Enhanced magnetoresistance of ultrathin (Au/Co)n multilayers with perpendicular anisotropy

Cyanide-free electrolyte for Au/Co-Au nano-multilayer electrodeposition utilising 5,5-dimethylhydantoin as a complexing agent

A novel cyanide-free electrolyte was used in electrodepositing Au/Co-Au nano-multilayers. Firstly, an optimised electrolyte for Au-Co alloy electrodeposition was obtained from orthogonal experiments. The effect of current density and potential values on the deposited composition was investigated. Results showed that low current density and over-potential value promoted Au deposition. A large current density and high over-potential value resulted in high cobalt concentration. The co-deposition of gold and cobalt in this study system was canonical. When the electrode potential was positive (-0.6 V, -0.7 V vs. saturated calomel electrode (SCE)), only gold was deposited; when the potential was negative (-0.8 V vs. SCE), gold and cobalt were co-deposited. Using an optimised cyanide-free electrolyte produced Au/94.07 at% Co-Au multi-layers with a gold layer of approximately 20 nm and a 94.07 at% Co-Au alloy layer of approximately 90 nm in the 5,5-dimethylhydantoin-containing, cyanide-free system.

Stm Studies of GMR Spin Valves

We have investigated the surface roughness and the grain size in giant magnetoresistance (GMR) spin valve multilayers of the general type: FeMn/Ni80Fe20Co/Cu/Co/Ni80Fe20 on glass and aluminum oxide substrates by scanning tunneling microscopy (STM). The two substrates give very similar results. These polycrystalline GMR multilayers have a tendency to exhibit larger grain size and increased roughness with increasing thickness of the metal layers. Samples deposited at a low substrate temperature (150 K) exhibit smaller grains and less roughness. Valleys between the dome-shaped individual grainsare the dominant form of roughness. This roughness contributes to the ferromagnetic, magnetostatic coupling in these films, an effect termed “orange peel” coupling by Néel. We have calculated the strength of this coupling, based on our STM images, and obtain values generally within about 20% of the experimental values. It appears likely that the ferromagnetic coupling generally attributed to so-called “pinholes” in the Cu when the Cu film thickness is too small is actually “orange peel” coupling caused by these valleys.

First-principles calculations of the structural stability and magnetic property of the metastable phases in the equilibrium immiscible Co-Au system

To reveal the energetic sequence of the alloy phases in the Co-Au system, the lattice constants, cohesive energies, and bulk modulus of the fcc Au, hcp Co, the B1, B2, and L1(0) structured CoAu phases, and the D0(3), L1(2), and D0(19) structured Co(3)Au and CoAu(3) phases, respectively, are acquired by first-principles calculations within the generalized-gradient approximation (GGA) as well as within the local density approximation (LDA). In addition, the magnetic moment of the Co atom in the studied phases are also calculated. To further examine the structural stability, the elastic constants of the studied phases are calculated and the results suggest that the fcc-type structures could be elastically stable at Co/Au = 1:3, 1:1, and 3:1, whereas the hcp-type structures could be stable at Co/Au = 1:3 and 3:1. Moreover, the spatial valence charge density (SVCD) and spin density of the studied phases are also calculated to clarify the physical origin of the structural stability. It turns out that, in the relatively stable phases, the high SVCDs mostly distribute between the similar atoms, thus forming the attractive covalent bonding to stabilize the respective structures, and that the spin density may also play an important role in influencing the stability of the ferromagnetic metastable phases.