Spin Excitations of Individual Fe Atoms on Pt(111): Impact of the Site-Dependent Giant Substrate Polarization

Abstract

We demonstrate using inelastic scanning tunneling spectroscopy and simulations based on density functional theory that the amplitude and sign of the magnetic anisotropy energy for a single Fe atom adsorbed onto the Pt(111) surface can be manipulated by modifying the adatom binding site. Since the magnitude of the measured anisotropy is remarkably small, up to an order of magnitude smaller than previously reported, electron-hole excitations are weak and thus the spin excitation exhibits long lived precessional lifetimes compared to the values found for the same adatom on noble metal surfaces.

Origin of Perpendicular Magnetic Anisotropy and Large Orbital Moment in Fe Atoms on MgO

“…The total anisotropy barrier of Fe atoms on MgO is, therefore, strongly enhanced with respect to Fe films on MgO [1,2,13-16] due to the reduced in-plane coordination of the Fe atoms [23]. Remarkably, it is more than twice the largest value reported for individual Fe atoms adsorbed on other surfaces [21,[66][67][68] and embedded in bulk MgO [17][18][19], and the barrier approaches that reported for Fe atoms in linear molecules [30].…”

Extremely long-lived magnetic excitations in supported Fe chains

“…In particular, the direct measurements, adapted to long time scales, revealed extremely long lifetimes, up to a few hours, for the Fe chains, that quickly increase in the even chain case as the chain length increases 14 . One can also mention measurements of excitation profiles 26,27,28 ; indeed a finite lifetime leads to broadening of the peaks in an excitation spectrum. However, there are other sources of broadening besides experimental effects (e.g.…”

Theoretical probing of inelastic spin-excitations in adatoms on surfaces

“…It is only when the magnetic field is large enough to completely reorient the magnetic moment out-of-plane that one recovers the usual linear behavior of the resonance energy versus magnetic field (see Ref. [6]). …”

“…Indeed, the experiments reported in Ref. [6] show that Fe adatoms on Pt(111) exhibit a very low MAE and long precessional lifetimes, and moreover that these properties are strongly dependent on which hollow site an adatom occupies (fcc or hcp, according to how they stack with respect to the sub-surface Pt layer). In contrast, those reported in Ref.…”

“…Refs. [2][3][4][5][6][7][8][9][10]), and with which many of the predictions of Douglas L. Mills were verified. Understanding the excitation and the dynamical behavior of such nano-magnetic systems is naturally a topic of prime importance, actively studied recently both to provide insight into fundamental aspects of magnetism and as possible elements for future information technology.…”