Strong Anisotropy of Projected3dMoments in EpitaxialCrO2Films

Abstract

Soft x-ray magnetic circular dichroism (XMCD) spectra have been investigated for different crystallographic projections of CrO 2 . Strong anisotropic orbital Cr 3d contributions and a change of sign of the XMCD signal is observed and attributed to t 2g majority states near the Fermi level. Additionally, moment analysis exhibits anisotropic behavior in the projected spin contributions of CrO 2 assigned to a strong magnetic dipole term T z , consistent with an intrinsic magnetic easy axis behavior along the CrO 2 [001] axis. A reduced projected isotropic Cr 3d spin moment has been interpreted in terms of hybridization with oxygen. PACS numbers: 75.30.Gw, 78.70.Dm, 87.64.Ni In the past few years, CrO 2 has attracted revived interest due to its remarkably high spin polarization at the Fermi energy, theoretically predicted to be 100% [1][2][3][4] and recently verified by superconducting tunneling spectroscopy at T 18 K [5,6] and spin-polarized photoemission spectroscopy at T 293 K [7]. The reason for this revival is mainly related to promising future applications such as magnetic tunneling and spin injection devices on the basis of CrO 2 electrodes [8]. The oxygen mediated coupling and its half metallic nature are a challenging problem for theoretical investigations, originated by the presence of oxygen hybridization, double exchange, self-doping, and correlation effects [2]. The quantitative influence of orbital moments [9], inner 3d shell spin-orbit coupling, and the magnetic dipole term T z [10] All spectra were recorded in total electron yield mode at the bending-magnet beam line PM I at BESSY II with an energy resolution E͞DE 2000 in an applied magnetic field of 65 kOe (flipped at each data point). The degree of circular polarization was 95%. All spectra have been measured at 80 K. Spectra are carefully background subtracted and edge normalized using the same background and normalization factor for parallel and antiparallel orientation of the photon beam k vector with respect to the sample magnetization. Further details of the experimental setup and data analysis have been published elsewhere [19]. The experimental geometry is schematically shown in the inset of Fig. 1a. X-ray magnetic circular dichroism (XMCD) spectra were taken at fixed grazing incidence (f 60 ± ) and the sample was rotated by the angle q around the surface normal. Figure 1a shows normalized XAS spectra for q 7 ± and Fig. 1b shows the corresponding XMCD signals for nearly a axis (7 ± ), c axis (86 ± ) and intermediate (40 ± ) projected azimuthal sample orientations. Compared to other 3d metal XMCD spectra [20][21][22], very strong and pronounced changes as a function of the azimuthal angle q are present. For c-axis enhanced projection (q 86 ± ) a direct observable change of sign at 587 eV is present. The negative XMCD intensity suggests a strong increase of the projected orbital moment for increased c-axis projections. In contrast only very small changes in the averaged Cr L 2,3 XAS are present and therefore not shown. We have measured q a...

Direct correlation of Cr 3 d orbital polarization and O K -edge X-ray magnetic circular dichroism of epitaxial CrO 2 films

“…A Curie temperature of T c ≈ 385 K has been determined. Nearly no surface contamination of Cr 2 O 3 is present [14,15] which was also reported by other groups [16]. Further details of the sample growth and characterization have been discussed elsewhere [17].…”

Size-induced enhanced magnetoelectric effect and multiferroicity in chromium oxide nanoclusters

“…Its contribution to absorption could be crudely reproduced using a reference XAS spectrum of CrO 2 (ref. 13). This interfacial phase also contributes to the dichroic signal (20%).…”

“…The presence, below the MgO layer containing the clusters, of a 20-nm thick metal film much thicker than the light penetration depth (a few nanometres) excluded any contribution to the recorded spectra from the Cr 3 þ ionic impurities usually present in bulk MgO substrates 39 . The XMCD signal was obtained by combining XAS spectra recorded with left and right circularly polarized lights and applied magnetic fields of þ 6 T and À 6 T. Experimental data were fitted to a linear superposition of reference spectra found in the literature for bulk a-Cr 2 O 3 (XAS) 40 , Cr 3 þ ions in ruby a-Al 2 O 3 :Cr 3 þ (XMCD) 12 and a thick CrO 2 film (XAS and XMCD) 13 .…”

Ising superconductivity and Majorana fermions in transition-metal dichalcogenides

“…If a CrO2 film, which has magnetic easy axis pointing to the out-of-plane directions, is used as the half-metal lead, the spin polarization of CrO2 can be continuously tuned to the in-plane directions by a small in-plane magnetic field [32,33] which will not induce any orbital effects on the Ising superconductor.…”