We measured dilute Gd1-xYx single crystals (x < 0.1) samples using an a.c. magnetoresistance technique. This technique consists in applying a constant current to the sample and measuring the temperature dependent a.c. voltage under a time modulated external magnetic field (f = 333 Hz). The a.c. voltage signal is decomposed in real and imaginary components or, alternatively, in amplitude and phase signals relative to the a.c. magnetic field. This technique proved to be extremely sensitive and effective to display all the magnetic phase transitions revealed by the previous d.c. transport measurements, plus an additional spectrum of other critical features.