Comment on ``Spin Dependent Hopping and Colossal Negative Magnetoresistance in Epitaxial $Nd_{0.52}Sr_{0.48}MnO_{3}$ Films in Fields up to 50 T''

TL;DR

This paper critiques Wagner et al.'s modification of Mott's model for magnetoresistance in manganite films, proposing an alternative explanation that better accounts for observed scaling behaviors in ferromagnetic and paramagnetic states.

Contribution

The authors present a different modification to Mott's hopping model that more accurately explains the negative magnetoresistance scaling observed in manganite films.

Findings

Their model explains the observed scaling behavior in both ferromagnetic and paramagnetic regimes.

The proposed modification better fits experimental data than Wagner et al.'s model.

The paper clarifies the role of spin misorientation in hopping conduction mechanisms.

Abstract

Recently Wagner et al. [Phys. Rev. Lett. Vol. 81, P. 3980 (1998)] proposed that Mott's original model be modified to incorporate a hopping barrier which depends on the misorientation between the spins of electrons at the initial and the final states in an elementary process. They further claimed that using the model they can explain the observed scaling behavior-- negative-magnetoresistivity scaling proportional to the Brillouin function $\cal{B}$ in the ferromagnetic state and to ${\cal{B}}^2$ in the paramagnetic state. In this comment we argue that the modification needed for Mott's original model is different from that proposed by Wagner et al. and further show that our picture will successfully explain the observed scaling in the two regimes.