Spontaneous Distortion and Ferromagnetism Induced by Quantum-well States in Pd(100) Ultrathin Films

TL;DR

This study investigates how quantum-well states induce ferromagnetism and structural changes in Pd(100) ultrathin films, revealing a novel inverse mechanism of Stoner's theory through combined experimental and computational analysis.

Contribution

It demonstrates that ferromagnetism in Pd ultrathin films causes lattice expansion and structural uniformity, revealing a new modulation mechanism of the density of states contrary to traditional theories.

Findings

Ferromagnetic Pd films exhibit flatter, more uniform growth.

Lattice expansion occurs in ferromagnetic Pd to reduce electron kinetic energy.

A new inverse mechanism of Stoner's theory modulating density of states was identified.

Abstract

We study the crystal structure of Pd(100) ultrathin films, which show ferromagnetism induced by the quantum confinement effect, using in-situ X-ray crystal truncation rod measurement and density functional calculation. The energy gain due to the appearance of ferromagnetism in Pd results in flatter and uniform film growth of ferromagnetic Pd films compared with paramagnetic Pd. In addition, ferromagnetic Pd films expand the lattice constant in order to suppress the increase in kinetic energy of electrons accompanied by the occurrence of exchange splitting. Although the traditional theory of magnetism in metals indicates that the increase in density of states that induces ferromagnetism (Stoner criterion), our present finding reveals a mechanism of modulation in the density of states via the appearance of ferromagnetism, i.e., the inverse mechanism of Stoner's theory.