Suppressed magnetization at the surfaces and interfaces of ferromagnetic metallicmanganites

Abstract

What happens to ferromagnetism at the surfaces and interfaces of manganites? With thecompetition between charge, spin, and orbital degrees of freedom, it is not surprising thatthe surface behaviour may be profoundly different to that of the bulk. Usinga powerful combination of two surface probes, tunnelling and polarized x-rayinteractions, this paper reviews our work on the nature of the electronic andmagnetic states at manganite surfaces and interfaces. The general observation is thatferromagnetism is not the lowest energy state at the surface or interface, which resultsin a suppression or even loss of ferromagnetic order at the surface. Two caseswill be discussed ranging from the surface of the quasi-2D bilayer manganite(La2−2xSr1+2xMn2O7) to the 3Dperovskite (La2/3Sr1/3MnO3)/SrTiO3 interface. For the bilayer manganite, which is ferromagnetic and conductingin the bulk, these probes present clear evidence for an intrinsic insulatingnon-ferromagnetic surface layer atop adjacent subsurface layers that display thefull bulk magnetization. This abrupt intrinsic magnetic interface is attributed tothe weak inter-bilayer coupling native to these quasi-two-dimensional materials.This is in marked contrast to the situation for the non-layered manganite system(La2/3Sr1/3MnO3/SrTiO3), whose magnetization near the interface is less than half the bulk value at lowtemperatures and decreases with increasing temperature at a faster rate than that for thebulk.