Piezomagnetic behaviour in α-Fe₂O₃ nanofilms grown within nanochannels of Na-4 mica

Abstract

α-Fe₂O₃ nanofilms were grown within the 0.6 nm width nanochannels of sodium fluorophlogopite mica (Na-4 mica) structure. Due to a large difference in the values of thermal expansion coefficients of Na-4 mica and α-Fe₂O₃ a huge compressive stress was generated on the latter as the composite was cooled from 1023 K to 300 K. Magnetization measurements on the composite as a function of temperature showed the presence of piezomagnetic effect in α-Fe₂O₃. The values of piezomagnetic coefficient were estimated to be in the range 2.3×10⁻⁶ to 3.4×10⁻⁴(emu/g)/(kg/cm₂). This is of the same order as that reported earlier by work carried out on single crystals of macrodimensions. Magnetization measurements of α-Fe₂O₃ particles of diameter ~130 nm on the other hand, showed the usual behaviour viz., a magnetic phase transition from antiferromagnetic to ferromagnetic state at 237 K.