Abstract
An improved multi-cycle low-temperature demagnetization (MC-LTD) method for multidomain (MD) Fe3O4 (magnetite) by repeating LTD cycles between any two temperatures below 300K is proposed to provide more rigorous constraints on the utilization of the LTD mechanism. MC-LTD was performed for four temperature intervals, 300–150K, 150–125K, (cycling through the isotropic point Tk∼130K, where the first magnetocrystalline anisotropy constant K1 changes sign), 125–95K (cycling through the Verwey transition Tv∼120K, where crystal symmetry changes from cubic to monoclinic) and 95–60K. Results show that the remanence loss during MC-LTD depends on the number of LTD cycles. Above Tv, demagnetization of remanence after MC-LTD is caused by the gradual reorganization of magnetic domains. For the 95–125K interval, the remanence loss results from the changes of easy axes between [001] of the cubic phase above Tv and the c-axis of the monoclinic phase below Tv. These two processes approximately follow the Boltzmann-analog relation, but the latter involves more degree of freedom. Below Tv, thermal equilibrium processes control the minor decay (less than 0.5% of the initial remanence intensity) of remanences.
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