Date of Award

2022-05-01

Degree Name

Master of Science

Department

Physics

Advisor(s)

Mark R. Pederson

Abstract

Molecules and materials constructed from Mn atoms offer diverse assortments of geomet- rical and spin structures. The diversity of structures, in comparison with other transition metals, along with nature’s decision to use a Mn-based molecule to catalyze solar-driven water splitting and oxygen evolution, suggests that there is indeed something special about the location of Mn valence electrons, both energetically and geometrically, that endows Mn with its multifaceted behaviors that, in turn, provide such chemical, physical and mag- netic diversity. Based upon recent work on the Mn3 monomer and the Mn(taa) there is an expectation that Mn�� �� �� centers can exist in local spin states with S=2 (3��↑↑↑↑) or S=1 (3��↑↑↑↓). While the high-spin states are usually more stable based on Hund’s first rule, the Mn3 monomer and the ����(������) provide examples where the presence of S=1 states is energetically favorable. In this work we examine the possibility that such S=1 cen- ters, referred to as Spin-Flip Excitons (SFE) can exist in the Mn12O12(COOR)16[H2O]2 molecule (Mn12-Ac). Our results shown that up to eight of these excitons can exist as metastable electronic states. We examine the relative stability per exciton as a function of the number of these excitons and determine spin-crossover paths between the Mn12-Ac zero-exciton ground state (S=10), a four-exciton state (S=6) and an eight-exciton state (S=2). The magnetic anisotropy of these states decreases monotonically and significantly with the number of excitons. In other words the creation of excitons provides a means for switching the magnetic strength.

Language

en

Provenance

Received from ProQuest

File Size

77 p.

File Format

application/pdf

Rights Holder

Karma Dema

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Physics Commons

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