Anomalous Hall resistivities of single-crystal Fe16N2 and Fe–N martensite films epitaxially grown by molecular beam epitaxy

Abstract

The anomalous and ordinary Hall resistivities for Fe16N2 (saturation magnetization 4πMs: 29 kG at room temperature) and Fe–N martensite (24.8 kG) films have been measured in the temperature range from 30 to 300 K and compared with pure Fe (21 kG) films. All films were epitaxially grown on GaAs(001) substrates by molecular beam epitaxy. The saturation anomalous Hall resistivity ρAS for Fe16N2 at 300 K was 4.0×10−7 V cm/A which was much higher than the values for Fe–N martensite (1.9×10−7 V cm/A) and Fe (1.5×10−7 V cm/A). Also the anomalous Hall constant RA at 300 K for Fe16N2 was 1.5×10−11 V cm/A G, which was much higher than the values for Fe–N martensite (0.8×10−11 V cm/A G) and Fe (0.7×10−11 V cm/A G). Such results are consistent with a much larger magnetic moment for Fe16N2. To investigate the consequences of the giant magnetic moment for Fe16N2 as compared with Fe–N martensite and Fe, the temperature dependences of ρAS and RA were measured. The values of ρAS and RA decreased monotonically with decreasing temperature for Fe16N2, Fe–N martensite and Fe. In the temperature range from 30 to 300 K, the ρAS value for Fe16N2 was much higher than the values for Fe–N martensite and Fe. This originated from the larger thermal fluctuation of the magnetization for Fe16N2. The striking features of Fe16N2 magnetism were its giant magnetic moment and its large thermal fluctuation of the magnetic moment. The electrical resistivity at room temperature for Fe16N2 was around 30 μΩ cm as compared with 10 μΩ cm for Fe. The difference was due mainly to the difference in the residual resistivities. The electrical resistivity for Fe16N2 decreased monotonically with decreasing temperature, which is normal for a metallic material.