PHOTOPYROELECTRIC DETECTION OF MAGNETIC PHASE-TRANSITIONS - APPLICATION TO FERROMAGNETIC AND ITINERANT ELECTRON ANTIFERROMAGNETIC MATERIALS

It is demonstrated for the first time theoretically and experimentally that the photopyroelectric (PPE) method with front excitation and rear detection, is suitable for the investigation of magnetic phase transitions. Accurate plots of the PPE voltage amplitude for Ni(100-x)Cu(x) (x = 28, 30, 33%) alloys were obtained in the critical region with a signal-to-noise (S/N) ratio better than 10(2). By increasing the modulation frequency of the radiation, the discontinuity of the PPE signal for the same specific heat anomaly is enhanced, as the thermally thin sample becomes thermally thick. The Curie temperatures determined by this method are close to those obtained by magnetic measurements. The itinerant electron antiferromagnetism-to-Pauli paramagnetism phase transition was also detected in chromium and the alloy gamma-(Fe55Mn45)80Rh20, and the possible phase transition of alpha-titanium was investigated by this method. No anomaly in the PPE signal for alpha-Ti was found up to a S/N ratio of 10(2).