Mihalache V, Negrila C, Mercioniu I, Iacob N, Kuncser V
National Institute of Materials Physics, 077125, Magurele, Romania.
Phys Chem Chem Phys. 2021 Aug 4;23(30):16107-16127. doi: 10.1039/d1cp01002f.
Zn-Fe-O nanoparticle systems (Z3F, Z20F and Z60F) were produced by changing the Zn:Fe ratio (0.97 : 0.03, 0.8 : 0.2 and 0.4 : 0.6 in at%, respectively) in Zn(ii)-Fe(iii)-carboxylate precursors. According to X-ray diffraction, Z60F is nearly single-phase ZnFe2O4 (5.9 nm crystallite size), Z20F is a ZnO/ZnFe2O4 nanocomposite consisting of 48.8% ZnFe2O4 (4.7 nm crystallite size), and Z3F is apparently pure ZnO (9.5 nm). We found evidence for a ZnFe2O4 spinel of high inversion degree (80-100%) and with superparamagnetic (SPM) behaviour at room temperature in all three samples by a remarkable correlation between HRTEM, FTIR, XPS, Mössbauer and magnetization analyses. Iron modifies the decomposition process of the precursor and enhances its viscosity, which appears to favour the separation of Zn- and Fe-rich phases. As a consequence, two-phase systems of individual nanocrystals/nanoparticles (ZnO and ZnFe2O4) are formed. The large anisotropy constant, 106-107 erg cm-3, of the ZnFe2O4 nanoparticles and the concentration dependence of their magnetic energy barrier are explained in terms of interparticle interactions interlinked with finite size effects and high inversion degree; these factors also control the other parameters of importance for applications, including the blocking temperature (13-111 K), saturation magnetization (1.08-17.7 emu g-1 at 300 K, 4.6-44.8 emu g-1 at 5 K) and coercivity (85.4-491 Oe at 5 K). Magnetic dynamic results, particularly modelled by the Néel-Brown and Vogel-Fulcher laws, yield fitting parameters which validate the presence of concentration-dependent dipole-like interactions between ZnFe2O4 nanoparticles. A fraction of iron was found in the Fe2+ state, presumably substituting for Zn2+ in zinc oxide; however, the samples behave like ZnFe2O4 SPM nanoclusters/nanoparticles dispersed in a nonmagnetic ZnO particle assembly, rather than Zn(Fe)O dilute magnetic semiconductors. The relevance of the properties of the investigated material for specific applications is highlighted throughout the manuscript.
通过改变锌（II） - 铁（III） - 羧酸盐前驱体中的锌与铁的比例（原子百分比分别为0.97∶0.03、0.8∶0.2和0.4∶0.6）制备了锌 - 铁 - 氧纳米颗粒体系（Z3F、Z20F和Z60F）。根据X射线衍射结果，Z60F几乎是单相的ZnFe₂O₄（微晶尺寸为5.9纳米），Z20F是由48.8%的ZnFe₂O₄（微晶尺寸为4.7纳米）组成的ZnO/ZnFe₂O₄纳米复合材料，而Z3F显然是纯ZnO（9.5纳米）。通过高分辨率透射电子显微镜（HRTEM）、傅里叶变换红外光谱（FTIR）、X射线光电子能谱（XPS）、穆斯堡尔谱和磁化分析之间的显著相关性，我们在所有三个样品中发现了具有高反转度（80 - 100%）且在室温下具有超顺磁性（SPM）行为的ZnFe₂O₄尖晶石的证据。铁改变了前驱体的分解过程并提高了其粘度，这似乎有利于富锌相和富铁相的分离。结果，形成了由单个纳米晶体/纳米颗粒（ZnO和ZnFe₂O₄）组成的两相体系。ZnFe₂O₄纳米颗粒的大各向异性常数（10⁶ - 10⁷尔格·厘米⁻³）及其磁能垒的浓度依赖性可以用与有限尺寸效应和高反转度相关的颗粒间相互作用来解释；这些因素还控制着其他对应用很重要的参数，包括阻塞温度（13 - 111 K）、饱和磁化强度（在300 K时为1.08 - 17.7电磁单位·克⁻¹，在5 K时为4.6 - 44.8电磁单位·克⁻¹）和矫顽力（在5 K时为85.4 - 491奥斯特）。磁动力学结果，特别是由奈尔 - 布朗和沃格尔 - 富尔彻定律建模的结果，得出的拟合参数验证了ZnFe₂O₄纳米颗粒之间存在浓度依赖性偶极样相互作用。发现一部分铁处于Fe²⁺状态，大概是在氧化锌中替代了Zn²⁺；然而，这些样品的行为类似于分散在非磁性ZnO颗粒集合体中的ZnFe₂O₄ SPM纳米团簇/纳米颗粒，而不是Zn（Fe）O稀磁半导体。在整个手稿中都强调了所研究材料的性质对于特定应用的相关性。
