Tailoring the Spin Reorientation Transition of Co Films by Pd Monolayer Capping

Area of Science:

• Materials Science
• Surface Science
• Magnetism

Background:

• Ultra-thin magnetic films exhibit unique properties dependent on their thickness and substrate.
• Controlling the magnetic anisotropy (easy-axis) is crucial for spintronic device applications.
• Cobalt (Co) films on Ruthenium (Ru(0001)) are a model system for studying interfacial magnetism.

Purpose of the Study:

• To investigate the effect of a palladium (Pd) capping layer on the magnetic easy-axis of ultra-thin Co films grown on Ru(0001).
• To determine the influence of Co film thickness (2-5 atomic layers, AL) on the Pd capping-induced magnetic anisotropy changes.
• To understand the role of surface anisotropy in observed magnetic reorientation phenomena.

Main Methods:

• Fabrication of ultra-thin Co films (2-5 AL) on a Ru(0001) substrate using molecular beam epitaxy.
• Capping the Co films with a monolayer of Pd.
• Characterization of the magnetization easy-axis using techniques sensitive to magnetic anisotropy (e.g., Magneto-Optical Kerr Effect).
• Exposure studies with hydrogen (H2) and carbon monoxide (CO) gases to assess their influence on magnetic alignment.

Main Results:

• A Pd monolayer capping induced a transition from in-plane to out-of-plane magnetization alignment for 3 and 4 AL-thick Co films.
• The 5 AL-thick Co film did not exhibit this magnetic reorientation upon Pd capping.
• The observed changes are attributed to an enhanced surface anisotropy at the Co-Pd interface.
• Exposure to H2, CO, or their combination did not reverse the out-of-plane magnetization induced by the Pd layer.

Conclusions:

• Palladium capping is an effective method to tune the magnetic anisotropy of specific ultra-thin Co films on Ru(0001).
• The thickness-dependent response highlights the delicate balance of interfacial and volume contributions to magnetic anisotropy.
• Surface anisotropy plays a dominant role in the observed magnetic reorientation, which is robust against common gas exposures.