Study of superparamagnetic clusters in Co²⁺-exchanged NaY zeolite

Abstract

Magnetic properties of Co²⁺-exchanged NaY zeolite have been investigated using a dc magnetization technique. In the presence of low applied magnetic fields, a difference between zero-field-cooled and field-cooled magnetizations is observed below ∼3.4K. At T > 5 K, the M vs H∕T curves superimpose and these curves could be fitted well using the Langevin function, which yields a saturation moment of 3.2μ_B per Co²⁺ ion and a cluster moment of 6.66μ_B. This indicates that there are superparamagnetic clusters which are formed due to a positive exchange coupling among the Co²⁺ ions. For T < 5 K, the M vs H∕T curves do not superimpose on the curves for T > 5 K. The analysis of the low-temperature M vs H data suggests the building up of weak antiferromagnetic-type correlation between the superparamagnetic clusters at T < 5 K.