Intrinsic magnetic order in Cs2AgF4 detected by muon-spin relaxation

We present the results of a muon-spin relaxation study of the high-Tc analog material Cs2AgF4. We find unambiguous evidence for magnetic order, intrinsic to the material, below TC=13.95(3) K. The ratio of interplane to intraplane coupling is estimated to be |J[prime]/J|=1.9102, while fits of the temperature dependence of the order parameter reveal a critical exponent beta=0.292(3), implying an intermediate character between pure two- and three-dimensional magnetism in the critical regime. Above TC we observe a signal characteristic of dipolar interactions due to linear F-+-F bonds, allowing the muon stopping sites in this compound to be characterized.