Subject Number : S-16-MS-2018
Support Type : Collaborative research
Proposal Title (English) : XMCD Study of a Relation between the Perpendicular Magnetic Anisotropy and Interface Spin-Orbit Interaction of Au/Fe/MgO and Ag/Fe/MgO Films
Username (English) : Sh. Yamamoto and I. Matsuda
Affiliation (English) : Institute for Solid State Physics, The University of Tokyo, Japan

1. Summary
Interface magnetism has been one of the central topics for investigating fundamental magnetic properties. They range from the relation between the dimensionality and the magnetic structure to the control of magnetism by the electric field rather than by electric current or magnetic field. Thinner magnetic film systems have a larger contribution from the interface to the magnetism. Furthermore, it is expected that an interfacial spin-orbit interaction enhances the perpendicular magnetic anisotropy (PMA) of magnetic layers. However the effect of spin-orbit interaction on interface magnetism has not been investigated systematically so far. In the present research, we synthesized heterostructures that contained sub-nanometer thick Fe films and measured spectra of X-ray magneto circular dichroism.

2. Experimental
In our previous study, we have investigated interfacial perpendicular magnetic anisotropy (PMA) energy of an ultrathin magnetic system, Au/Fe/Au, comparing with a reference system, MgO/Fe/Au. By utilizing a torque magnetometer, it was revealed that PMA energy in the Au/Fe/Au system had a smaller interfacial PMA energy (455 J/cm2) than that in the MgO/Fe/Au system (696 J/cm2). In order to reveal the origin of the interfacial PMA for both systems, we measured thickness dependence of Fe 2p X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) at BL4B in UVSOR.

3. Results and Discussion
Measurements were conducted with a total-electron yield mode at 10 K. The samples were cooled down with a liquid He. External magnetic field, ± 2 T was applied parallel to the incident light. The sample surface was perpendicular to the incident light. The XAS (XMCD) was extracted from the sum (difference) of absorption spectra measured under applying positive and negative external field. By applying the magneto-optical sum-rule for 2p edge XMCD, the spin and orbital magnetic moment were extracted. It indicated that in both systems, larger orbital moments were observed with reducing Fe film thickness with respect to the value of bulk bcc Fe. On the other hand, the spin magnetic moment does not depend on the Fe film compared to the orbital moment. It was shown that the PMA originates from the orbital moment in both systems. The variation of orbital magnetic moment of Au/Fe/Au was smaller than that of MgO/Fe/Au system, which was consistent with our previous measurements of interfacial PMA energy.

4. Others
N/A

5. Publication/Presentation
[1] 山本真吾他、第40回日本磁気学会学術講演会、2016年9月6日
[2] 山本真吾他、第30回日本放射光学会年会、2017年1月9日

6. Patent
N/A