Zheng Yuruo, Hussain Ghulam, Li Shuyi, Batool Shanta, Wang Xiawa
Department of Natural and Applied Sciences Duke Kunshan University, Suzhou 215316, China.
Department of Physics, and Key Laboratory of Strongly-Coupled Quantum Matter Physics (CAS), University of Science and Technology of China, Hefei 230026, China.
Nanomaterials (Basel). 2022 Aug 18;12(16):2839. doi: 10.3390/nano12162839.
In this work, nanoparticles of CoReFeO and CoFeReO (0 ≤ x ≤ 0.05) were synthesized by the sol-gel method. The Rietveld refinement analysis of XRD and Raman data revealed that all of the prepared samples were single phase with a cubic spinel-type structure. With the substitution of Re, the lattice parameters were slightly increased, and Raman spectra peak positions corresponding to the movement of the tetrahedral sublattice shifted to a higher energy position. Furthermore, Raman spectra showed the splitting of T mode into branches, indicating the presence of different cations at crystallographic A- and B-sites. The SEM micrograph confirms that surface Re exchange changes the coordination environment of metals and induces Fe-site structure distortion, thereby revealing more active sites for reactions and indicating the bulk sample's porous and agglomerated morphology. The vibrating sample magnetometer (VSM) results demonstrated that the synthesized nanoparticles of all samples were ferromagnetic across the entire temperature range of 300-4 K. The estimated magnetic parameters, such as the saturation magnetization, remanent magnetization, coercivity, blocking temperature (), and magnetic anisotropy, were found to reduce for the Co-site doping with the increasing doping ratio of Re, while in the Fe site, they enhanced with the increasing doping ratio. The ZFC-FC magnetization curve revealed the presence of spin-glass-like behavior due to the strong dipole-dipole interactions in these ferrite nanoparticles over the whole temperature range. Finally, the dielectric constant () and dielectric loss () were sharply enhanced at low frequencies, while the AC conductivity increased at high frequencies. The sharp increases at high temperatures are explained by enhancing the barrier for charge mobility at grain boundaries, suggesting that samples were highly resistive. Interestingly, these parameters (, ) were found to be higher for the Fe-site doping with the increasing Re doping ratio compared with the Co site.
在本工作中，采用溶胶-凝胶法合成了CoReFeO和CoFeReO（0≤x≤0.05）的纳米颗粒。对XRD和拉曼数据进行的Rietveld精修分析表明，所有制备的样品均为具有立方尖晶石型结构的单相。随着Re的取代，晶格参数略有增加，并且对应于四面体亚晶格移动的拉曼光谱峰位置移向更高能量位置。此外，拉曼光谱显示T模式分裂成多个分支，表明在晶体学A位和B位存在不同的阳离子。扫描电子显微镜（SEM）显微照片证实，表面Re交换改变了金属的配位环境并诱导了Fe位结构畸变，从而揭示了更多的反应活性位点，并表明块状样品具有多孔和团聚的形态。振动样品磁强计（VSM）结果表明，所有样品合成的纳米颗粒在300 - 4 K的整个温度范围内均为铁磁性。发现随着Re掺杂比例的增加，Co位掺杂的估计磁参数，如饱和磁化强度、剩余磁化强度、矫顽力、阻塞温度（）和磁各向异性降低，而在Fe位，它们随着掺杂比例的增加而增强。零场冷却-场冷却（ZFC-FC）磁化曲线表明，由于这些铁氧体纳米颗粒在整个温度范围内存在强偶极-偶极相互作用，因此存在类似自旋玻璃的行为。最后，介电常数（）和介电损耗（）在低频时急剧增强，而交流电导率在高频时增加。高温下的急剧增加是由于晶界处电荷迁移势垒的增强所致，这表明样品具有高电阻性。有趣的是，与Co位相比，随着Re掺杂比例的增加，Fe位掺杂的这些参数（，）更高。
