Photon Factory Activity Report 2005 #23Part B (2006)
Surface and Interface

7A, 7C/2004G319

Spin reorientation transition in ultrathin Co films on Ru(0001)
induced by Ru capping1

J. Miyawaki1, D. Matsumura2, H. Abe1, T. Otsuki1, E. Sakai1, K. Amemiya1, T. Ohta*1,3
Graduate School of Science, University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
2
Japan Atomic Energy Agency, Sayo-cho, Sayo-gun, Hyogo 679-5198, Japan3
SR center, Ritsumeikan University, Noji-higashi, Kusatsu, Shiga 525-8577, Japan

Introduction
Co/Ru multilayers are well known to show strong
interlayer antiferromagnetic coupling and many studies
have been dedicated to the understanding of that property
from the viewpoints of fundamental physics as well as oftechnological applications[1,2]. Moreover, Co/Ru system
exhibits perpendicular magnetic anisotropy (PMA) and isvery interesting from the viewpoint of magnetic
anisotropy. However, there are few studies about theorigin of PMA and it is still an open question. In thisstudy, magnetism and structure of Co thin films on theRu(0001) single crystal were investigated by x-raymagnetic circular dichroism (XMCD) and x-ray
absorption fine structure (XAFS), and the correlation ofthem is discussed.
Experimental
All the experiments were performed in a UHV
condition. Co was evaporated by the electron-beam
evaporation method with a substrate temperature of 363 K.
Thickness of the films was controlled by the oscillatory
intensity of the RHEED spot.
Co K-edge EXAFS spectra were taken at BL-7C with adouble-crystal Si(111) monochromator detuned by ~40%
at normal (90°) and grazing (30°) x-ray incidence. The
incident x-rays were detected by an ionization chamber
filled with N2 and fluorescent x-rays by a single element
SSD. Co LIII,II-edge XMCD spectra were taken at BL-7A
and obtained by reversing the magnetization of the films.
The remanent magnetization was examined. For thedetection of magnetization, XMCD measurements wereperformed at GI and NI.
Results
From the XMCD measurements, we found that asdeposited Co films show only surface parallel
magnetization in the whole thickness range of theobservation (1-15 ML), while a Ru capping on 1-5 MLCo/Ru(0001) causes a spin reorientation transition fromsurface parallel to perpendicular magnetization. No
significant change of surface parallel magnetic orbital
moment was observed by the Ru capping, indicating thatthe observed spin reorientation transition should be
attributed to the increase of surface perpendicularmagnetic orbital moment.
From the analysis of polarization dependence ofEXAFS spectra, in-plane and out-of-plane Co-Co bond

64

Users' Reportlengths for each Co thickness were obtained (Figure 1).
The strain induced by the substrate and the release of thestrain can be confirmed. For 3 ML Co thin films, theeffect of Ru capping was also investigated (Figure 2).
The Ru capping relaxes the strain in Co thin films as theRu coverage increases. This change of the structure
corresponds to the behaviour of the spin reorientationtransition. The correlation between the origin of PMA andthe stain in Co thin films is thus indicated.

Figure 1: In-plane and out-of-plane Co-Co
bond lengths for each Co thickness.

Figure 2: In-plane and out-of-plane Co-Co bondlength for Ru(x ML)/Co(3 ML)/Ru(0001).
References[1] Y. Huang et al., J. Magn. Magn. Mater. 99 L31 (1991).
[2] S. Hamada et al., J. Magn. Magn. Mater. 240, 539(2002).
* ohta@fc.ritsumei.ac.jp