Temperature Dependence of the Exchange Splitting of the Surface State on Gd(0001): Evidence against Spin-Mixing Behavior

Weschke, E.; Schüßler-Langeheine, C.; Meier, Robert J.; Fedorov, A. V.; Starke, K.; Hübinger, F.; Kaindl, G.

doi:10.1103/physrevlett.77.3415

Cited by 74 publications

(66 citation statements)

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“…For ferromagnetic Gd metal only the majority component S ↑ of the d-derived Gd(0001) surface state is occupied [12], as is shown by the angle-resolved PE spectrum in Fig. 1(b).…”

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“…For the present investigation we chose the (0001) surface of ferromagnetic hcp Gd metal where the exchange interaction is known to separate majority and minority branches of the d-derived surface state by several hundred meV [12]. With this substantial exchange splitting a limitation in previous studies of non-magnetic systems is avoided, where the Rashba splitting of a state, in order to be resolved, must be larger than its intrinsic (lifetime) width [7].…”

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Rashba effect at magnetic metal surfaces

et al. 2005

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We give experimental and theoretical evidence of the Rashba effect at the magnetic rare-earth metal surface Gd(0001). The Rashba effect is substantially enhanced and the Rashba parameter changes its sign when a metal-oxide surface layer is formed. The experimental observations are quantitatively described by ab initio calculations that give a detailed account of the near-surface charge density gradients causing the Rashba effect. Since the sign of the Rashba splitting depends on the magnetization direction, the findings open up new opportunities for the study of surface and interface magnetism.PACS numbers: 71.70. Ej, A key issue in condensed-matter research aiming at future spintronic devices [1] is to control and manipulate the electron spin in a two-dimensional electron gas (2DEG) of semiconductor systems without the need of applying an external magnetic field. Rashba had realized early on [2] that this can be achieved by an electric field which acts as a magnetic field in the rest frame of a moving electron. The interaction between the spin s of a moving electron of momentumhk with an electric field oriented along the z-axis e z is described by the Rashba HamiltonianThe Rashba parameter α R is proportional to the electric field and depends on the effective, material-dependent spin-orbit coupling (SOC) strength. In nonmagnetic systems the Rashba effect lifts the spin-degeneracy of the energy dispersion ǫ(k) of an electronic state, and the energy difference between ǫ ↑ (k) and ǫ ↓ (k) is called Rashba splitting ∆ǫ(k) = α R |k|. Even though spintronic research currently focuses on spin-polarized electrons in semiconductors [3,4], it is important to explore the Rashba effect in other material classes as well. A necessary condition for the Rashba effect to occur is the absence of inversion symmetry and, while in the proposed FET-type spin transistor [5] a gate voltage must be applied to break inversion symmetry of the 2DEG, this condition is naturally fulfilled by the structural inversion asymmetry (SIA) existing at any crystal surface or interface. Owing to SIA, electrons in a two-dimensional surface or interface state experience an effective crystal potential gradient perpendicular to their plane of propagation, hereby optimizing (e z × k) in Eq. (1). One should expect that the Rashba effect is a general surface and interface phenomenon, but up to now Rashba splittings have only been observed for surface states at Au(111) [6,7] and W(110) [8,9]. Recently relativistic density functional theory (DFT) calculations were able to reproduce the observed splitting of the Au sp-like surface state [10] and the analogy to a 2DEG has been pointed out [11]. Yet, it is still a challenging task to give a physical picture of the Rashba effect from the electronic structure point of view.This Letter presents the first experimental and theoretical evidence of a Rashba splitting of exchange-split two-dimensional electron states. Using the surface state of ferromagnetic Gd metal as example we report on the novel finding of a k-depe...

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“…For ferromagnetic Gd metal only the majority component S ↑ of the d-derived Gd(0001) surface state is occupied [12], as is shown by the angle-resolved PE spectrum in Fig. 1(b).…”

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Rashba effect at magnetic metal surfaces

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“…A scanning tunneling spectroscopy study reports the persistence of the surface state exchange splitting, D surface ex , at and above T Cb [12]. PES and IPES studies on the surface states reached strongly contrasting conclusions, ranging from pure spin mixing to Stoner behavior [9,13,14].While most attention has been devoted to the finite temperature behavior of the localized surface states, the bulk bands have been until now indisputably believed to follow a Stoner behavior. In the present study, we investigate the temperature dependence of Gd bulk and surface states by means of spin-resolved photoemission spectroscopy.…”

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Novel Sb Induced Reconstruction of the (113) Surface of Ge

et al. 2002

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The temperature dependence of the rare-earth valence bands has been regarded as a realization of the Stoner behavior. The exchange splitting of the electronic states appears to scale as the magnetic order parameter for T , T C and to vanish at T T C . We report here a spin-resolved photoemission study on the evolution of Gd bulk bands for 0.5 # T ͞T C # 1. The spin-polarized spectral line shapes display a complex temperature dependence, which clearly contrasts with the interpretation of previous experimental results. The spin-resolved photoemission data demonstrate the inadequacy of the Stoner model to the description of magnetism in rare earths. DOI: 10.1103/PhysRevLett.88.167205 PACS numbers: 75.70.Ak, 75.25. +z, 79.60.Bm Understanding the relation between electronic and magnetic properties at finite temperatures is a central question for many branches of solid state physics. While the electronic theory accurately accounts for the ground state properties of magnetic materials, it meets only limited success in describing their finite temperature behavior, such as the magnetic phase transitions, the corresponding ordering temperatures, and critical parameters.Two simple models are usually considered to schematically describe the finite temperature behavior of the electronic structure, depending on the degree of the electron localization. The Stoner model [1] predicts that the exchange splitting of delocalized states parallels the temperature dependence of the magnetization. In this case, the exchange-split electronic subbands gradually merge together and become degenerate at the Curie temperature, T C . The spin-mixing model [2], on the other hand, describes strongly localized systems where thermal fluctuations of the local magnetic moment directions reduce the magnetization, but leave the magnitude of the local moments and the local electronic structure unchanged. Thus, the exchange splitting of the electronic states does not vary according to this model, while the characteristic spin polarization of the states is gradually lost on approaching T C .Several experimental studies have examined the finite temperature magnetism in the elemental ferromagnets. The itinerant 3d-transition metals (Fe, Co, and Ni) show an intermediate behavior. The complexity of the temperature dependent effects on the electronic structure in these systems defies any simple description [3][4][5]. Rare earths, on the other hand, provide a different and apparently simpler scenario. The magnetic moment in these systems primarily originates from the unfilled 4f subshell, which displays a simple spin-mixing behavior due to its atomiclike character. The magnetic coupling between the 4f moments occurs via the highly delocalized (5d6s)-valence states [6]. Various investigations by spin-integrated photoemission spectroscopy (PES) and inverse photoemission spectroscopy (IPES) report that the exchange splitting of the bulk valence bands vanishes at T C [7][8][9][10][11]. These experimental results have been interpreted as a first evidence for t...

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