## Yang Liu

I am currently working on three related projects with Professor Dahmen and other collaborators:

1) We are conducting numerical studies of the zero-temperature Gaussian random-field Ising model (zt-GRFIM) in both equilibrium and non-equilibrium. We compare the no-passing rule, mean-field exponents and universal quantities in 3D (avalanche critical exponents, fractal dimensions, scaling functions and anisotropy measures) for the equilibrium and non-equilibrium disorder-induced phase transitions. We show compelling evidence that the two transitions belong to the same universality class.

2) We are also conducting numerical studies of the ΔH(M,ΔM) method and its ability to accurately determine intrinsic switching field distributions in interacting granular magnetic materials such as perpendicular recording media. In particular, we study how this methodology fails for large ferromagnetic inter-granular interactions: the associated strongly correlated magnetization reversal cannot be properly represented by the ΔH(M,ΔM) method, which is based on a mean-field approximation.

3) Finally, we are now working on the deep connection between the non-equilibrium and equilibrium critical point of the RFIM. The key point is to introduce temperature fluctuations and a finite field-sweeping frequency Ω into the non-equilibrium RFIM. By tuning Ω and T, we can study the entire experimentally relevant crossover regime from the equilibrium to the non-equilibrium RFIM.

**Publications**

Y. Liu, K. Dahmen, and A. Berger, "Determination of intrinsic switching field distributions in perpendicular recording media: Numerical study of the ΔH(M,ΔM) method," *Physical Review B* **77 **,054422 (2008)

Y. Liu, K. Dahmen, and A. Berger, "A comparative study of the ΔH(M,ΔM) method reliability for square and

triangular lattices," *Journal of Applied Physics * **103**, 07F504 (2008)

Y. Liu and K. Dahmen, "No-passing rule in the ground state evolution of the random-field Ising model," *Physical Review E* **76**, 031106 (2007)

Y. Liu, K. Dahmen, and A. Berger, "The role of dipolar interactions for the determination of intrinsic switching field distributions," http://arxiv.org/abs/0803.1191

Y. Liu and K. Dahmen, "Random field Ising model in and out of equilibrium," http://arxiv.org/abs/cond-mat/0609609