Non-magnetic materials can be magnetically doped in high concentrations in a highly controlled way

Nanotechnologists from the University of Twente’s MESA+ and MIRA research institutes have developed a method for incorporating magnetic elements into non-magnetic materials in a highly controlled way. Using this technique, it is possible to drastically change the electrical behaviour of metals and even to give semiconductors magnetic properties.

University of Twente researchers were able to incorporate magnetic elements into a non-magnetic layer of gold in a highly controlled manner. They did so by coating the gold layer with a single layer of organic molecules, each containing a single metal ion: some containing cobalt and some containing zinc. The cobalt ions have an unpaired electron spin and therefore behave as an elementary magnet, while zinc ions do not have magnetic properties. By adjusting the relative concentration of cobalt and zinc ions, it is possible to fine tune the magnetic properties of the final material. Molecular self-assembly causes the metal compounds to spread homogenously over the layer of gold.

Unprecedentedly high concentrations

What makes the method so special is that it produces unprecedentedly high concentrations of magnetic “doping” without causing the magnetic elements to cluster. In the methods used to date, it was very difficult to spread the magnetic elements homogenously over the final material, particularly at high concentrations.

It is possible to create materials with completely new properties. This paves the way for semi-conductors with magnetic properties: one of the holy grails of physics. Semi-conductors of this kind could be used for both memory storage (magnetic) and data processing (electrical) in a new generation of computers

Nature Nanotechnology – Tunable doping of a metal with molecular spins

The mutual interaction of localized magnetic moments and their interplay with itinerant conduction electrons in a solid are central to many phenomena in condensed-matter physics, including magnetic ordering and related many-body phenomena such as the Kondo effect1, the Ruderman–Kittel–Kasuya–Yoshida interaction2 and carrier-induced ferromagnetism in diluted magnetic semiconductors3. The strength and relative importance of these spin phenomena are determined by the magnitude and sign of the exchange interaction between the localized magnetic moments and also by the mean distance between them. Detailed studies of such systems require the ability to tune the mean distance between the localized magnetic moments, which is equivalent to being able to control the concentration of magnetic impurities in the host material. Here, we present a method for doping a gold film with localized magnetic moments that involves depositing a monolayer of a metal terpyridine complex onto the film. The metal ions in the complexes can be cobalt or zinc, and the concentration of magnetic impurities in the gold film can be controlled by varying the relative amounts of cobalt complexes (which carry a spin) and zinc complexes (which have zero spin). Kondo and weak localization measurements demonstrate that the magnetic impurity concentration can be systematically varied up to ~800 ppm without any sign of inter-impurity interaction. Moreover, we find no evidence for the unwanted clustering that is often produced when using alternative methods.

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