We present the evidence of surface magnetism detection using highly charged ions as a probe, and without any external magnetic field application [1]. This is obtained by x-ray spectroscopy of the n=2à 1 and n=3à 2 transitions from hollow atoms produced by making collide slow Ar17+ and Ar17+ ion beams (Ekin = 160–170 keV) with a monocrystalline nickel sample at various temperatures. When increasing the sample temperature, the x-ray unresolved transitions show an asymmetric broadening to lower energies, indicating a larger electron population of the initial levels (n=2 and 3, respectively). This effect agrees with the expected behaviour of a reduction of the Pauli exclusion effect in the decaying levels (corresponding to a reduction of the Pauli shielding effect recently studied in other systems [2]). This reduction is due to the loss of spin alignment of the captured electrons caused by the change of magnetic phase: from a ferromagnetic phase at low temperature to a paramagnetic one at higher temperature. These findings put an end to a longstanding controversy from contradictory studies on ion–magnetic surface interaction based on Auger spectroscopy [3,4], and open new interesting perspectives for surface characterization. Outlooks on studies of new samples (including 2D materials) and with high-resolution x-ray spectroscopy based on Bragg diffraction will also be presented.
[1] P. Dergham et al., in preparation for Phys. Rev. Lett.
[2] I. Madesis, A. Laoutaris, T.J.M. Zouros et al., Phys. Rev. Lett. 124 113401 (2020)
[3] M. Unipan, A. Robin, R. Morgenstern and R. Hoekstra, Phys. Rev. Lett. 96 177601 (2006)
[4] M. Busch, S. Wethekam and H. Winter, Phys. Rev. A 78 010901 (2008)
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Alexandre Gumberidze - Department Atomic, Quantum & Fundamental Physics