Nature of magnetism in Co- and Mn-doped ZnO prepared by sol-gel technique

Abstract

Magnetic properties of sol-gel-prepared bulk samples of Co0.05Zn0.95O and Mn0.05Zn0.95O are reported before and after annealing in 5%H2∕95%Ar at 573 K for 6 h. The as-prepared samples are paramagnetic with the magnetic susceptibility χ following the Curie-Weiss law: χ=χ0+C∕(T−θ). The magnitudes of C are consistent with the magnetic moments expected for the Co2+ and Mn2+ states. After hydrogenation, the magnetism of Mn∕ZnO is unchanged but Co∕ZnO acquires room-temperature ferromagnetism (RTFM) with a magnetic moment of 0.35μB∕Co site and hysteresis loop with coercivity Hc≃600Oe, remanence Mr≃0.45emu∕g, and saturation magnetization Ms≃1.2emu∕g. Electron magnetic-resonance spectroscopy at 9.28 GHz gives signals corresponding to the Co2+ and Mn2+ states for the paramagnetic states and a broad FM signal for the hydrogenated Co∕ZnO. This difference under hydrogenation between Co∕ZnO and Mn∕ZnO suggests that n-type doping leads to stabilizing of RTFM in Co∕ZnO but not in Mn∕ZnO, the latter perhaps requiring p-type doping.

Study of room temperature ferromagnetism for cobalt and manganese doped ZnO diluted magnetic semiconductor

“…The Saturation magnetization (M s ) becomes more than three fold (table 1) and coercivity also increases remarkably upon hydrogenation ( figure 5). This is in agreement with the reports that hydrogenation causes a robust increase in Co doped ZnO [14,15]. Firstly, the FM ordering is found to be significantly higher for the Co+Mn doped sample than that for the pure Co doped sample.…”

“…behaviour at RT [13][14][15]. RTFM in a ZnO:Co system has, however, been reported when the samples were either co-doped with CuO [13] or hydrogenated [14,15]. The observed RTFM in hydrogenated samples was attributed either to the appearance of Co clusters [14] or oxygen vacancies [15].…”

“…RTFM in a ZnO:Co system has, however, been reported when the samples were either co-doped with CuO [13] or hydrogenated [14,15]. The observed RTFM in hydrogenated samples was attributed either to the appearance of Co clusters [14] or oxygen vacancies [15]. We have studied electronic and magnetic properties of single phase polycrystalline ZnCoO and ZnCoMnO samples with 5% Co and 2% Mn concentration, before and after hydrogenation.…”

“…In the case of polycrystalline bulk samples, prepared by the solid-state reaction method, many groups have reported paramagnetic (PM) * To whom any correspondence should be addressed. behaviour at RT [13][14][15]. RTFM in a ZnO:Co system has, however, been reported when the samples were either co-doped with CuO [13] or hydrogenated [14,15].…”

Manipulating coupling state and magnetism of Mn-doped ZnO nanocrystals by changing the coordination environment of Mn via hydrogen annealing

“…[19][20][21] In a hydrogen annealed Mndoped ZnO system, the magnetic properties are different, and the source of the observed magnetism is still under intense debate. Manivannan et al [22] noted that the magnetism of Mndoped ZnO is unchanged after hydrogenation. Sharma and Varma [23] proposed that the RT ferromagnetism in their hydrogenated sample is generated from oxygen vacancies and Zn interstitials.…”