The physics of manganites: Structure and transport

The fundamental physical properties of doped LaMnO3, generically termed "ma nganites," and much of the underlying physics, were known more than 40 year s ago. This article first reviews progress made at that time, the concept o f double exchange in particular, and points out the missing elements that h ave led to a massive resurgence of interest in these and related materials. More recent research is then described, treating first the ground states t hat emerge as divalent atoms are substituted for trivalent La. A wide range of ground states appear, including ferromagnetic metals, orbital- and char ge-ordered antiferromagnets, and more complex stripe and spin-glass states. Because of the interest in so-called colossal magnetoresistance that occur s in the ferromagnetic/metallic composition range, a section is devoted to reviewing the atypical properties of that phase. Next the high-temperature phase is examined, in particular, evidence for the formation of self-trappe d small polarons and the importance of Jahn-Teller coupling ia this process . The transitions between the high-temperature polaronic phase and the ferr omagnetic and charge-ordered states are treated in a fourth section. In eac h section, the authors stress the competition among charge, spin, and latti ce coupling and review the current state of theoretical understanding. They conclude with some comments on the impact that research on these materials has on our understanding of doped oxides and other strongly correlated ele ctronic materials.