基于NiO的双磁性异质结构纳米晶体中的交换耦合调节,ACS Applied Materials & Interfaces - X-MOL

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基于NiO的双磁性异质结构纳米晶体中的交换耦合调节
ACS Applied Materials & Interfaces ( IF 8.3 ) Pub Date : 2021-05-17 , DOI: 10.1021/acsami.1c02855
Abdullah Al Shafe ₁ , Mohammad Delower Hossain ₂ , Robert A. Mayanovic ₁ , Vladimir Roddatis ₃ , Mourad Benamara ₄

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在不同的水溶液pH条件下，已经合成了一系列具有反铁磁性NiO核和亚铁磁性Mn _x Ni _{1- x} O和/或FiM Mn ₃ O ₄岛状纳米相过度生长的双磁异质结构纳米晶体。两步自组装过程采用热分解方法合成NiO纳米颗粒，然后生长Mn _x Ni _{1– x} O和/或Mn ₃ O ₄使用水热合成法在pH值为2.4-7.0的NiO核上形成纳米相。对环境无害的水热过程涉及在纳米颗粒表面发生的质子化与羟基化反应的pH控制。TEM分析和X射线衍射数据的Rietveld精修表明，三种不同类型的异质结构的纳米晶体的发生：氧化镍/锰_X的Ni _{1- X} ö核-壳状的异质结构以2.4 pH值，混合的NiO / Mn为_X的Ni _{1- X} O和/ </ / Mn ₃ O ₄核心过度生长结构，其<2.4 <pH <4.5，且主要为NiO / Mn ₃ O ₄pH> 4.5的核心岛结构。异质结构纳米晶体的磁性矫顽力和交换偏压随用于合成样品的水溶液的pH有系统地变化。与温度有关的磁化和磁滞回线数据与NiO磁芯的覆盖层性质一致。我们基于DFT的计算表明Mn _x Ni _{1– x} O相具有亚铁磁性质，沿着⟨111⟩取向具有稳定的自旋取向。此外，计算结果表明，Mn ₃ O ₄相的磁各向异性常数（K ₁）明显大于Mn _x Ni _1–_x的磁各向异性常数（K ₁）。O相，这由我们的实验结果证实。对于NiO / Mn ₃ O ₄核岛纳米晶体，矫顽力和交换偏压场最大，在pH值为5.0时合成，稳健值分别接近6 kOe和3 kOe。这项工作证明了在pH值的NiO核上Mn _x Ni _{1– x} O和/或Mn ₃ O ₄纳米相过度生长的水热沉积的可调谐性以及随之而来的磁矫顽力和交换偏置特性，这使得这些异质结构的纳米晶体潜在地可用于磁性设备，生物医学和其他应用。

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Tuning Exchange Coupling in NiO-Based Bimagnetic Heterostructured Nanocrystals

A series of bimagnetic heterostructured nanocrystals having an antiferromagnetic NiO core and a ferrimagnetic Mn_xNi_1–xO and/or FiM Mn₃O₄ island nanophase overgrowth has been synthesized under varying aqueous solution pH conditions. The two-step self-assembly process employs a thermal decomposition method to synthesize NiO nanoparticles, followed by growth of the Mn_xNi_1–xO and/or Mn₃O₄ nanophase over the NiO core using hydrothermal synthesis at pH values ranging from 2.4–7.0. The environmentally benign hydrothermal process involves pH control of the protonation vs hydroxylation reactions occurring at the nanoparticle surface. TEM analysis and Rietveld refinement of XRD data show that three distinct types of heterostructured nanocrystals occur: NiO/Mn_xNi_1–xO core–shell-like heterostructures at the pH of 2.4, mixed NiO/Mn_xNi_1–xO and/or/Mn₃O₄ core-overgrowth structures for 2.4 < pH < 4.5, and predominantly NiO/Mn₃O₄ core-island structures for pH > 4.5. The magnetic coercivity and exchange bias of the heterostructured nanocrystals vary systematically with the pH of the aqueous solution used to synthesize the samples. The temperature-dependent magnetization and hysteresis loop data are consistent with the nature of overlayer coverage of the NiO core. Our DFT based calculations show that the Mn_xNi_1–xO phase has ferrimagnetic properties with a stable spin orientation along the ⟨111⟩ orientation. Furthermore, the calculations show that the magnetic anisotropy constant (K₁) of the Mn₃O₄ phase is considerably larger than that of the Mn_xNi_1–xO phase, which is confirmed by our experimental results. The coercivity and exchange bias field are the largest for the NiO/Mn₃O₄ core-island nanocrystals, synthesized at a pH value of 5.0, with robust values of nearly 6 kOe and 3 kOe, respectively. This work demonstrates the tunability of hydrothermal deposition, and concomitant magnetic coercivity and exchange bias properties, of Mn_xNi_1–xO and/or Mn₃O₄ nanophase overgrowth over a NiO core with pH, that makes these heterostructured nanocrystals potentially useful for magnetic device, biomedical, and other applications.

更新日期：2021-05-26

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