Meron Tal, Markovich Gil
School of Chemistry, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, Tel Aviv 69978, Israel.
J Phys Chem B. 2005 Nov 3;109(43):20232-6. doi: 10.1021/jp0539775.
High-temperature hydrolysis of Zn(II) and Mn(II) alkoxides in a high boiling point solvent in the presence of surfactants was used to prepare surfactant-coated Zn(1-x)Mn(x)O nanocrystals with average size of 5.5 nm and x = 0.04 +/- 0.03. The magnetic properties of the nanocrystals were measured both for isolated particles diluted in a hydrocarbon matrix and for a nanocrystal powder. Nanocrystals of manganese oxide and ZnO coated with manganese oxide were prepared for comparison to the Zn(1-x)Mn(x)O nanocrystals. We find that the manganese ions primarily substitute zinc ions in the hexagonal ZnO lattice, and part of them are ferromagnetically coupled up to room temperature even in isolated noninteracting nanocrystals. The rest of the ions are magnetically disordered or uncoupled. Surprisingly, these small Zn(1-x)Mn(x)O nanocrystals poses relatively large low-temperature magnetic coercivity and relatively high blocking temperature in the isolated form, which indicate large magnetic anisotropy. In the nanocrystal powder the coercive field decreased significantly. This study highlights the advantages of working with noninteracting single domain particles of these intriguing materials.
在表面活性剂存在的情况下，于高沸点溶剂中对锌（II）和锰（II）醇盐进行高温水解，以制备平均尺寸为5.5纳米且x = 0.04±0.03的表面活性剂包覆的Zn(1-x)Mn(x)O纳米晶体。对稀释于烃类基质中的孤立颗粒以及纳米晶体粉末均测量了纳米晶体的磁性。制备了氧化锰纳米晶体以及包覆有氧化锰的氧化锌纳米晶体，以与Zn(1-x)Mn(x)O纳米晶体进行比较。我们发现，锰离子主要替代六方ZnO晶格中的锌离子，并且即使在孤立的非相互作用纳米晶体中，其中一部分在室温下也呈现铁磁耦合。其余离子则磁无序或未耦合。令人惊讶的是，这些小的Zn(1-x)Mn(x)O纳米晶体在孤立形式下具有相对较大的低温磁矫顽力和相对较高的阻塞温度，这表明其具有较大的磁各向异性。在纳米晶体粉末中，矫顽场显著降低。这项研究突出了使用这些有趣材料的非相互作用单畴颗粒进行研究的优势。
