Spatially Resolved Magnetic Anisotropy of Cobalt Nanostructures on the Au(111) Surface

Abstract

Understanding the origin of perpendicular magnetic anisotropy in surface-supported nanoclusters is crucial for fundamental research as well as data storage applications. Here, we investigate the perpendicular magnetic anisotropy energy (MAE) of bilayer cobalt islands on Au(111) substrate using spin-polarized scanning tunneling microscopy at 4.6 K and first-principles theoretical calculations. Au(111) substrate serves as an excellent model system to study the effect of nucleation site and stacking sequence on MAE. Our measurements reveal that the MAE of bilayer islands depends strongly on the crystallographic stacking of the two Co layers and nucleation of the third layer. Moreover, the MAE of Co atoms on Au(111) is enhanced by a factor of 1.75 as compared to that reported on Cu(111). Our first-principles calculations attribute this enhancement to the large spin-orbit coupling of the Au atoms. Our results highlight the strong impact of nanometer-scale structural changes in Co islands on MAE and emphasize the importance of spatially resolved measurements for the magnetic characterization of surface-supported nanostructures.

Retraction of Magnetic Hysteresis of Single-Molecule Magnets Adsorbed on Ferromagnetic Substrate

“…Both the blue and the red curves have two symmetric, large changes corresponding to the flipping of the tip (B ≈ 0 T) and the Co island (B = ±3T) magnetizations. Similar butterfly-shaped hysteresis loops were reported for the Co bilayers islands on Au(111) 25 and on Cu(111). 26−28 Our observations clearly establish that the bilayer Co islands on Au(111) exhibit single-domain, magnetically bistable states with large coercivity.…”

“…The magnetic properties of these Co islands were probed using a Pt/Ir tip after in situ capture of a cobalt cluster from the surface. 25 These tips were found to be superparamagnetic in nature, and the tip magnetization direction is aligned out-of-plane by application of a small external magnetic field. 25 We first examine the spin-polarized conductance using the single-point scanning tunneling spectroscopy (STS) measurement over Co islands and determine the sample bias voltage to obtain the largest spin contrast.…”

“…25 These tips were found to be superparamagnetic in nature, and the tip magnetization direction is aligned out-of-plane by application of a small external magnetic field. 25 We first examine the spin-polarized conductance using the single-point scanning tunneling spectroscopy (STS) measurement over Co islands and determine the sample bias voltage to obtain the largest spin contrast. Note that the dI/dV contrast is determined by the band structure of the sample at the energy used for the tunneling.…”

“…It is known that the perimeter of the triangle island is aligned either with [101̅ ], [01̅ 1], and [11̅ 0] directions, which is reproduced in Figure 2(a). 25 Also, the crystallographic orientation inside the Co bilayer island is aligned with that of the Au(111) substrate owing to the epitaxial growth of the Co bilayer. 25 The orientations of the TbPc 2 molecules are analyzed using the symmetry lines shown in the figure, which can be seen for the molecules 1 to 4 in Figure 2(a).…”

Reduction in magnetic coercivity of Co nanomagnets by Fe alloying

“…Spin-polarized scanning tunneling microscopy (SP-STM) has been proven the ideal instrument to investigate nano-and atomic-size magnetic structures on surfaces [4][5][6]. Several efforts have been made to resolve the magnetization reversal of elemental nanomagnets [3,[7][8][9][10][11]. In the case of thin films, on the other hand, introduction of alloy composition is one of the most commonly applied techniques for manipulating their magnetic properties.…”