Interplay of magnetocrystalline and magnetoelastic anisotropy in epitaxial <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>Co</mml:mi> <mml:mo>(</mml:mo> <mml:mn>10</mml:mn> <mml:mover accent="true"> <mml:mn>1</mml:mn> <mml:mo>¯</mml:mo> </mml:mover> <mml:mn>0</mml:mn> <mml:mo>)</mml:mo> </mml:mrow> </mml:math> films
Gauravkumar Patel, Fabian Ganss, Lorenzo Fallarino, Gabriel Sellge, Mikel Quintana, René Hübner, D. Sander, Olav Hellwig, K. Lenz, J. Lindner
Abstract
With the goal of creating an in-plane (IP) uniaxial anisotropy system, we deposited a thickness series of epitaxial <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:mrow> <a:mi>Co</a:mi> <a:mo>(</a:mo> <a:mn>10</a:mn> <a:mover accent="true"> <a:mn>1</a:mn> <a:mo>¯</a:mo> </a:mover> <a:mn>0</a:mn> <a:mo>)</a:mo> </a:mrow> </a:math> films grown on Si(110) substrates with Ag(110) and Cr(211) buffer layers by magnetron sputtering. However, quantifying the IP magnetic anisotropy using ferromagnetic resonance measurements revealed a much more complex behavior than expected for a simple uniaxial system like hexagonally close-packed (hcp) Co. To understand the experimental results, an in-depth x-ray diffraction analysis of the film structure was performed. Even at a thickness of 100 nm, it revealed an anisotropic strain in the Co films, mainly within the Co basal plane, while the <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"> <c:mi>c</c:mi> </c:math> axis remained mostly unaffected. Calculations show that such unrelaxed strain induces a significant magnetoelastic anisotropy, which counteracts the magnetocrystalline one and, as a result, reduces the overall effective anisotropy. A detailed analysis revealed that mainly the compressive strain along the <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"> <d:mrow> <d:mi>Co</d:mi> <d:mo>[</d:mo> <d:mn>10</d:mn> <d:mover accent="true"> <d:mn>1</d:mn> <d:mo>¯</d:mo> </d:mover> <d:mn>0</d:mn> <d:mo>]</d:mo> </d:mrow> </d:math> out-of-plane direction is responsible for the observed magnetoelastic anisotropy, while the tensile strain along the <f:math xmlns:f="http://www.w3.org/1998/Math/MathML"> <f:mrow> <f:mi>Co</f:mi> <f:mo>[</f:mo> <f:mover accent="true"> <f:mn>1</f:mn> <f:mo>¯</f:mo> </f:mover> <f:mn>2</f:mn> <f:mover accent="true"> <f:mn>1</f:mn> <f:mo>¯</f:mo> </f:mover> <f:mn>0</f:mn> <f:mo>]</f:mo> </f:mrow> </f:math> IP direction only plays a minor role.