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 ∼3.3μ_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 ∼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)] ∝ H^2/3. The extrapolation of the AT line gives the spin-freezing temperature T_g(0) ≈ 3.29 K