Angle-dependent x-ray absorption spectroscopy in strong magnetic fields is shown to yield precise site specific information about spin and orbital moments in highly anisotropic 3d transition metal systems.A new angle averaging spin sum rule allows for the separate determination of spin and magnetic dipole moments in lower than cubic site symmetry.The microscopic origin of the magnetocrystalline anisotropy can be probed directly through the angular dependence of the orbital moment. PACS numbers: 75.30.Gw, 75.50.Rr, 78.20.Ls The understanding of magnetic phenomena in thin transition metal films and multilayers, like giant magnetoresistance [1] and perpendicular magnetic anisotropy [2 -4], would be greatly aided by a better knowledge of the microscopic magnetic properties of the materials.Of key importance is the reliable measurement of element specific magnetic spin and orbital moments and their anisotropies. In thin magnetic films, and at interfaces and surfaces, all these properties are expected to significantly differ from those in the bulk [3 -5]. In practice, however, the quantitative determination of magnetic moments and their anisotropies is anything but simple. Over the last few years x-ray magnetic circular dichroism (XMCD) spectroscopy has shown great promise as a quantitative magnetometry tool. In contrast to most other techniques, it offers element and site specificity, and the ability to separate the spin and orbital contributions to the magnetic moment by use of powerful theoretical sum rules derived in an atomic framework [6,7]. The sum rules have been tested by band structure calculations [8,9] and have been verified experimentally for bulk Fe and Co [10]. While the orbital magnetic moment is directly linked to the measured dichroism intensity [6], the determination of the spin moment is complicated by the presence of a correction term, the magnetic dipole moment [7], which is known to be sizable in ultrathin films and at surfaces [9]. So far, the presence of this term has appeared to limit the quantitative sum rule determination of spin moments to crystal sites of cubic symmetry.The present paper shows that, for 3d transition metals, the spin and magnetic dipole contributions to the XMCD spin sum rule can be separately determined, for sites with lower than cubic symmetry, i.e. , for all cases with important magnetic dipole contributions to the local magnetic moment.In particular, a new sum rule is derived for the spin moment only, based on the angular average of XMCD intensities in an external magnetic field, oriented along Cartesian axes, sufficiently strong to magnetically saturate the sample along all directions. The angle averaged XMCD spin sum rule holds remarkably well for 3d transition metals and offers exciting new capabilities for the study of the anisotropic magnetic properties of ultra thin films, surfaces, and interfaces. The spin and magnetic dipole moments can now be quantitatively determined by sum rule analysis of experimental spectra and compared with moments obtained from electro...

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In Fig. 10, the labels ''J ab '' and ''J c '' were interchanged. The correct figure along with the original caption appears below. FIG. 10. Exchange interaction in LaMnO 3 with the full Hamiltonian, i.e., with J H ϭ1 eV and with t 2g hopping included. The intraplane and interplane exchanges, J ab and J c , correspond to the e g -e g Ј and e g Ј-e g Ј orbital orientations, respectively. PHYSICAL REVIEW B 68, 029901͑E͒ ͑2003͒