Radiation detection with the pyromagnetic effect

The dynamic pyromagnetic response of several materials with magnetic phase transitions near 300°K has been measured by a method initially described by Chynoweth [1]. The results indicate that practical broad-band pyromagnetic radiation detectors operating in a fast dynamic thermal mode are possible. The best results were obtained with gadolinium and manganese germanide crystals which have second-order magnetic phase transitions slightly below 300°K. Their responses peaked at 300°K, but remained high over fairly large temperature ranges, a 25°C interval in the case of gadolinium. The NEP of ∼ 10^-8W.Hz^-1/2(0.12 cm²active area) obtained with gadolinium is larger by a factor of 10 than that reported for 300°K pyroelectric detectors, but was limited by laboratory noise pickup in the detector coil rather than the internal Johnson noise. Improved techniques should result in lower NEPs. The pyromagnetic responses at the critical temperatures of two materials with first-order magnetic phase transitions, FeRh and MnAs, were considerably smaller than expected. They were also anomalously discontinuous compared with the measured step in the static magnetization. A third material, Fe.71Mn1.44As, with a first-order transition at 344°K, gave a much larger response, but over a very narrow temperature range.