Exploring Linear and Nonlinear AC-susceptibilities in a Single Crystal of alpha-Fe2O3 around the Morin transition using a Home-built AC Susceptometer

Abstract

A home-built AC susceptometer is designed and fabricated for the measurement of phase resolved linear and nonlinear AC susceptibilities. The set up is designed for measurements in the temperature ranging from 77K to 300K, AC magnetic field up to few Oe and frequency up to a few kHz. Apart from routine ferromagnets or antiferromagnets (AFM), complex magnetic phases such as spin glasses can be identified using higher harmonic susceptibility. Hematite, a well known spin canted system , which turns to pure antiferromagnetic phase below the Morin transition has yet not been explored through non-linear susceptibility. Temperature dependence of linear (χ1) and nonlinear susceptibilities (χ2 and χ3) in a single crystal of hematite (α −Fe2O3) have been investigated around the Morin transition. Here the Morin transition which demarcates pure AFM from the spin-canted phase is observed in χ1. Furthermore, the transition is also clearly traced in higher harmonic susceptibilities. Here, the crossover in χ3 (which signifies magnetic transition pertaining to Morin) is measured for the first time, to the best of our knowledge. In addition, signatures of a double transition are observed in susceptibility (χ1, χ2, χ3), in the single crystal , ruling out size effects. We also observe signatures of χ2, in the absence of externally applied DC field.