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|Title:||Experimental Study of Tricritical Phenomena in the Metamagnet Ferrous-Chloride|
|Department / Program:||Physics|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Subject(s):||Physics, Condensed Matter|
|Abstract:||The magneto-optical rotation (theta)(,F) and heat capacity in constant applied field C(,H(,a)) have been simultaneously determined for the metamagnet FeCl(,2). Since (theta)(,F) is proportional to magnetization we are able, for the first time, to express both C(,H(,a)) and (theta)(,F) as functions of internal magnetic field along different isotherms.
Following a detailed description of our experimental system, data are reported which were taken in the vicinity of the tricritical point at T(,t) = 20.6K and in an applied field of H(,a) = 10.2kOe. Eight isotherms above the tricritical temperature T(,t) have been used to verify the tricritical scaling hypothesis. A scaling function for the magnetization is proposed, which is found to agree well with our experimental results. A scaling analysis of the heat capacity data is also shown to support the tricritical scaling hypothesis. Tricritical exponents extracted from this analysis are (alpha)(,t) = 0.65 (+OR-) 0.05, (phi) = 2. and (')(alpha) = -0.35 (+OR-) 0.05.
For temperatures below T(,t), light scattering and heat capacity C(,H(,a)) have been simultaneously determined, both quantities are found to show discontineous changes at the mixed-phase boundaries. A theory which explains the step discontinuity in heat capacity C(,H(,a)) is presented. The strong light scattering in the mixed-phase region has been used to determine the mixed-phase boundaries and result in the tricritical exponent (beta)(,(mu)) = 0.63 (+OR-) 0.05.
Tricritical exponents extracted from our data are found to be consistent with the scaling hypothesis and to satisfy the scaling laws, but to be in poor numerical agreement with mean-field predictions. We show that the agreement with theory can be improved by including logarithmic correction factors.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1980.
|Date Available in IDEALS:||2015-05-13|