Universality in the Magnetic Response of Metamagnetic Metals
  We report in this paper, measurements of the nonlinear susceptibility \chi_sub3(T) in the metamagnetic heavy fermion (HF) compound UPt3. At high temperatures, \chi_sub3(T) < 0 and small. It turns positive for T less than 35K, forms a peak at T = 10K and then decreases to zero with further decreasing temperature. The peak in \chi_sub3 occurs at a temperature T3 roughly half of T1, the temperature of the maximum in the linear susceptibility. We present results on URu2Si2 and UPd2Al3 to show that this feature is common to other HF materials. A two level model to describe the metamagnetic transition, with separation between the levels being the only energy scale, captures all experimentally observed features. 
B.S. Shivaram, D.G. Hinks, M. B. Maple, M.A.deAndrade and P. Kumar
cond-mat.str-el