Reentrant spin glass behavior in layered manganite La1.2Sr1.8Mn2O7 single crystals

We report a detailed study of ac/dc magnetization and longitudinal/transver se transport properties of La1.2Sr1.8Mn2O7 single crystals below T-c=118 K. We find that the resistivity minimum at 40 K is related to the reentrant s pin glass phase at the same temperature, accompanied by additional anomalou s Hall effects. The carrier concentration from the ordinary Hall effects re mains constant during the transition and is close to the nominal doping lev el (0.4 holes/Mn). The spin glass behavior comes from the competition betwe en ferromagnetic double exchange and antiferromagnetic superexchange intera ctions, which leads to phase separation, i.e., a mixture of ferromagnetic a nd antiferromagnetic clusters, representing the canted antiferromagnetic st ate. (C) 2001 American Institute of Physics.