Abnormal magnetoresistance inε−(Mn1−xFex)3.25Geantiferromagnets

Abstract

The magnetic, transport and magnetotransport properties of antiferromagnetic epsilon-(Mn(1-x)Fe(x))(3.25)Ge (x=0.17 and 0.2) compounds are investigated systematically. For both compounds, a large positive magnetoresistance (MR) is observed in the temperature regime below the temperature (T(t)) for a transition from a triangular to a collinear antiferromagnetic spin configuration, while a negative magnetoresistance appears between T(t) and the Neel temperature T(N), and then the MR ratio turns to be positive again above T(N). Below T(t), the positive MR reaches a maximum ratio of 6.1% at 5 K at an applied magnetic field of 5 T for the epsilon-(Mn(0.83)Fe(0.17))(3.25)Ge compound. For the epsilon-(Mn(0.83)Fe(0.2))(3.25)Ge compound, the positive MR ratio reaches its maximum at 120 K and nearly vanishes at 5 K. The origin of the anomalous positive and negative MR effects is discussed in terms of the shrinkage of the orbits, the spin fluctuations, the spin configurations, and the magnetic transitions.