Small polaron transport and glassy ferromagnetism in (LaSr)Co1−xFexO4
Akira Tabuchia, Hirofumi Kawanakab, , , Hiroshi Bandob, Toku Sasakia and Yoshikazu Nishiharaa
aFaculty of Science, Ibaraki University, Mito 310-8512, Japan bNational Institute of Advanced Industrial Science and Technology, Tsukuba 305-8568, Japan
Received 8 December 2005; accepted 12 December 2005. Available online 10 February 2006.
Abstract
We have studied transport and magnetic properties of (LaSr)Co1−xFexO4 system. The conduction of (LaSr)CoO4 is three-dimensional variable range hopping at low temperatures below 300 K and is expected to be thermally activated hopping above 900 K. With increasing x the electronic conduction changes from a variable range hopping type to a band-gap type between x = 0.2 and 0.6. Substitution of Co by Fe induces ferromagnetism with large hysteresis in the temperature dependence of magnetization below the transition temperature. This glassy ferromagnetism appears in the concentration region where the variable range hopping of small polaron is dominant. In the samples with x ≥ 0.6 the temperature dependence of magnetization shows an antiferromagnetic behavior. The lattice parameters a and c increase with increasing x. However, the increasing rate of c-axis is small in the variable hopping region below x 0.2. The values of resistivity and ferromagnetic moment become maximum around x = 0.2. The transport and magnetic properties have a close correlation in this system.
Keywords: Small polaron; Glassy ferromagnetism; (LaSr)Co1−xFexO4
300 K and is expected to be thermally activated hopping above 
