Collective magnetic response of inhomogeneous nanoisland FeNi films around the percolation transition

TL;DR

This study investigates the complex magnetic responses of inhomogeneous nanoisland FeNi films near the percolation transition, revealing anomalous out-of-plane paramagnetic-like behavior and in-plane diamagnetic responses influenced by interface effects.

Contribution

It uncovers the anomalous magnetic behavior of nanoisland FeNi films around the percolation threshold, highlighting the role of interface interactions and localized electron orbital moments.

Findings

Out-of-plane magnetization remains unsaturated and paramagnetic-like at high fields.

Anomalous magnetization response varies with film thickness, peaking near 1.1 nm.

In-plane response saturates above 1.5-2 T, showing diamagnetic-like behavior.

Abstract

By using superconducting quantum interference device (SQUID) magnetometry we investigated anisotropic high-field (H < 7 T) low-temperature (10 K) magnetization response of inhomogeneous nanoisland FeNi films grown by rf sputtering deposition on Sitall (TiO2) glass substrates. In the grown FeNi films, the FeNi layer nominal thickness varied from 0.6 to 2.5 nm, across the percolation transition at the d_c=1.8 nm. We discovered that, beyond conventional spin-magnetism of Fe21Ni79 permalloy, the extracted out-of-plane magnetization response of the nanoisland FeNi films is not saturated in the range of investigated magnetic fields and exhibits paramagnetic-like behavior. We found that the anomalous out-of-plane magnetization response exhibits an escalating slope with increase in the nominal film thickness from 0.6 to 1.1 nm, however, it decreases with further increase in the film thickness, and then practically vanishes on approaching the FeNi film percolation threshold. At the same time, the in-plane response demonstrates saturation behavior above 1.5-2 T, competing with anomalously large diamagnetic-like response, which becomes pronounced at high magnetic fields. It is possible that the supported-metal interaction leads to the creation of a thin charge-transfer (CT) layer and a Schottky barrier at the FeNi film/Sitall (TiO2) interface. Then, in the system with nanoscale circular domains, the observed anomalous paramagnetic-like magnetization response can be associated with a large orbital moment of the localized electrons. The observed magnetization response is determined by the interplay between the paramagnetic- and diamagnetic-like contributions.