# Structural Evolution of Printed Ternary Magnetic Hybrid Thin Films Containing Soft and Hard Magnetic Nanoparticles for Coupled Composites

## TL;DR

This paper studies how combining soft and hard magnetic nanoparticles in printed thin films can create materials with tunable magnetic properties for use in permanent magnets and microwave devices.

## Contribution

The study demonstrates how dipolar coupling in ternary magnetic nanocomposites can enhance coercivity without complex material synthesis.

## Key findings

- Ternary films show a single-phase hysteresis loop at 300 K that becomes two-phase at lower temperatures.
- The ternary film exhibits higher coercivity than the binary film due to dipolar coupling between nanoparticles.
- GISAXS and AFM reveal similar film formation kinetics and surface morphology across all samples.

## Abstract

Diblock copolymer thin films templating two types of
magnetic nanoparticles
are ternary nanocomposites that can show tunable magnetic behavior
depending on the size and magnetic properties of the nanoparticles.
In the case of utilizing both soft and hard magnetic nanoparticles,
the ternary films become interesting for applications in permanent
magnets and microwave devices. In this work, ternary hybrid thin films
composed of the diblock copolymer polystyrene-block-poly­(methyl methacrylate) (PS-b-PMMA), cobalt ferrite
(CoFe2O4, d = 21.7 ± 12.2
nm) nanoparticles, and nickel (Ni, d = 46 ±
10 nm) nanoparticles are fabricated from solution in a slot-die printing
process. The film morphology evolution is tracked in situ by grazing-incidence small-angle X-ray scattering (GISAXS). For
comparison, a binary hybrid film with only PS-b-PMMA
and CoFe2O4 nanoparticles and a pure PS-b-PMMA film are also investigated. All films show similar
kinetics during film formation, where the wet film undergoes solvent
evaporation followed by rapid microphase separation and coalescence
into the final dry film. Complementary atomic force microscopy (AFM)
measurements reveal the as-printed surface morphology of the polymer
nanocomposites. To probe the magnetic behavior of the hybrid thin
films, a superconducting quantum interference device (SQUID) magnetometer
is used to measure the magnetic response in both the in-plane direction
and out-of-plane direction. The ternary film shows a single-phase
hysteresis loop at 300 K that evolves into a two-phase hysteresis
as the temperature is decreased, as the soft and hard magnetic phases
switch individually. Compared to the binary film, the ternary film
shows increased coercivity over the measured temperature range due
to dipolar coupling between the NPs in the system. Thus, the ternary
film demonstrates the potential for utilizing dipolar interactions
in the fabrication of coupled composites, allowing for the tuning
of magnetic behavior without the need for complex material synthesis.