Temperature Dependence of the Exchange Splitting of Fe by Spin-Resolved Photoemission Spectroscopy with Synchrotron Radiation

Abstract

Temperature-induced changes in the electronic structure of Fe(100) have been investigated by spin-and angle-resolved photoemission for temperatures between room temperature and the Curie temperature T c . States nearly stationary in energy (T^r^) have been observed for photon energy hv = 60 eV. However, from a strong increase in minority-spin intensity for hv = 3l and 21 eV, a downwards shift of the AJ band is inferred to occur upon heating towards T c for large k vectors. PACS numbers: 75.50.Bb, 75.10.Lp, 79.60.Cn The electronic structure at finite temperatures of the 3d-transition metals Fe, Co, and Ni is currently a matter of strong theoretical interest. Spinpolarized band theory based on the self-consistent local-density-functional description gives an adequate account of the ferromagnetic ground state (e.g., cohesive energy, nonintegral moments). 1 However, controversial attempts have been made recently to describe transition-metal magnetism at finite temperatures. 2 "" 6 The basic common idea is to try to incorporate into the theory the existence of local magnetic moments even above T c . The ferromagnetic-to-paramagnetic phase transition is then governed by thermal disordering of the moments, requiring much less energy than singleparticle spin flips which would involve energy changes as large as the exchange splitting. The controversy is over the spatial extent of correlation among the magnetic moments, which is connected intimately to the present debate on the existence of spin waves above TQ?The ferromagnetic-to-paramagnetic phase transition of Fe has been studied by spin-unresolved, angle-resolved photoemission. 8 However, only by measuring the electron spin explicitly can exchange-split bands be identified unambiguously and the band dispersions be detected, as will be shown below. Furthermore, the spin dynamics at elevated temperatures, as spin rotations around the spontaneous magnetization direction or flips of local magnetic moments which currently are considered to be the driving force for the phase transition, can be observed only by this method. We have therefore, for the first time, performed a spin-, angle-, and energy-resolved photoemission experiment on temperature-induced changes in the electronic structure of Fe. Because of a predicted wave-vector (k) dependence of the temperature dependence of the exchange splitting, 5,9 we employed monochromatized tunable synchrotron radiation from the German storage ring BESSY, allowing selection of initial states with different k.The experiment is similar to a recent one on Ni(110) 10 using a resonance lamp. Total energy resolution, including the linewidth of light, was 0.4 eV at Ai/ = 60 eV and about 0.3 eV at Ai/ = 31 eV. The angular resolution was about ±3° at hv = 60 eV decreasing to about ±4° at hv = 31 eV, resulting in k resolution of about j-of the Brillouin zone. The sample was cleaned in situ by standard surfaceanalysis techniques and its surface conditions were monitored by low-energy electron diffraction and photoelectron spectroscopy. 11 T...

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

“…Spin polarization measurements [19] for out-of-plane magnetization at T $ T Cb rule out the possibility of canted magnetic moments at these temperatures. A more rapid decrease of the surface spin polarization compared to the bulk is consistent with the observations on other ferromagnetic systems [3][4][5], and also with a recent investigation on Gd [18].…”

“…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.…”

Onset of magnetic order in strongly-correlated systems fromab initioelectronic structure calculations: application to transition metal oxides

“…Of course, when an average is taken over all spin orientations, the electronic structure does not have an overall spin polarization. Nevertheless, it is possible to identify such 'local exchange splitting' experimentally, using photoemission [23] and inverse photoemission [24] techniques. The local moment obtained for the Mn sites in the DLM paramagnetic state differs from that in the ground state by ≈0.03µ B (see table 1).…”

A New Spin on Photoemission Spectroscopy

“…One example of such work is shown in Figure 3.3(a) where normal emission spin-resolved spectra from Fe(100) are shown. 100 The spectra taken well below T C (solid markers) match theory quite well. The spin majority EDC shows two clear peaks corresponding to the Γ 25 and Γ 12 majority bands.…”

“…100,22,24 As discussed in section 3.3, spin-resolved photoemission can measure the exchange splitting of the minority and majority bands and directly confirm the spin character of each. As Fe has the largest exchange splitting of the 3d ferromagnets, it is an ideal system for giving the spin-TOF a 'test-drive'.…”