Phase coexistence and exchange-bias effect in LiMn2O4 nanorods

In this paper, the magnetic properties of LiMn2O4 nanorods with an average diameter of ∼100nm and length of ∼1μm are investigated. The temperature dependences of dc and ac susceptibility measurements show that LiMn2O4 nanorods experience multiple magnetic phase transitions upon cooling, i.e., paramagnetic (PM), antiferromagnetic (AFM), canted antiferromagnetic (CAFM), and cluster spin glass (SG). The coexistence between a long-range ordered AFM phase due to a Mn4+−Mn4+ interaction and a cluster SG phase originating from frozen AFM clusters at low temperature in LiMn2O4 nanorods is elucidated. Field-cooled hysteresis loops (FC loops) and magnetic training effect (TE) measurements confirm the presence of an exchange-bias (EB) effect in LiMn2O4 nanorods below the Néel temperature (TN∼60K). Furthermore, by analyzing the TE, we conclude that the observed EB effect originates completely from an exchange coupling interaction at the interface between the AFM and cluster SG states. A phenomenological model based on phase coexistence is proposed to interpret the origin of the EB effect below 60 K in the present compound. In turn, the appearance of the EB effect further supports the coexistence of AFM order along with a cluster SG state in LiMn2O4 nanorods.