This thesis presents the results from Monte Carlo calculations on classical vector spins in
face-centered-cubic (FCC) lattices. The goal of the study was to understand the effect of
interlayer coupling, dilution of magnetic atoms in the lattice, and symmetry-changing
strain.
Experimental work by T. M. Giebultowicz et al. and J. A. Borchers et al. greatly inspired
my work [1, 2]. J. A. Borchers's group studied NiO/CoO superlattices and observed that
the magnetic order of CoO persisted above its Neel temperature due to the effect of
interlayer coupling with NiO, which has a higher Neel temperature than CoO [1].
Simulating on a model of NiO/CoO bilayer reproduced the experimental results from
Borchers et al. [1]. I concluded that exchange pinning on the NiO/CoO interface
preserves the magnetic order of CoO above its Neel temperature significantly.
Building on this initial result, a ferromagnet/antiferromagnet/ferromagnet (FM/AFM/FM)
trilayer model was studied, where the ferromagnetic (FM) layers were
antiferromagnetically coupled. First, I calculated the strength of the AF coupling as a
function of the number of antiferromagnetic (AFM) spacer monolayers and concluded
that the strength of AFM coupling decreases as the number of AFM spacer monolayers
increases.
Secondly, I added a uniaxial anisotropy to the model and obtained magnetization curves
which exhibited hysteresis-like features with an external field and a first order magnetic
transition. Lastly, I diluted the AFM spacer layer in the FM/AFM/FM trilayer by
replacing magnetic spins with zero spins in the model. The dilution of AFM spacer layer
caused fluctuations in the magnetization curves with external field but the strength of
AFM coupling decreases as the number of AFM monolayers increases as in the nondiluted
cases.
The experimental results from T.M. Giebultowicz's group on MnSe/ZnTe superlattices
by neutron scattering showed incommensurate helical spin order in MnSe, where MnSe
layers were under tensile strain due to a small mismatching in the lattice parameter [2]. In
addition, they observed that the pitch of the spin helix increased as the temperature
increased [2]. I modeled the MnSe/ ZnTe system with Monte Carlo method and found
that the pitch of the spin helix increased with temperature. In fact, the dependence of
helix pitch on temperature was present regardless of the thickness of the sample, so I
concluded that this pitch increase is not from the weakening of coupling of surface spins / Graduation date: 2013 / Access restricted to the OSU Community at author's request from Jan. 18, 2013 - July 18, 2013
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/36203 |
| Date | 18 July 2013 |
| Creators | Park, Seongweon |
| Contributors | Giebultowicz, Tomasz, Schneider, Guenter |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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