Three-dimensional (3D) Ising universality in magnets and critical indices at fluid–fluid phase transition

Abstract

Experimental data for critical exponents in some magnetic materials are compared with recent theoretical results on the three-dimensional (3D) Ising model, as derived by one of us (ZDZ) based on two conjectures [Z.D. Zhang, Conjectures on the exact solution of three-dimensional (3D) simple orthorhombic Ising lattices, Phil. Mag. 87 (2007), pp. 5309–5419]. It is found that critical exponents in some bulk magnetic materials indeed form a 3D Ising universality. Our attention is then focused on the critical indices at fluid–fluid phase transition. We suggest to use Zhang's exponent β = 3/8 to fit the experimental data over the wider asymptotic region near the critical point of a fluid–fluid phase transition. The 3D Ising universality should exist for critical indices in a certain class of magnets and at fluid–fluid phase transition.

Keywords:

• magnetically ordered materials
• fluid–fluid
• phase transitions
• order–disorder effects

PACS::

• 75.40.-s
• 75.40.Cx
• 75.50.Cc

Acknowledgments

This study has been supported by the National Natural Science Foundation of China (under grant numbers 50831006 and 10674139). NHM acknowledges on-going affiliation with the University of Antwerp (UA) plus partial financial support through BOF-NOI, made possible by Professors D. Lamoen and C. Van Alsenoy.