Understanding bifurcations in FC–ZFC magnetization of dilutely Fe3+ doped CdS nanoparticles

•FC–ZFC bifurcation in Fe doped CdS nanoparticles.•The bifurcation percentage w.r.t. ZFC decreases with increase in particle density.•Increase in inter-particle dipolar interactions with particle density.

The bifurcation between field-cooled and zero-field-cooled curves in magnetization vs. temperature measurement has been investigated in Fe3+ doped CdS nanoparticles with different crystal structures (wurtzite and zinc-blende) and external magnetic fields. It has been found that the field-cooled and zero-field-cooled curves start bifurcating from ambient temperature in diluted (powder) samples irrespective of crystal structures. However, in the high density samples (prepared by pelletizing the powder samples at a pressure of ~200 MPa) the bifurcation is significantly reduced within entire temperature regime. We have shown that the observed bifurcation in diluted (powder) samples is neither a consequence of blocking of super-moments in nanoparticle systems nor the spin-glass type transition, rather dominated by temperature independent component of magnetic susceptibility.