Magnetoresistance and Field-Induced Phase Transitions in the Helical Antiferromagnetic State of Dysprosium

Field-induced magnetic phase transitions in the helical phase of dysprosium have been studied through basal-plane magnetoresistance measurements. Certain details of the measurement technique were found to be of profound importance: it is essential that the sample's internal magnetic field have high homogeneity, and that the single-crystal specimen be mounted in such a way that it may distort freely under the influence of thermal and magnetostrictive stresses. Throughout this investigation, the magnetic field was applied in the basal plane. Anomalies in the magnetoresistance, which are correlated with the field which collapses the helix at a critical value $H_c$, have been observed. For temperatures greater than 130 °K, and fields greater than $H_c$, anomalies have been observed which are believed to result from transitions from fan to ferromagnetic ordering. Resistance deviations as large as 4% were observed at 20 kOe, and important to the interpretation of microwave-absorption measurements.