunneling microscope in the vicinity of the elbow of the herringbone-reconstructed Au(111) containing a Br atom, we reversibly and continuously control their magnetic state. Several regimes are obtained experimentally and explored theoretically: from the integer spin limit, through intermediate magnetic states with renormalized magnetic anisotropy, until the Kondo-screened regime, corresponding to a progressive increase of charge fluctuations and mixed valency due to an increase in the interaction of the molecular Fe states with the substrate Fermi sea. Our study demonstrates the potential of utilizing charge fluctuations to generate and tune quantum magnetic states in molecule-surface hybrids.