Electrochemical Tuning of Magnetism in Nanoporous Systems - Oxidation, Hydrogenation and Surface Charging

Nanoporous materials have attracted considerable interest in the scientific community as functional materials with a broad variety of applications, including catalysis and sensing. Owed to their high surface-to-volume ratios it is possible to alter bulk properties via surface modifications.

Electrochemical reactions represent a versatile method to achieve defined surface states with controlled chemical composition and charging state. Magnetic properties of metals and alloys are highly sensitive to both chemical environment and electronic structure, which motivated our investigations.

Metal and alloy electrodes were prepared via electrochemical dealloying, a selective dissolution process from binary or ternary alloys, respectively. By exposing the precursor to an etching agent, the least noble component of the alloy is gradually removed, while enhancing the surface diffusivity of the more noble compound(s) [1]. Appropriate processing conditions enable the formation of nanoporous structures, with the main benefit being adjustable pore sizes. Nanoporous palladium (npPd) and nanoporous copper-nickel alloys (npCuNi) were used as model systems, amongst other promising candidates.

Magnetic tuning experiments were performed in an electrochemical cell, designed for special use in a SQUID (Superconducting Quantum Interference Device) magnetometer. This enables sensitive in situ measurements of the changes in magnetic moment upon various electrochemical treatments and a direct assignment of chemical reactions to magnetic behaviour [2].

Alterations of the magnetic moment of more than 20% were measured for npCuNi upon surface oxidation in aqueous electrolyte, which will be discussed in terms of a perturbation of the magnetic order of the nickel atoms. Furthermore, changes in magnetisation upon surface charging and hydrogenation of npPd are presented.

This work is financially supported by the Austrian Science Fund (FWF): P30070-N36.

[1] I. McCue et al., Ann. Rev. Mater. Res. 46 (2016) 263
[2] E.-M. Steyskal et al., Beilst. J. Nanotech. 4 (2013) 394