Tailoring ultrathin magnetic multilayers at terraced topologically insulating interfaces for perpendicularly magnetized domains

Topological insulators and skyrmion-hosting, chiral magnetic multilayers are two well-explored areas of modern condensed matter physics, each offering unique advantages for spintronics applications. In this paper, we demonstrate the optimization process for the growth of a <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:mrow> <a:msub> <a:mi>Bi</a:mi> <a:mn>2</a:mn> </a:msub> <a:msub> <a:mi>Se</a:mi> <a:mn>3</a:mn> </a:msub> <a:mo>/</a:mo> </a:mrow> <a:mrow> <a:mtext>buffer</a:mtext> <a:mo>/</a:mo> <a:msub> <a:mrow> <a:mo>[</a:mo> <a:mi>Pt</a:mi> <a:mo>/</a:mo> <a:mi>CoB</a:mi> <a:mo>/</a:mo> <a:mi>Ru</a:mi> <a:mo>]</a:mo> </a:mrow> <a:mrow> <a:mo>×</a:mo> <a:mi>N</a:mi> </a:mrow> </a:msub> </a:mrow> </a:math> heterostructure that combines these two material classes: the <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"> <b:mrow> <b:msub> <b:mi>Bi</b:mi> <b:mn>2</b:mn> </b:msub> <b:msub> <b:mi>Se</b:mi> <b:mn>3</b:mn> </b:msub> </b:mrow> </b:math> epilayer was grown by molecular beam epitaxy before transfer under ultrahigh vacuum to a separate growth chamber where the polycrystalline metallic multilayer was sputter deposited. The structure of the samples was characterized by cofitted x-ray and polarized neutron reflectometry measurements and scanning transmission electron microscopy. Polarized neutron models and standard magnetometry show that a buffer layer exceeding a critical thickness is required to obtain the desired uniform, perpendicular magnetic anisotropy in every magnetic layer in the multilayer. Samples with both Ta and Mo buffers were used requiring thicknesses of 1.5 and 0.9 nm, respectively. In minimizing the <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"> <c:mrow> <c:msub> <c:mi>Bi</c:mi> <c:mn>2</c:mn> </c:msub> <c:msub> <c:mi>Se</c:mi> <c:mn>3</c:mn> </c:msub> </c:mrow> </c:math> terracing, buffered samples yield well-defined, out-of-plane, magnetic domains suitable for spin-orbit torque-induced manipulation as determined by x-ray photoemission electron microscopy.