Negative magnetoresistance in different nitrogen content EuNbO3−xNx single-crystalline thin films

Abstract

Perovskite-type europium niobium oxynitride (EuNbO₂N) exhibits colossal negative magnetoresistance (MR > –99%) at low temperatures. To investigate the role of nitrogen in the negative MR, we fabricated EuNbO_3−xN_x single-crystalline thin films with different nitrogen contents (x = 0.6, 0.7, and 1.0) and measured their magneto-transport properties. All the thin films showed a saturated magnetization of ∼3.0 μ_B f.u.⁻¹, indicating that almost half of the Eu ions existed in trivalent oxidation states, independent of x. The transport properties of the EuNbO_3−xN_x thin films gradually changed from metallic to semiconducting as x increased. The semiconducting behaviour was best explained by three-dimensional variable-range hopping conduction, suggesting that carrier localization occurred because of the random distribution of nitrogen at anion sites. As x increased, the negative MR ratio at 2 K increased up to 98%, which was in good agreement with that reported for bulk EuNbO₂N. This proved that the colossal MR of EuNbO₂N had an intrinsic origin. We speculated that the d–f exchange interaction between the localized Nb 4d¹ and Eu²⁺ 4f electrons was a key factor in the colossal negative MR of EuNbO_3−xN_x.