Magnetic Fingerprints of sub-100 nm Fe Nanodots

TL;DR

This study uses the FORC method to analyze magnetic behaviors of sub-100 nm Fe nanodots, revealing size-dependent transition from single domain to vortex states and providing detailed magnetic phase information.

Contribution

It introduces the application of FORC diagrams to characterize magnetic state transitions and vortex behaviors in nanodots of different sizes, with quantitative phase analysis.

Findings

52 nm nanodots are single domain with size-consistent coercivity.

58 and 67 nm nanodots exhibit vortex states with vortex nucleation and annihilation.

FORC diagrams reveal detailed magnetic phase fractions and transition fields.

Abstract

Sub-100 nm nanomagnets not only are technologically important, but also exhibit complex magnetization reversal behaviors as their dimensions are comparable to typical magnetic domain wall widths. Here we capture magnetic "fingerprints" of 1 billion Fe nanodots as they undergo a single domain to vortex state transition, using a first-order reversal curve (FORC) method. As the nanodot size increases from 52 nm to 67 nm, the FORC diagrams reveal striking differences, despite only subtle changes in their major hysteresis loops. The 52 nm nanodots exhibit single domain behavior and the coercivity distribution extracted from the FORC distribution agrees well with a calculation based on the measured nanodot size distribution. The 58 and 67 nm nanodots exhibit vortex states, where the nucleation and annihilation of the vortices are manifested as butterfly-like features in the FORC distribution and confirmed by micromagnetic simulations. Furthermore, the FORC method gives quantitative measures of the magnetic phase fractions, and vortex nucleation and annihilation fields.