Showing papers by "J. S. Gardner published in 2001"

Electron spin resonance above T{sub}c in layered manganites.

Abstract: We have performed electron spin resonance (ESR) and dc magnetization measurements on single crystals of La{sub 2(1-x)}Sr{sub 1+2x}Mn{sub 2}O{sub 7} up to 800 K with special emphasis on the x=0.4 composition. The ESR linewidth shows behavior similar to that observed in the three-dimensional perovskites and above -500 K can be described by a universal expression {Delta}H{sub pp}(T)=[C/T{sub x}(T)]{Delta}H{sub pp}({sup {infinity}}). The linewidth and the resonance field become anisotropic below -500 K. The anisotropy in the resonance field is proportional to the magnetization M, and we concluded that it is intrinsic to the system. We show that demagnetization effects can explain only part of the anisotropy. The remainder arises from short-range uniaxial terms in the Hamiltonian that are associated with the crystal field and Dzialozhinsky-Moriya interactions. The anisotropy in the linewidth is attributed to the easy-plane ferromagnetic ordering, which also arises from the short-range anisotropy.