The core–shell Fe₃O₄@ZrO₂ nanoparticles with controllable shell thickness and core dimensions are synthesized using solvothermal approaches. The introduction of the insulator ZrO₂ shell allows realizing the enhancement of tunneling magnetoresistance (TMR) effect of the functional nanomaterials. The influences of temperature, magnetic field, and shell thickness on the TMR are explored. With the shell thickness ≈3 nm TMR ratio of 10% is obtained, which improves the MR compared to the pure Fe₃O₄ counterpart of 5.7%. Furthermore, the MR is increased first and then decreases with increase of the shell thickness, which suggests that the addition of insulated shell‐layer promotes the electron tunneling among the supraparticles and thereby increases the MR. The fault‐cutting data indicate that the tunneling mechanism occurs mainly through the magnetic‐insulator interfaces rather than the interior nanoparticle interfaces. In addition, the MR with different core‐size presents a monotonic increase with decrease of the size of core.

中文翻译：

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可调厚度的ZrO2壳层对增强Fe3O4超粒子隧穿磁阻的影响

使用溶剂热法合成了具有可控制的壳厚度和核尺寸的核-壳Fe ₃ O ₄ @ZrO ₂纳米颗粒。绝缘体ZrO ₂壳的引入允许实现功能纳米材料的隧穿磁阻（TMR）效应的增强。探索了温度，磁场和壳厚度对TMR的影响。壳厚度≈3nm时，TMR比率为10％，与纯Fe ₃ O ₄相比，MR得以改善对应的是5.7％。此外，MR会先增加，然后随壳厚度的增加而减小，这表明添加绝缘壳层会促进超粒子之间的电子隧穿，从而增加MR。断层数据表明，隧穿机理主要是通过电绝缘体界面而不是内部纳米粒子界面发生的。另外，具有不同芯尺寸的MR随芯尺寸的减小而呈现单调增加。