Magnetic Memory Effect of Nanocomposites

Abstract

The magnetic memory effect (MME) is the ability of magneto-sensitive materials to remember the magnetic field strength (H_def), at which they were deformed recently. They respond close to H_def either by recovering their initial shape at a switching magnetic field strength H_sw under stress-free conditions or by building up stress with a peak maximum at H_σ,max under constant strain conditions. This paper explores whether such a MME can be created for polymer-based nanocomposites. The concept is based on temperature-memory polymers (TMP) as matrix, in which silica coated iron(III)oxide nanoparticles (mNP) are dispersed. The MME was explored in a cyclic magneto-mechanical test, in which the nanocomposite sample was elongated to ϵ_m while being exposed to an alternating magnetic field at H_def. The magnetic memory was read out by determining H_σ,max or H_sw. A linear correlation between H_σ,max (or H_sw) and H_def in a range from 15 to 23 kA m⁻¹ at a fixed frequency of f = 258 kHz is observed and demonstrates the excellent magnetic memory properties of the investigated nanocomposites containing either crystallizable or amorphous, vitrifiable domains as controlling units. The deformation ϵm at H_def can be fixed with an accuracy of more than 72% and the initial shape can be recovered almost completely by more than 86%. The MME allows the design of magnetically programmable devices such as switches or mechanical manipulators.