2026-09-20T13:51:23Z https://www.ideals.illinois.edu/oai-pmh

oai:www.ideals.illinois.edu:2142/25248 2023-07-10 col_2142_8859 col_2142_5131 com_2142_8858 com_2142_234 com_2142_5130

Wortis, M. Cheung, Ho Fai 2011-06-03T14:49:32Z 2011-06-03T14:49:32Z 10000-01-01 1986 We give a brief survey of Ising spin systems in the presence of random bonds or random fields. Specific calculations are done on the twodimensional short-ranged random-bond model and the three-dimensional random-field model. The phenomenological renormalization group and the transfer-matrix method are generalized to random systems and applied to the random-bond Ising model, also called the Edwards-Anderson spin-glass model. Results show that the two-dimensional Edwards-Anderson model has a spin-glass transition at zero temperature, in agreement with other calculations. We obtain an accurate estimate of the correlation-length exponent. We also find unexpectedly different critical behavior for different bond distributions. A simple renormalization-group calculation is applied to the twodimensional random-bond Ising model with non-zero-mean bond strength. Our result fails to confirm McMillan's result that there are two different critical behaviors along the ferromagnetic phase boundary. McMillan's domain-wall renormalization group is applied to the three -dimensional random-field Ising model. Numerical results show that the critical behavior of this model is controlled by a fixed point at zero temperature. The exponents are estimated. We find that, whenever there is a relevant zero-temperature fixed point, the singular part of the free energy is not of the usual form: The leading exponent that describes the renormalization-group flow towards zero temperature is relevant to the critical behavior. One of the consequences is that the hyperscaling law is modified. This new picture explains many experimental results for dilute antiferromagnets, ·which are experimental realizations of the random-field Ising model. We also discuss the possibility of a first-order transition for this model. Submitted by Carolyn Mead (cmead2@illinois.edu) on 2011-06-03T14:49:32Z No. of bitstreams: 1 1986_cheung.pdf: 5828633 bytes, checksum: 8330fe5847af6f6cd298d62f9f433cc0 (MD5) Made available in DSpace on 2011-06-03T14:49:32Z (GMT). No. of bitstreams: 1 1986_cheung.pdf: 5828633 bytes, checksum: 8330fe5847af6f6cd298d62f9f433cc0 (MD5) Previous issue date: 1986 Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Carolyn Mead (cmead2@illinois.edu) on 2011-06-03T14:49:32Z Item is restricted indefinitely. Restriction data tranferred 2014-07-01T11:12:27-05:00 Original Data Group with Access UIUC Users [automated] Release Date: none Reason: Thesis Thesis U of I Only 999316 http://hdl.handle.net/2142/25248 en 1986 Ho Fai Cheung Ising spin systems random bonds random fields phenomenological renormalization transfer matrix Studies in random Ising spin systems Dissertation / Thesis text Physics Physics University of Illinois at Urbana-Champaign Dissertation Ph.D.