Finite size effects with variable range exchange coupling in thin-film Pd/Fe/Pd trilayers

TL;DR

This study investigates how the magnetic properties of Pd/Fe/Pd trilayers change with varying top Pd layer thickness, revealing finite size effects and nonuniform exchange interactions that influence nanomagnetism in thin films.

Contribution

It provides new insights into finite size effects and the role of variable exchange coupling in thin-film Pd ferromagnetism, with detailed analysis of thickness-dependent magnetic properties.

Findings

Magnetization and Curie temperature decrease with thinner top Pd layers.

Coercivity increases as the top Pd layer becomes thinner.

The critical exponent approaches 0.5 with increasing Pd layer thickness.

Abstract

The magnetic properties of thin-film Pd/Fe/Pd trilayers in which an embedded ~1.5 A-thick ultrathin layer of Fe induces ferromagnetism in the surrounding Pd have been investigated. The thickness of the ferromagnetic trilayer is controlled by varying the thickness of the top Pd layer over a range from 8 A to 56 A. As the thickness of the top Pd layer decreases, or equivalently as the embedded Fe layer moves closer to the top surface, the saturated magnetization normalized to area and the Curie temperature decrease whereas the coercivity increases. These thickness-dependent observations for proximity-polarized thin-film Pd are qualitatively consistent with finite size effects that are well known for regular thin-film ferromagnets. The critical exponent $\beta$ of the order parameter (magnetization) is found to approach the mean field value of 0.5 as the thickness of the top Pd layer increases. The functional forms for the thickness dependences, which are strongly modified by the nonuniform exchange interaction in the polarized Pd, provide important new insights to understanding nanomagnetism in two-dimensions.