Spin reorientation transitions and structures of electrodeposited Ni/Cu(100) ultrathin films with and without Pb additives

Comparisons of magnetic defects and coercive forces for Co/Si(100) and Co/rubrene/Si(100)

Spintronics can add new functionalities to electronic devices by utilizing the spin degree of freedom of electrons. Investigating magnetic defects is crucial for the performance of spintronics devices. However, the effects of magnetic defects that are introduced by the presence of organic materials on their magnetic properties remain unclear. Herein, we report on a novel method using rubrene combined with Kerr microscopy that enables quantitative and direct measurements of magnetic defect density. For Co/Si(100) at a magnetic field near the coercivity value, Kerr microscopy images show a dark image with some magnetic defects. Because of domain wall motion, small patches gradually change the contrast. These magnetic defects are immovable at different magnetic fields and serve as pinning sites for domain wall motion. Experimental evidence shows that coercive force can be reduced by controlling the magnetic defect density by introducing small amounts of rubrene into the films. Furthermore, direct quantitative measurements of magnetic defects show both a one-dimensional bowing of domain walls and strong defect-domain wall interactions in the films. Based on these findings, we propose a viable strategy for reducing the coercive force of Co/Si(100) by controlling the magnetic defect density and this new information promises to be valuable for future applications of spintronics devices.

Enhancing silicide formation in Ni/Si(111) by Ag-Si particles at the interface

Compound formation at a metal/semiconductor interface plays crucial roles in the properties of many material systems. Applications of Ni silicides span numerous areas and have the potential to be used as new functionalities. However, the magnetic properties of ultrathin Ni layers on silicon surfaces and related chemical compositions at the interface are not fully understood and the influence of Ag additives on the reactivity of Ni/Si(111) remain unclear. We report herein on the fact that the dominant species produced at the interface is NiSi, which is produced by the spontaneous formation of strong bonds between Ni and Si atoms. Assuming that a Ni layer is formed over a NiSi layer with the total coverage as a constraint, we established a chemical shift-related concentration model that, in effect, represents a practical method for determining the amount of ultrathin Ni silicides that are produced at the buried interface. The formation of Ag-Si particles provide a viable strategy for enhancing silicide formation via a specific interaction transfer mechanism, even at room temperature. The mechanism is related to differences in the enthalpies of formation ΔHAg-Si, ΔHNi-Ag, and ΔHNi-Si, for these phases and provides insights into strategies for producing ultrathin silicides at a buried interface.

Enhancing the magnetic anisotropy energy by tuning the contact areas of Ag and Ni at the Ag/Ni interface

Modifying the interfacial conditions of magnetic layers by capping with overlayers can efficiently enhance the magnetic functionality of a material.

Tuning coercive force by adjusting electric potential in solution processed Co/Pt(111) and the mechanism involved

A combination of a solution process and the control of the electric potential for magnetism represents a new approach to operating spintronic devices with a highly controlled efficiency and lower power consumption with reduced production cost. As a paradigmatic example, we investigated Co/Pt(111) in the Bloch-wall regime. The depression in coercive force was detected by applying a negative electric potential in an electrolytic solution. The reversible control of coercive force by varying the electric potential within few hundred millivolts is demonstrated. By changing the electric potential in ferromagnetic layers with smaller thicknesses, the efficiency for controlling the tunable coercive force becomes higher. Assuming that the pinning domains are independent of the applied electric potential, an electric potential tuning-magnetic anisotropy energy model was derived and provided insights into our knowledge of the relation between the electric potential tuning coercive force and the thickness of the ferromagnetic layer. Based on the fact that the coercive force can be tuned by changing the electric potential using a solution process, we developed a novel concept of electric-potential-tuned magnetic recording, resulting in a stable recording media with a high degree of writing ability.

Electrochemical cell for in situ electrodeposition of magnetic thin films in a superconducting quantum interference device magnetometer

An electrochemical cell is designed and applied for in situ electrodeposition of magnetic thin films in a commercial SQUID magnetometer system. The cell is constructed in such a way that any parasitic contribution of the cell and of the substrate for electrodeposition to the magnetic moment of the deposited film is reduced to a minimum. A remanent minor contribution is readily taken into account by a proper analysis of the detected signal. Thus, a precise determination of the absolute magnetic moment of the electrodeposited magnetic film during its growth and dissolution is achieved. The feasibility of the cell design is demonstrated by performing Co electrodeposition using cyclic voltammetry. For an average Co film thickness of (35.6 ± 3.0) atomic layers, a magnetic moment per Co atom of (1.75 ± 0.11) μ(B) was estimated, in good agreement with the literature bulk value.