Orbital liquid state in ultrathin Pt/CoFeB films Open Access

Abstract

In this work, anomalous results observed in Anomalous Hall Effect and Brillouin Light Spectroscopy measurements of Co/Ni and CoFeB ultrathin films indicate the importance of orbital magnetism in describing these systems. These measurements are considered in the absence of an anomalous feature presence in Magneto-Optic Kerr Effect measurements of the same samples. The theoretical component of this work derives the presence of orbital correlations in ultrathin films of late transition metals, and effects of geometric frustration on a triangular lattice determine that the mismatch between orbital and crystal symmetries results in an orbital liquid state. Comparing solutions from independent-particle techniques, virtual hopping approximation techniques, and numerical simulations, it is evident that the independent-particle model is insufficient to describe our systems and that the virtual hopping approximation is more realistic. Applications of this orbital liquid state to technologically relevant phenomena are discussed, and the role of Pt in our experimental structures is explored.

Table of Contents

1 Introduction.............................................................................................................. 1

1.1  Motivation ............................................................................................................. 1

1.2  Background ............................................................................................................ 2

1.2.1  Phase transitions and Landau Theory..................................................................... 2

1.2.2  Anomalous Hall effect .......................................................................................... 3

1.2.3  Magneto-optical Kerr effect .................................................................................. 3

1.2.4  Field theoretical language .................................................................................... 4

1.2.5  BCS, Mott, and Kugel-Khomskii systems ................................................................6

2  Experimental Work ................................................................................................... 7

2.1  Methods (AHE) .......................................................................................................7

2.2  Results and Discussion ............................................................................................8

2.2.1  AHE in Co/Ni films ............................................................................................... 8

2.2.2  Experimental work of collaborators: AHE in CoFeB films ........................................ 10

2.2.3  Experimental work of collaborators: MOKE ........................................................... 11

2.2.4  Experimental work of collaborators: BLS ............................................................... 12

3  Theoretical Work .....................................................................................................  15

3.1  Motivation ............................................................................................................ 15

3.2  Methods ............................................................................................................... 16

3.3  Results and Discussion .......................................................................................... 17

3.3.1  Orbital correlations ............................................................................................ 17

3.3.2  Geometric frustration ......................................................................................... 18

3.3.3  Application to PMA ............................................................................................ 21

3.3.4  Role of Pt .......................................................................................................... 23

4  Conclusions ...........................................................................................................  24

About this Honors Thesis

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School	Emory College
Department	Physics
Degree	B.S.
Submission	Honors Thesis
Language	English
Research Field	Physics, Condensed Matter
Keyword	magnetism physics condensed matter physics
Committee Chair / Thesis Advisor	Sergei Urazhdin, Emory University
Committee Members	Jed Brody, Emory University Hayk Harutyunyan, Emory University Maja Taskovic, Emory University

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