A neutron diffraction determination of the critical exponent β for the n = 4 system holmium

The temperature dependence of the order parameter associated with the magnetic phase transition in Ho near 131 K has been measured by neutron diffraction. The results show a power law behaviour for the order parameter with an exponent of β = 0.39 (+ 0.04, - 0.03) for the reduced temperature range 0.007 <= epsilon <= 0.3. This value is in agreement with recent predictions for an n = 4 vector model studied in the renormalization group technique. (author)