In this study, we demonstrate a synthesis of rhodium substituted 3-iron oxide, 3-Rh x Fe 2Àx O 3 (0 # x # 0.19), nanoparticles in silica. The synthesis features a sol-gel method to coat the metal hydroxide sol containing Fe 3+ and Rh 3+ ions with a silica sol via hydrolysis of alkoxysilane to form a composite gel. The obtained samples are barrel-shaped nanoparticles with average long-and short-axial lengths of approximately 30 nm and 20 nm, respectively. The crystallographic structure study using X-ray diffraction shows that 3-Rh x Fe 2Àx O 3 has an orthorhombic crystal structure in the Pna2 1 space group. Among the four nonequivalent substitution sites (A-D sites), Rh 3+ ions mainly substitute into the C sites. The formation mechanism of 3-Rh x Fe 2Àx O 3 nanoparticles is considered to be that the large surface area of the nanoparticles increases the contribution from the surface energy to Gibbs free energy, resulting in a different phase, 3-phase, becoming the most stable phase compared to that of bulk or single crystal. The measured electromagnetic wave absorption characteristics due to natural resonance (zero-field ferromagnetic resonance) using terahertz time domain spectroscopy reveal that the natural resonance frequency shifts from 182 GHz (3-Fe 2 O 3) to 222 GHz (3-Rh 0.19 Fe 1.81 O 3) upon rhodium substitution. This is the highest natural resonance frequency of a magnetic material, and is attributed to the large magnetic anisotropy due to rhodium substitution. The estimated coercive field for 3-Rh 0.19 Fe 1.81 O 3 is as large as 28 kOe.

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In mobile ad-hoc networks (MANETs), there are selfish nodes, which drop the received data packets, because nodes have limits of their resources. Secure routing protocols are developed as one of security mechanisms. In secure routing, each node can detect selfish nodes and decide secure paths by consulting trust values. Here, trust values express reliability for nodes or paths. In these existing routing protocols, all nodes are assumed to keep the same behavior in order to obtain the stable trust values. However, there are selfish nodes with behavior changes because resources for these mobile nodes decrease as time passes. Therefore, as it is hard to calculate accurate trusts in nodes with behavior change in real time, there are two problems. One is to make a mistake in judgment of selfish nodes and the other is not to be able to select the secure paths. In this paper, we propose TEAB, which is a trust evaluation method adapted to node behavior. We introduce the adaptive time window which is the time period for evaluating a trust value. Each node uses a variable time window for each neighbor and reduces the undesirable effects of past behaviors. In this way, each node calculates trust values correctly in the environment including nodes with behavior change. Moreover, in secure routing protocols using TEAB, each node can select the secure communication path composed of only cooperative nodes. The results of simulation show that each node can detect the selfish nodes correctly and start to communicate through the secure path by using TEAB.

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