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.

中文翻译：

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胶体制备的CoFe ₂ O ₄纳米颗粒固体中增强磁致电阻的尺寸阈值

粒状磁阻现象为快速发现功能材料和高灵敏度，低成本的传感技术提供了希望。自从25年前发现以来，主要的挑战是制备由特征明确，均匀的纳米级磁畴组成的固体。胶体纳米化学的飞速发展现在促进了对更复杂和精细控制的材料的研究，从而使人们能够对这种有趣的自旋电子学材料的基本性质和最大能力进行严格的探索。我们目前使用胶体纳米粒子对颗粒磁阻的尺寸依赖性进行了首次研究。这些数据证明了尺寸大小的强非线性磁阻，较小的颗粒具有很强的ΔR / R在300 K时约为18％，较大的颗粒则下降3倍。重要的是，这表明CoFe ₂ O ₄可以充当有效的室温粒状磁阻，并且高的超顺磁阻挡温度和低的总电阻都不是感测应用中可行的磁阻值的决定因素。这些结果证明了对由纳米材料，基于分子的磁体和金属有机骨架组成的非传统颗粒结构进行更广泛研究的希望。