Micro-SQUIDs

A number of lanthanide SMMs have been studied by Wernsdorfer using the micro-SQUID technique for which the technical details can be found elsewhere... 

This chapter introduces the basic concepts that are needed to understand the quantum phenomena observed in molecular nanomagnets. All tunneling studies presented here were performed by magnetization measurements on single crystals using an array of micro-SQUIDs [4]. 

In this section we report the first study of the micro-SQUID response of a low-spin molecular system, V15, to electromagnetic radiation. The advantages of our micro-SQUID technique in respect to pulsed electron paramagnetic resonance (EPR) techniques consist in the possibility to perform time-resolved experiments (below 1 ns) [59] on submicrometer sizes samples (about 1000 spins) [22] at low temperature (below 100 mK). Our first results on Vi5 open the way for time-resolved observations of quantum superposition of spin-up and spin-down states in SMMs. Other results obtained in similar systems but with large spins concern for example EPR measurements [10], resonant photon-assisted tunneling in a Feg SMM [60]. 

The study of these systems have become possible thanks to the development of various preparation routes, from sophisticated routes for the preparation of model materials with controlled nanostructures to industrial routes for the production of large quantity of materials. It has benefited as well from the development of new experimental techniques, allowing the properties of matter to be quantitatively examined at the nanometre scale. These include Hall micro-probe [3] or micro-SQUID magnetometry [4], XMCD at synchrotron radiation facilities [5] and scanning probe microscopes [6]. This is not the topic of this chapter to describe in detail these various techniques. They are only quoted in the following sections. The reader may find in the associated references the detailed technical descriptions that he may need. 

Figure 68. Sweep rate-dependent micro-SQUID magnetization scans collected for [(triphos) Re (CN)3]4[Mn Cl]4 at 0.5 K showing hysteretic behavior. The outermost curve corresponds to a scan rate of0.560 T/s, and the scan rate decreases for each successive curve by a factor of 2, reaching the value of 0.008 T/s for the innermost curve. [Adapted from (214)].

Figure 9.22 The structure of [Fe2Ho2(OH)2(teaH)2(02CPh)4(N03)2]-6CH3CN and its hysteresis loops measured in micro-SQUID [110]. (Reprinted from Polyhedron, 25, M. Murugesu, et al., Mixed 3d/4d and 3d/4f metal clusters tetranuclear image and image complexes, and the first Fe/4f single-molecule magnets, 613-625, 2006, with permission from Elsevier.)...

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