A Size Threshold for Enhanced Magnetoresistance in Colloidally Prepared CoFe₂O₄ Nanoparticle Solids

Abstract

The phenomenon of granular magnetoresistance offers the promise of rapid functional materials discovery and high-sensitivity, low-cost sensing technology. Since its discovery over 25 years ago, a major challenge has been the preparation of solids composed of well-characterized, uniform, nanoscale magnetic domains. Rapid advances in colloidal nanochemistry now facilitate the study of more complex and finely controlled materials, enabling the rigorous exploration of the fundamental nature and maximal capabilities of this intriguing class of spintronic materials. We present the first study of size-dependence in granular magnetoresistance using colloidal nanoparticles. These data demonstrate a strongly nonlinear size-dependent magnetoresistance with smaller particles having strong ΔR/R ∼ 18% at 300 K and larger particles showing a 3-fold decline. Importantly, this indicates that CoFe2O4 can act as an effective room temperature granular magnetoresistor and that neither a high superparamagnetic blocking temperature nor a low overall resistance are determining factors in viable magnetoresistance values for sensing applications. These results demonstrate the promise of wider exploration of nontraditional granular structures composed of nanomaterials, molecule-based magnets, and metal-organic frameworks.

Spin-polarized oxygen evolution reaction under magnetic field

“…Besides, the electrical resistance of magnetic materials can be affected by the magnetization, which is through the scattering of electrons on the magnetic lattice of the crystal. 38 – 40 However, the difference in the conductivity at room temperature under 10,000 Oe is about 3% for insulator CoFe 2 O 4 with 3.86 × 10 −5 S/m, 40 – 42 which does not cause a significant difference in the electrode’s conductivity. This is because acetylene black carbon (AB) with 500 S/m as a conductive mediator is mixed with those oxide catalysts for their application as the electrode, 43 which dominants the electron conduction.…”

The role of nanoparticle size and ligand coverage in size focusing of colloidal metal nanoparticles

“…[1][2][3][4][5][6] For example, recent synthetic methods enabled fabrication of colloidal nanoparticles with different sizes by simply altering the reaction conditions (solvent, ligand, precursor, and synthesis temperature). [7][8][9][10][11] However, since the size distribution of the nanoparticles is oen key to their specic, desired physical and chemical properties, [12][13][14][15][16][17][18] a fundamental understanding of how to control the nucleation and growth is key to enable predictive synthesis of nanoparticles with the desired properties. To date, different models and mechanisms have been proposed to describe the nucleation and growth of colloidal nanoparticles as well as size focusing and defocusing.…”

Spin-Polarized Oxygen Evolution Reaction Under Magnetic Field

“…Besides, the electrical resistance of magnetic materials can be affected by the magnetization, which is through the scattering of electrons on the magnetic lattice of the crystal. [38][39][40] However, the difference in the conductivity at room temperature under 10000 Oe is about 3% for insulator CoFe2O4 with 3.86×10 -5 S/m, [40][41][42] which does not cause a significant difference in the electrode's conductivity. This is because acetylene black carbon (AB) with 500 S/m as a conductive mediator is mixed with those oxide catalysts for their application as the electrode, 43 which dominants the electron conduction.…”