Nanocrystallization and Amorphization Induced by Reactive Nitrogen Sputtering in Iron and Permalloy

TL;DR

This study investigates how reactive nitrogen sputtering induces nanocrystallization and amorphization in iron and permalloy thin films, revealing the effects of nitrogen partial pressure on their structure and magnetic properties.

Contribution

It provides new insights into how varying nitrogen partial pressure during sputtering controls the nanostructure and magnetic properties of Fe and NiFe thin films.

Findings

Lower nitrogen pressures produce nanocrystalline structures.

Higher nitrogen pressures lead to amorphous structures.

Magnetic properties of FeN improve with nanocrystallization.

Abstract

Thin films of iron and permalloy Ni80Fe20 were prepared using an Ar+N2 mixture with magnetron sputtering technique at ambient temperature. The nitrogen partial pressure, during sputtering process was varied in the range of 0 to 100%, keeping the total gas flow at constant. At lower nitrogen pressures RN2<33% both Fe and NiFe, first form a nanocrystalline structure and an increase in nitrogen partail pressure results in formation of an amorphous structure. At intermediate nitrogen partial pressures, nitrides of Fe and NiFe were obtained while at even higher nitrogen partial pressures, nitrides themselves became nanocrystalline or amorphous. The surface, structural and magnetic properties of the deposited films were studied using x-ray reflection and diffraction, transmission electron microscopy, polarized neutron reflectivity and using a DC extraction magnetometer. The growth behavior for amorphous film was found different as compared with poly or nanocrystalline films. The soft-magnetic properties of FeN were improved on nanocrystallization while those of NiFeN were degraded. A mechanism inducing nanocrystallization and amorphization in Fe and NiFe due to reactive nitrogen sputtering is discussed in the present article.