Spin resolved photoelectron spectroscopy of Fe₃O₄: the case against half-metallicity

Abstract

Many materials have been theoretically predicted to be half-metallic, and hence suitable for use as pure spin sources in spintronic devices. Yet to date, remarkably few of these predictions have been experimentally verified. We have used spin polarized photoelectron spectroscopy to study one candidate half-metallic system, Fe(3)O(4). Such experiments are normally hampered by difficulties in producing clean stoichiometric surfaces with a polarization that is truly representative of that of the bulk. However, by utilizing higher photon energies than have traditionally been used for such experiments, we can study polarization in 'as received' samples, essentially 'looking through' the disrupted surface. High quality, strain relieved, ex situ prepared Fe(3)O(4) films have been thoroughly characterized by diffraction, transport and magnetometry studies of their crystallographic, electronic and magnetic properties. The spectroscopic results are found to agree fairly closely with previously published experimental data on in situ grown thin films and cleaved single crystals. However, despite the higher photoelectron kinetic energies of the experiment, it has not been possible to observe 100% polarization at the Fermi level. Hence, our data do not support the claim of true half-metallicity for Fe(3)O(4).

CVD synthesis of polycrystalline magnetite thin films: structural, magnetic and magnetotransport properties

“…Because of its abovementioned intrinsic characteristics, magnetite is one of the most interesting materials for application as ferromagnetic (oxide) layer into spintronic devices [4]. Even though very high P values (-80 %) have been observed in epitaxial magnetite films [5], the possibility to obtain full spin polarization in this material is still disputed [4,6]. The large number of recent publications on this topic underlines the high interest in this material [5][6][7][8][9][10][11][12][13][14][15][16], but the practical achievement of (the expected) high performances in functional spintronic devices like magnetic tunnel junctions (MTJ) incorporating Fe 3 O 4 has not been reached yet [9][10][11]13].…”

Scanning Tunneling Microscopy Study of an Altered Fe₃O₄(001) Thin Films Surface by Hydrogen Adsorption

“…The electronic and electron spin states for surface Fe cations differ from ones for bulk Fe cations since there is no Fe atoms to be bonded above the surface Fe cations. In fact, theoretical and experimental electron spin polarization measurements of a clean Fe 3 O 4 (001) surface have shown much lower values than expected [5][6][7][8][9][10][11][12].…”

“…4(c) suggests that there is no obvious difference for the emergence between these sites. We also performed the same investigations concerning two types of O N sites within [1][2][3][4][5][6][7][8][9][10] atomic rows. Although each of these O N sites is equivalent to either O N1 site or O N2 site, the correspondence is unclear due to antiphase domain boundaries introduced in the films.…”

Tailoring the Interface Properties of Magnetite for Spintronics

“…By including spin sensitive Mott detector [52], the fraction of spin-up and spin-down electrons at the Fermi level can be calculated. However, the measured values of the spin polarization in Fe 3 O 4 vary wildly from group to group, and from sample to sample, with reported values ranging from 20-80% [53][54][55][56]. Thus, for several years there has been confusion and debate regarding the real spin polarization of Fe 3 O 4 .…”