Magnetic Properties of Embedded Rh Clusters in Ni Matrix
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Zhi-Qiang LI, Yuichi Hashi*, Jing-Zhi YU, Kaoru OHNO, and Yoshiyuki KAWAZOE Institute for Materials Research, Tohoku University, Sendai 980-77, Japan * Hitachi Tohoku Software Ltd., Research and Development Center, Sendai 980, Japan
ABSTRACT The electronic structure and magnetic properties of rhodium clusters with sizes of 1 - 43 atoms embedded in the nickel host are studied by the first-principles spin-polarized calculations within the local density functional formalism. Single Rh atom in Ni matrix is found to have magnetic moment of 0. 45 PB. Rh 13 and Rhl 9 clusters in Ni matrix have lower magnetic moments compared with the free ones. The most interesting finding is tha.t Rh 43 cluster, which is bulk-like nonmagnetic in vacuum, becomes ferromagnetic when embedded in the nickel host.
INTRODUCTION Atomic clusters have opened new prospects in the development of materials science. Taking advantage of the characteristic behavior of small particles, one expects to be able to tailor new materials for specific technological purposes. Consequently, much effort has been invested in the research on the properties of microclusters[1]. Rhodium has specially interesting magnetic properties. It is nonmagnetic in the bulk state. However, the rhodium nmonolayer on all iron substrate has a measured magnetic moment of 0.82 /it per atom [6]. Since Reddy, Khanna and Dunlap[2] predicted that small rhodium clusters show the ferro-
magnetic properties, many experimental and theoretical investigations havc been conducted to explore the unusual magnetic properties of rhodium clusters[3, 4, 5]. Using the local-spin-density (LSD) functional theory, Reddy, Khalna and Dunlap[2] recently calculated the magnetic moments for ruthernium, rhodium, and palladium 13atom clusters with icosahedral and cubo-octahedral symmetry. They predicted moments of 1.62 1t B per atom for icosaledral Rh13, 1.02 PB per atom for icosaledral Ru1 3 , and 0.12;.13 for icosaledral Pd 13 . Indeed, Cox et al.[3] observed experimentally giant magnetic moments in small Rh,, clusters with n=12-34. However, their observed value of the average magnetic moment per atom for Rhl3 is 0. 4 8 PB, only about one-third of the theoretical prediction of Reddy et al.. They also found that the average moment per atom of the Rh clusters depends significantly on the cluster size. There are several sizes, R.h15 , Rh1 6 , and Rh1 9 which have magnetic moments per atom that are significantly larger than those of adjacent cluster sizes. The average moment of the rhodium cluster decreases to the bulk value of zero as the cluster size increases. Yang et al.[4] have also performed first principles studies on Rh,, (n=2-19) clusters, and they did not observe the magnetic transition from magnetic state to nonmagnetic state as the cluster size increases, due to small number of atoms in their studies. We have studied the electronic structure and magnetic properties of Rh,, (n=6, 9, 13, 19, 43) clusters and obtained better results compared with the experiments[5]. Moreover, 535 Mat. Res. Soc. Symp. P
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