JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, vol.26, no.11, pp.3257-3262, 2013 (SCI-Expanded)
In this work, we report on the DC magnetic properties of Ho doped ZnO, Zn0.8-4x Ho x O y (0.05≤x≤0.10), polycrystalline samples prepared by the so-called solid state reaction method. Magnetic measurements, M-H and M-T, done by using a PPMS magnetometer, show a paramagnetic behavior including indirect antiferromagnetic coupling between some Ho3+ magnetic moments. In other words, the negative values of the Curie-Weiss temperatures, θ, for the polycrystalline samples with six different Ho concentrations indicate that there is an effective antiferromagnetic coupling among the magnetic moments of Ho3+ ions. However, the decrease in the magnitude of θ with increasing x indicates that this coupling decreases with increasing amount of Ho in the compounds. Furthermore, the effective magnetic moments, μ eff, per Ho atom calculated from the 1/χ-T curves gradually increase with increasing concentration. Therefore, the trends of the magnitudes of θ, and μ eff values clearly indicate that apart from the antiferromagnetic coupling there is also an increasing contribution of a ferromagnetic coupling with increasing x. Hence, one may also conclude that the compounds studied seem to have a kind of spin-glass behavior.