Abstract
The magnetic properties and the atomic scale morphology of bimetallic two-dimensional nanoislands, epitaxially grown on fcc(111) metal surfaces, have been studied by means of Magneto-Optical Kerr Effect and Scanning Tunneling Microscopy. We investigate the effect on blocking temperature of one-dimensional interlines appearing in core-shell structures, of two-dimensional interfaces created by capping, and of random alloying. The islands are grown on Pt(111) and contain a Co-core, surrounded by Ag, Rh, and Pd shells, or capped by Pd. The largest effect is obtained by Pd capping, increasing the blocking temperature by a factor of three compared to pure Co islands. In addition, for Co-core Fe-shell and Co-core FexCo1−x-shell islands, self-assembled into well ordered superlattices on Au(11,12,12) vicinal surfaces, we find a strong enhancement of the blocking temperature compared to pure Co islands of the same size. These ultra-high-density (15 Tdots/in2) superlattices of CoFe nanodots, only 500 atoms in size, have blocking temperature exceeding 100 K. Our findings open new possibilities to tailor the magnetic properties of nanoislands.
Highlights
Academic Editors: Imre Bakonyi andThe increasing quantity of data generated requires a concomitant increase in storage capacity
The measurements were performed in an ultra-high vacuum (UHV) chamber equipped with a variable-temperature scanning tunneling microscopy (STM) and an in-situ magneto-optical Kerr effect (MOKE) [25]
The blocking temperature Tb is defined as the maximum of χ00 ( T )
Summary
The increasing quantity of data generated requires a concomitant increase in storage capacity. While charge-based flash memories have replaced hard disk drives (HDD) in personal computers, magnetic information storage remains the primary choice for large quantities of data. One of the main challenges in magnetic information storage is to increase the bit density without running into the superparamagnetic limit, where the magnetization reverses by thermal excitation [1,2]. This forces one to chose materials with high magnetic anisotropy energy (MAE) per atom, which requires large switching fields
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