Magnetic properties of Ni2+ clusters in NaY zeolite

We have investigated the magnetic properties of Ni2+ exchanged NaY zeolite by using a direct current magnetization technique. At T>5 K, the M vs H/T curves superimpose and these curves could be fitted well using a Langevin function with a log-normal distribution of moments. The mean spin-cluster moment has been found to be similar to 3.3 mu(B). The deviation from the superposition of the M vs H/T curves is observed at T < 5 K indicating the building up of a spin-spin correlation between Ni clusters below 5 K. The zero-field-cooled and field-cooled magnetization curves show branching at low temperatures (T <= 5 K) under low applied magnetic fields (H <= 1 kOe) with a peak in the zero-field-cooled magnetization curves. A log-normal distribution of spin-freezing/blocking temperature has been observed with mean spin-freezing/blocking temperature similar to 3.0 K. The peak temperature T-g decreases with increasing field and follows the de Almeida-Thouless (AT) line [1-T-g(H)/T-g(0)]proportional to H-2/3. The extrapolation of the AT line gives the spin-freezing temperature T-g(0)approximate to 3.29 K. (c) 2007 American Institute of Physics.