Highly amplitude-sensitive photonic-crystal-fiber-based plasmonic sensor

Abstract

The low-temperature magnetic properties of the many pyrrhotite varieties have not beenstudied extensively. Monoclinic pyrrhotite (Fe7S8) goes through the Besnus transition at ~30–34 K, which isused widely to diagnose its presence in bulk samples. Other pyrrhotite polytypes are assumed to beantiferromagnetic, although it has been suggested occasionally that some may also haveremanence-carrying capabilities. Here we compare the magnetic properties of monoclinic (4M) andhexagonal (3T) pyrrhotite at low temperatures. The 4M pyrrhotite records a Besnus transition consistently.Despite not recording a Besnus transition, 3T pyrrhotite has a magnetic remanence at room temperature andhas distinctive room- and low-temperature magnetic properties that cannot be explained by known orunidentified impurities (with abundances<0.1%). Some 3T-pyrrhotite samples have exceptionally high(>700 mT) and stable coercivities below 50 K. The importance of this mineral in fossil or active gas hydrateand methane venting environments makes it important to develop a more detailed understanding of itsoccurrences and magnetic properties.