Electron spin resonance above T-C in layered manganites - art. no. 174413

We have performed electron spin resonance (ESR) and de magnetization measur ements on single crystals of La2(1-x)Sr1+2xMn2O7 up to 800 K with special e mphasis on the x=0.4 composition. The ESR linewidth shows behavior similar to that observed in the three-dimensional perovskites and above similar to 500 K can be described by a universal expression DeltaH(pp)(T)=[C/T chi (T) ]DeltaH(pp)(infinity). The linewidth and the resonance field become anisotr opic below similar to 500 K. The anisotropy in the resonance field is propo rtional to the magnetization M, and we concluded that it is intrinsic to th e system. We show that demagnetization effects can explain only part of the anisotropy. The remainder arises from short-range uniaxial terms in the Ha miltonian that are associated with the crystal field and Dzialozhinsky-Mori ya interactions. The anisotropy in the linewidth is attributed to the easy- plane ferromagnetic ordering, which also arises from the short-range anisot ropy.