Surface Effects on Morin Transition, Exchange Bias, and Enchanced Spin Reorientation in Chemically Synthesized DyFeO3 Nanoparticles

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• 作者：Adhish Jaiswal ; Raja Das ; Suguna Adyanthaya ; Pankaj Poddar
• 刊名：Journal of Physical Chemistry C
• 出版年：2011
• 出版时间：February 24, 2011
• 年：2011
• 卷：115
• 期：7
• 页码：2954-2960
• 全文大小：936K
• 年卷期：v.115,no.7(February 24, 2011)
• ISSN：1932-7455

文摘

A giant linear magnetoelectric effect was observed by Y. Tokura鈥檚 group recently in multiferroic DyFeO₃, which demands a detailed investigation of its magnetic properties. Additionally, there is little information on the changes of chemical and physical properties of these materials with the reduction in particle size in spite of the potential applications of these materials in nanoscale devices. As the wet-chemical synthesis of these materials in nanosize and getting a control over crystallinity and stoichiometry is nontrivial and poses a serious challenge prohibiting the study of their size-dependent properties. Here, we report the synthesis of DyFeO₃ nanoparticles using a surfactantless hydrothermal method with a detailed magnetic property measurement. The as-synthesized DyFeO₃ nanoparticles showed excellent crystallinity with average particle size in the range 50鈭?0 nm. The structural analysis indicated that they are of a distorted orthorhombic pervoskite crystal structure. Detailed dc magnetization measurements in the temperature range of 3鈭?50 K could isolate the presence of Dy³⁺鈭扚e³⁺ and Dy³⁺鈭扗y³⁺ superexchange interactions, which showed up as spin reorientation transitions in various temperature regions due to the differing magnitude of their interactions resulting in continuous rotation of antiferromagnetic component of Fe³⁺ spins with cooling of the sample. Nanosized DyFeO₃ showed spin-reorientation transitions near 315 and 70 K due to the Dy³⁺鈭扚e³⁺ interaction accompanied with an opening up of the hysteresis loop followed by antiferromagnetic ordering around 4 K due to a possible Dy³⁺鈭扗y³⁺ interaction. We also observed significant effect of the particle size reduction on the magnetic properties. The main effects seen by us were in terms of (1) pronounced spontaneous spin reorientation transitions, (2) the absence of Morin transition, and (3) presence of temperature-dependent exchange bias in the DyFeO₃ nanoparticles. We present a detailed mechanism to explain these features based on the interplay of Dy³⁺ and Fe³⁺ spins as well surface disorder, anisotropy, canting, and so forth.