The magnetization reversal behaviour for SmCo_6.8Zr_0.2 and SmCo_6.8Zr_0.2/\alpha -(Fe,Co) nanocrystalline magnets at low temperature

This paper reports that the SmCo_6.8Zr_0.2 nanocrystalline permanent magnets and SmCo_6.8Zr_0.2/\alpha-(Fe,Co) nanocomposite permanent magnets are successfully produced by mechanical alloying and subsequently annealing at 700 ^\circC for 10 minutes. The x-ray diffraction results show that the phase structure of SmCo_6.8Zr_0.2 nanocrystalline permanent magnets is composed of SmCo₇ phase and SmCo_6.8Zr_0.2/\alpha-(Fe, Co) nanocomposite permanent magnets is composed of SmCo₇ and \alpha -(Fe,Co) phases. The mechanism of magnetization reversal is mainly controlled by inhomogeneous domain wall pinning in SmCo_6.8Zr_0.2 and SmCo_6.8Zr_0.2/\alpha-(Fe,Co) magnets. The inter-grain exchange interaction at low temperature is investigated, which shows that the inter-grain exchange interaction of SmCo_6.8Zr_0.2/\alpha-(Fe,Co) magnets increases greatly by the decrease of the measured temperature. According to \Delta m_\rm irr-H/H_\rm cj, \Delta m_\rm rev-H/H_\rm cj and \chi_\rm irr-H/H_\rm cj curves at room temperature and 100 K, the changes of irreversible and reversible magnetization behaviours of SmCo_6.8Zr_0.2 and SmCo_6.8Zr_0.2/\alpha-(Fe,Co) magnets with the decreasing temperature are analysed in detail. The magnetic viscosity and the activation volume of SmCo_6.8Zr_0.2 and SmCo_6.8Zr_0.2/\alpha-(Fe,Co) magnets at different temperatures are also studied.