| Summary: | 博士 === 國立臺灣大學 === 物理學系研究所 === 86 === Hysteresis and switching properties of the single domain particles were stu
died based on the coherent rotation model. Effects of textural distri
bution under thermal agitation, the limited step Monte Carlo method and
dipolar interaction has been taken into Account.
For the effects of textural distri
bution, we found that effects of mis-orientation of easy axes q_K contrib
utes prominently to the energy barrier height and coercivity variation whe
n the system is less sensitive to thermal agitation, whilst particles' volume
V distribution becomes more important if the system is more sensit
ive to thermal agitation. The most important factor which causes the
spreading of switching field distribution is due mainly to the particl
e's volume distribution, and the mean square root of the particle volum
e is the characteristic value of the system if it has a widely log normal dis
tribution in volume. Distribution of anisotropy constant K is most influenti
al to contribute to coercivity and energy barrier height variation regardless
of thermal agitation. But in a typical physical system the distribution i
n K is very narrow indeed, so we see that the textural effect of K is much l
ess important than that of q_K and V.
In addition, the Metropolis Monte Carlo scheme with limited s
teps can be employed to simulate the magnetization reversal behavior with
good results. However, the method should be carried out with a suitab
le step length at high frequency and a relatively large value in KV/kT.
In the presence of
dipolar interaction between magnetic particles we find that reduction in magn
etic remanence is practically negligible, the switching field distribution s
pread out and coercivity reduced by such interaction, and the effects of dipo
lar interaction was obscured from the disordered distribution in the easy axe
s.
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