Spatial evolution of the ferromagnetic phase transition in an exchange graded film

TL;DR

This study combines experiments and modeling to investigate how a gradient in exchange strength affects the spatial evolution of ferromagnetic phase transition in a NiCu alloy film, revealing a controllable boundary between magnetic phases.

Contribution

It introduces a method to engineer and analyze the spatial evolution of ferromagnetic phase transitions using a gradient in exchange strength, supported by experimental validation.

Findings

The film behaves as a continuum of uncoupled ferromagnetic layers with varying Curie temperatures.

A mobile boundary between ordered and disordered regions can be controlled by temperature.

Magnetic field can reversibly control the magnetically ordered volume.

Abstract

A combination of experiments and numerical modeling was used to study the spatial evolution of the ferromagnetic phase transition in a thin film engineered to have a smooth gradient in exchange strength. Mean-field simulations predict, and experiments confirm that a 100 nm Ni[x]Cu[1-x] alloy film with Ni concentration that varies by 9 % as a function of depth behaves predominantly as if comprised of a continuum of uncoupled ferromagnetic layers with continuously varying Curie temperatures. A mobile boundary separating ordered and disordered regions emerges as temperature is increased. We demonstrate continuous control of the boundary position with temperature, and reversible control of the magnetically ordered sample volume with magnetic field.