Magnetic X-Ray Dichroism Study of the Nearest-Neighbor Spin-Spin Correlation Function and Long-Range Magnetic Order Parameter in Antiferromagnetic NiO

A new effect on the X-ray absorption line shape is described which is proportional to the nearest-neighbor spin-spin correlation function. We present theory and demonstrate the use of linear polarized x-ray absorption spectroscopy to study the temperature dependence of the long-range order parameter and the nearest-neighbor spin-spin correlation function in antiferro-magnetic NiO.