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 EuNbO3−xNx 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 μB f.u.−1, indicating that almost half of the Eu ions existed in trivalent oxidation states, independent of x. The transport properties of the EuNbO3−xNx 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 EuNbO3−xNx.