Dissertation/Thesis Abstract

Tuning coercivity via iron chains in phthalocyanine thin films
by Werber, Mathew Stephen, M.S., California State University, Long Beach, 2013, 89; 1523066
Abstract (Summary)

We investigated the properties of magnetic hysteresis loops of Iron Phthalocyanine (FePc) thin films using a Vibrating Sample Magnetometer (VSM). The FePc thin films were deposited onto heated silicon substrates. During deposition the FePc molecules self-assemble into small crystallites ranging in size from 30 to 300 nm on average. Due to the planar shape of the molecule, chains of iron atoms are formed. The magnetic interaction within a chain is much stronger than between chains, making these thin films quasi-one-dimensional magnetic systems. The average length of the major axis of the grains increases with the temperature of the substrate (deposition temperature). Essentially the thin films are made up of many randomly oriented iron chains of variable length, which are parallel to the substrate surface. We show that the coercivity of hysteresis loops measured at 2 K increases linearly with the average major axis grain length. From interpolation, the minimum average grain length for hysteresis to occur is 8 nm, and every additional nano-meter in length increases the coercivity by 72 Oe. By measuring hysteresis loops of many thin films of varying thickness we found that the saturation magnetization is 31 emu/cm3. This corresponds to 2.0 ± 0.6 µ B per iron ion, as compared to 2.22 µB for iron in a 3D lattice at 0 K. The choice of substrate also affects the hysteresis properties. Samples deposited on silicon substrates that had first been coated in gold with a rms roughness of approximately 1 nm will show much lower coercivity than corresponding silicon substrate samples. The planar gold surface allows for a different growth pattern in which the chains form vertically, perpendicular to the substrate. This lower coercivity suggests that the chains are shorter when vertically oriented.

Indexing (document details)
Advisor: Gredig, Thomas
Commitee: Bill, Andreas, Gu, Jiyeong
School: California State University, Long Beach
Department: Physics
School Location: United States -- California
Source: MAI 52/01M(E), Masters Abstracts International
Subjects: Physics
Publication Number: 1523066
ISBN: 9781303202704
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