Vibrational frequencies of magnetic random access memory materials / Lee Li Ling

Lee, Li Ling (2010) Vibrational frequencies of magnetic random access memory materials / Lee Li Ling. Masters thesis, University of Malaya.

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Abstract

The advantages of MRAM are so overwhelming which acts as motivation for scientist in further investigation for better read and write operation. The types of materials used are closely related to the cell performance in forming the ferromagnetic layers. Thus,the vibrational frequencies of the MRAM materials are of interest. Clusters for the two types of combinations, FexNiy and FexCoyBz are built. Subsequently, vibrational frequencies of each cluster are calculated theoretically from the first principles. The secular determinant is large when the number of electrons in a cluster is large. For the simplest combination of Fe-Ni cluster, (atomic number of an iron atom is 26 and a nickel atom is 28) gives secular determinant of 26 × 26 and 28 × 28 respectively. As the atomic number increases, the matrix becomes larger which is unlikely to be solved manually. These types of matrices are solved by a quadro computer operating at 2.83GHz with a good computer programme with suitable approximations. The density functional theory (DFT) is used to optimize the bond lengths and angles of the clusters for the minimum energy of the Schrödinger equation by using double zeta (DZ) and double zeta with polarized (DZP) wave functions. The bond distance calculated for cluster Fe-Ni is 213.4 picometer and the vibrational frequency shows a peak at 316.5 cm-1 (intensity = 0.002 km/mole). Larger size clusters show more vibrational frequencies. Cluster Fe4Co3B4 shows 16 peaks with the largest peak at 1147.7 cm-1. The structure of the atomic combination is important in predicting which material works the best for memory performance. Calculations for several different ratios of the constituent atoms are performed.

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