One-dimensonal Heisenberg antiferromagnet is the only solid-state system, for which the precise analytical description has been derived; it orders magnetically at 0 K. Here we propose to study AgFBF4, which consists one-dimensional AgF+ chains, and which - according to the previous experiments as well as rigorous theoretical calculations - should exhibit the following unusual characteristics:1. the intra-chain magnetic interactions should be the strongest ever measuredand simultaneously2. the anisotropy of magnetic interactions should be the largest ever observed, rendering this system a model 1D material.The purpose of this project is to determine the value of the Neel point as well as of the order parameter of AgFBF4; according to our previous measurements at ISIS the Neel point must be lower than 0.3 K.