Large exchange bias and enhanced coercivity in strongly-coupled Ni/NiO binary nanoparticles

Area of Science:

• Materials Science
• Nanotechnology
• Condensed Matter Physics

Background:

• Nanoparticles composed of magnetic and non-magnetic materials offer unique properties.
• The interface between different phases in nanomaterials significantly influences their characteristics.
• Understanding complex magnetic behaviors in binary systems is crucial for developing new magnetic applications.

Purpose of the Study:

• To synthesize Ni/NiO binary nanoparticles using a reflux and calcination method.
• To investigate the impact of microstructure and phase states on the magnetic properties of Ni/NiO nanoparticles.
• To analyze the complex magnetic behaviors arising from the interplay of ferromagnetic, antiferromagnetic, and spin-glass-like phases.

Main Methods:

• Synthesis of Ni/NiO binary nanoparticles via a reflux method followed by calcination.
• Characterization of nanoparticle size (5-20 nm) and Ni content (3.55%).
• Magnetic property measurements, including coercivity (H_C) and exchange bias (H_E), at varying temperatures and cooling fields.

Main Results:

• Large exchange bias (H_E = 482 Oe) and enhanced coercivity (H_C = 1335 Oe) were observed at 5 K.
• Complex magnetic behaviors were attributed to the ferromagnetic Ni nanoparticles, antiferromagnetic NiO bulk phase, and disordered NiO surface.
• Strong coupling interaction between Ni and NiO components was identified as the primary driver for enhanced magnetic properties.

Conclusions:

• The synthesized Ni/NiO binary nanoparticles demonstrate a strongly-coupled system with improved magnetic performance.
• The interplay of multiple magnetic phases (ferromagnetic, antiferromagnetic, spin-glass-like) contributes to the observed complex magnetic behaviors.
• These findings suggest potential applications for Ni/NiO binary nanoparticles in advanced magnetic materials and devices.