Magnetoresistance in Helical Antiferromagnet Eu Metal Thin Films

Europium (Eu) metal has a body centered cubic crystal structure which, upon a paramagnetic-to-helical magnetic transition, undergoes a body centered tetragonal distortion. The magnetic helix appears below Néel temperature (T_N) of ~90 K, and the presence of a magnetic field gives rise to conical helimagnet. We have prepared Eu metal thin films on Si (001) substrates using Eu metal as a target by pulsed laser deposition (PLD). The transport measurement shows the helical antiferromagnetic transition at 88 K, and a thermal hysteresis reveals the first-order nature of the phase transition. We present the magnetoresistance (MR) of Eu thin films when the magnetic field (B) is applied both out-of-plane and in-plane. We found, at temperatures below T_N, the MR is positive whereas above T_N the MR is negative. We also observed the hysteretic oscillation above 30 K and below the Néel temperature. The hysteretic oscillations observed in the MR is believed to be associated with the change in the distribution of the antiferromagnetic domains in Eu caused by the interplay of the applied magnetic field and the strain in the films.