Intercluster Interaction and Magnetic Interaction between Iron Core and Iron Oxide Shell in Core-Shell Nanoclusters
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Intercluster Interaction and Magnetic Interaction between Iron Core and Iron Oxide Shell in Core-Shell Nanoclusters Maninder Kaur, Qi Yao, and You Qiang Department of Physics and Environmental Science Program, University of Idaho, Moscow, ID 83844. U.S.A. ABSTRACT The intercluster interactions of iron/iron oxide core shell nanoclusters have been investigated, and their dependence on cluster size (d) has been discussed. A cluster deposition system is used to prepare core-shell nanoclusters with different d, varying from 9 to 14 nm.Transmission Electron Microscopy has been used for physical characterization, and Vibrating Sample Magnetometer for magnetic study. The cluster – cluster interactions have been investigated by field dependent isothermal remanent magnetization (IRM) and dc demagnetization (DCD) measurements at room temperature. Henkel plot shows more negative deviation from noninteracting case for bigger size nanoclusters than smaller size clusters. INTRODUCTION Three important effects namely finite-size effect, boundary effect, and effect of surface anisotropy play a significant role to distinguish magnetic nanoclusters from bulk material [1]. In a nanocluster assembly, the cluster interacts with each other by both magnetostatic and exchange interactions. Characterizing the interaction between clusters and core shell phases in a cluster is an important issue to increase the utilization of these systems in areas such as high density recording, ferrofluids, and biomedicine [2]. The coexistence of surface disorder and frustrated surface spins result in spin canting and spin glass like behavior that plays a significant role in interaction.We have studied the samples of iron nanoclustercovereduniformly by an oxide surface layer, prepared through the cluster source and gas aggregation technique [3-6]. Samples with different mean cluster sizes (9 nm -14 nm) were synthesized by controlling the gas ratio in the aggregation chamber. The physical characterizations such as compositional, structural, and magnetic properties were investigated by transmission electron microscopy (TEM), x-ray diffraction (XRD), and vibrating sample magnetometer (VSM) at room temperature. It can be concluded from the obtained results that the intercluster interaction is highly depended on the presence of iron to iron oxide ratio. The thermally activated surface spins inhibit the exchange interaction while the dipole moment of each cluster tends to magnetostatic interaction among the nanoclusters. EXPERIMENT Iron-Iron oxide (Fe-Fe3O4) core shell nanoclusters of variable mean cluster size of 9-14 nm were synthesized using nanocluster deposition system which is a combination of magnetron sputtering and gas aggregation techniques. The detailed deposition method is described in our previous papers [3,4]. In this study, the cluster size is controlled by changing the argon to helium gas ratio
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from 10 to 20 and keeping the other parameters such as power, aggregation length, and temperature constant. A small amount of oxygen (~ 2 sccm) in the
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