Poster Presentation 23rd International Society of Magnetic Resonance Conference 2023

Zero-field nmr of bornite (Cu5FeS4) (#321)

Thai C.L. Ly 1 , Richard Yong 1 , David G. Miljak 1
  1. CSIRO, Lucas Heights, NSW, Australia

Abstract

The first reported 63Cu zero-field nuclear magnetic resonance (ZFNMR) spectra of an industrially significant copper mineral, bornite (Cu5FeS4) is presented here. The motivation for the detection of bornite stems from expanding the quantitative measurement of key copper mineral species amenable to ZFNMR for industrial magnetic resonance (MR) sensors [1]. Such industrial sensors have the capability to provide real-time mineral measurements for mining applications such as characterisation and sorting.

            Observation of bornite by ZFNMR has not been reported prior to this research however, the following mineral characteristics suggested bornite was detectable via magnetic resonance. Firstly, bornite has anti-ferromagnetic ordering below the Néel temperature of ~70 K [2], which implies zero-field resonances due to possible transferred hyperfine field onto copper nuclei.  In addition to this, a superstructure has been reported in bornite with some copper sites without cubic symmetry and thus imply the existence of quadrupolar resonances [3]. Yet, characteristics such as hyperfine field strength and nuclei ordering were not in agreement in literature and further hindered the ZFNMR search for bornite.       

Zero-field resonances were observed in two natural bornite samples at 10 K with a bespoke, home-built cryogenic probe that was housed in a JANIS cryostat. Broad resonance lines were detected between 8 – 22 MHz however, the frequencies, relative peak heights and linewidths were not in agreement between the two samples which may be due to possible non-stoichiometry [4], copper/iron ordering [5] and unresolvable crystallographic characteristics. With large differences between both spectra, no definitive conclusions about the crystal structure or magnetic properties could be deduced. However, the spectra imply the existence of a superstructure with possible magnetic ordering. Attempts to track the resonances with increasing temperature were unsuccessful. The spread of resonances and short decay times observed at 10 K indicate unfavourable conditions for the observation of resonances above 10 K.

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