Behavioral response of pyrite structured Co0.2Fe0.8S2 nano-wires under high-pressure up to 8 GPa – Mössbauer spectroscopic and electrical resistivity studies

Abstract

Pyrite-structured Co0.2Fe0.8S2 nano wires with aspect ratio 45:1, synthesized using solution colloid method were studied under high pressure up to 8GPa using 57Fe Mössbauer spectroscopy (using diamond anvil cell) and electrical resistivity (using tungsten carbide cell) techniques. Room temperature S K-edge XANES studies at INFN-LNF synchrotron beam line signified the changes in the electronic structure owing to Co substitution. Magnetic measurements at 5K demonstrated disordered ferromagnetic behavior similar to Griffith phase. The value of isomer shift identified Fe in divalent, low spin state corresponding to pyrite structure. Higher value of quadrupole splitting observed at ambient condition was due to large lattice strain and electric field gradient generated by large surface to volume ratio of the nano size of the system. With applied pressure, the value followed the expected trend of increase up to 4.3GPa, then to decrease till 6.4GPa. Such change in the trend suggested a phase transition. On decompression to ambient pressure, the system seemed to retain high pressure phase and nano structure. The pressure coefficient of electrical resistivity varying from −0.0454 to −0.166Ω-cm/GPa across the transition pressure of ~4.5GPa was sluggish suggesting second order phase transition. The pressure-dependent variations by Mössbauer parameters and electrical resistivity showed identical result. This is the first report of pressure effect on nano sized Co0.2Fe0.8S2. Effect of particle size on transition pressure could not be evaluated due to lack of available reports on bulk system.