Hall magnetometry

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. 

Many novel experiments based on this technique have been reported in the literature (e.g., Abulafia et al. 1995, 1996, Yeshurun et al. 1996, Doyle et al. 1997). For the purpose of this section, I wish to concentrate on two results, which are shown in fig. 9 (Werner 1997). First, the flux profile (fig. 9a) obtained at a certain external field ( 280 mT, 60 K) again shows all the characteristic Bean-like features and a (smeared-out) increase of the field at the sample edge as expected from demagnetisation. Second, the comparison between the local Hall-probe measurement and SQUID magnetometry (fig. 9b) is as favourable as in the case of torque magnetometry, i.e., the current densities deduced... 

Fig. 9. (a) Measurement of the flux profile in a single crystal with a multi-Hall-probe array versus sensor position (Werner 1997). (b) Comparison of experimental data obtained by SQUID and Hall probe magnetometry... 

Wu et al. (1993) have studied the canting model in more detail and have given both the calculated and experimental data as shown in fig. 53 for Tbjc(FeCo)i t alloys with A w 1800. It is seen clearly that there is an anomalous drop near the compensation point when using torque magnetometry with the field at 45". The figure also shows the experimental data and calculated ATu curve in terms of the extraordinary Hall effect. We notice that the torque technique produces a wider and deeper apparent dip and the Hall effect techniques produce a much narrower dip for the T-dominant case and a narrow peak for the R-dominant case. 

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