Evolution of superparamagnetism in the electrochemical dealloying process

M Gößler,H Schröttner,E.-M Steyskal,M Nachtnebel,R Würschum,H Krenn

doi:10.1063/5.0015397

Abstract

In situ superconducting quantum interference device magnetometry provides insights into the electrochemical dealloying mechanism of a CoPd alloy. Charge-dependent measurements of magnetic moment allow the separation of primary and secondary dealloying contributions. Coercivity evolution revealed the transition from collective ferromagnetism to superparamagnetism of small alloy clusters evolving in the dealloying process, which is interpreted as an “inverse” magnetic percolation problem. Temperature-dependent magnetization curves enable a qualitative comparison of magnetic cluster size distributions in the nanoporous Pd framework, which are found to be strongly influenced by dealloying potential. The study underlines the potential of electrochemical dealloying as a promising method for the preparation of tailor-made magnetic nanostructures.

Highlights

The remarkably simple idea to obtain nanoporous metal structures by dissolving the less noble component from a binary alloy was already discovered back in the 1970s
Coercivity evolution revealed the transition from collective ferromagnetism to superparamagnetism of small alloy clusters evolving in the dealloying process, which is interpreted as an “inverse” magnetic percolation problem
We show that the magnetic cluster size distributions can be qualitatively compared on the basis of magnetization measurements for samples dealloyed at different applied voltages

Summary

Introduction

The remarkably simple idea to obtain nanoporous metal structures by dissolving the less noble component from a binary alloy was already discovered back in the 1970s. Magnetic properties of dealloyed structures have been investigated early on, but only very recently the potential of electrochemical dealloying as a method for the preparation of nanostructured superparamagnetic materials has been recognized.. Small residues of the less noble component buried under the noble metal surface are a peculiarity of the dealloying synthesis route and a direct result of the surface diffusion mechanism, which is the key to pore formation.. Small residues of the less noble component buried under the noble metal surface are a peculiarity of the dealloying synthesis route and a direct result of the surface diffusion mechanism, which is the key to pore formation.1,14 These “impurities” need not necessarily be disadvantageous compared to pure noble-metal nanoporous structures synthesized from other techniques, but may, on the contrary, offer distinct advantages for catalysis and magnetic functionalization.. A CoPd alloy was the model system of choice for the present work, which was successively converted into nanoporous Pd with Co residues [npPd(Co)] upon electrochemical dealloying

Results

Discussion

Conclusion