The magnetic susceptibility of elemental copper (Cu) shows an anomalous rise at low temperatures superimposed on the expected atypical diamagnetic response. Such temperature-dependent susceptibility, which is also known as the Curie tail, cannot be explained on the basis of the Larmor diamagnetic and Pauli paramagnetic contributions expected in Cu. Using valence band resonant photoemission spectroscopy results and density functional theory calculations, we show the magnetic anomaly appears due to the presence of holes in the Cu $3d$ band, which originates from a thermally excited electronic configuration. Our study therefore highlights that the Curie tail, which is generally overlooked presuming it is either due to paramagnetic impurities or defects, can in fact be intrinsic to a material, and even simple systems such as elemental Cu are susceptible to electronic excitations giving rise to an anomalous magnetic state.

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• Density of states
• Magnetic susceptibility
• Magnetism
• Density functional calculations
• X-ray fluorescence holography