Modification of Electrical and Magnetic Properties of Fe₃O₄ Epitaxial Thin Films by Nitrogen Substitution for Oxygen

Abstract

Epitaxial thin films of nitrogen-substituted Fe 3 O 4 (Fe 3 O 4−y N y ) were synthesized on MgO (001) substrates by using nitrogen-plasma-assisted pulsed laser deposition. The obtained Fe 3 O 4−y N y thin films showed ferrimagnetic behavior at room temperature. The carrier density of the films was decreased by nitrogen substitution up to y = 0.4. These properties were similar to those of A-site (tetrahedral site)-substituted Fe 3 O 4 , such as Zn x Fe 3−x O 4 or Mn x Fe 3−x O 4 , previously reported. On the other hand, the electrical resistivity of the Fe 3 O 4−y N y thin films at room temperature was rather insensitive to y, in sharp contrast to Zn x Fe 3−x O 4 or Mn x Fe 3−x O 4 , of which the resistivity drastically increased with increase of x. These results indicated that nitrogen substitution is an effective method to control the carrier density of Fe 3 O 4 without disturbing the carrier conduction through the B-site (octahedral site) Fe ion network. Density functional theory-based first-principles calculation predicted that Fe 3 O 4−y N y is half-metallic.

Exploring Metastable Oxynitrides by Thin Film Growth Approach

“…Recently, applications of Fe3O4 for spintronics devices such as magnetic tunneling junctions [ 38 , 39 ] attract attention due to its half metallicity as well as ferrimagnetism with Néel temperature of ~860 K. While the effect of cation substitution on the physical properties of Fe3O4 was investigated [ 40 , 41 ], few attempts have been made to control them via anion substitution due to the thermal instability of anion doped Fe3O4. Epitaxial thin films of inverse spinel-type Fe3O4−yNy (0 ≤ y ≤ 0.4) were grown on MgO (100) substrates at 300 °C by using NPA-PLD [ 35 ]. The Fe3O4−yNy films were ferrimagnetic at room temperature.…”

“…(left) Crystal structure of a cation (Mn or Zn) or N doped Fe3O4 thin film and (right) electrical resistivities of Fe3−xMxO4 (M=Mn or Zn) and Fe3O4−yNy at room temperature.Reproduced from ref 35. with permission of American Chemical Society.…”