G Allan, W M Lomer, R D Lowde and C G Windsor, Susceptibility and Intra-Atomic Exchange in Nickel, Phys. Rev. Letters 20, 933-936, 1968.

In the years 1965 to 1970, Windsor worked with Ray Lowde on the PLUTO reactor "chopper", a time of flight inelastic spectrometer. It's speciality, which Windsor made his own, was to measure the complete scattering function S(Q,hw ) as a function of the scattering vector Q, and energy transfer hw the generalised susceptibility in magnet materials. His experiments on paramagnetic nickel enabled this function to be measured in an itinerant magnet for the first time. But the results needed a theory to extract the key information on the Hamiltonian of itinerant magnets. With the help of a French student, Guy Allen, Windsor was able to fit to experiment the response from a tight binding model of nickel and so determine the Hubbard exchange interaction Ieff(Q). The field has continued with measurements and calculations over ever wider temperature and energy ranges.