Origin of ferromagnetism in Fe- and Cu-codoped ZnO

Abstract

Fe- and Cu-codoped ZnO was previously reported as a room-temperature dilute magnetic semiconductor. We have investigated the origin of the ferromagnetism in Zn0.95−xFe0.05CuxO using the zero-field Fe57 nuclear magnetic resonance and neutron diffraction. These measurements reveal that some Fe ions of Zn0.95−xFe0.05CuxO form a secondary phase, ZnFe2O4. Detailed comparison of nuclear magnetic resonance spectra of Zn0.95−xFe0.05CuxO, bulk ZnFe2O4 with normal spinel structure, and nanocrystalline ZnFe2O4 with inverted spinel structure shows that the secondary phase possesses an inverted spinel structure and is ferrimagnetic at room temperature, while normal zinc ferrite is nonmagnetic. The ferromagnetism in Fe- and Cu-codoped ZnO stems from the secondary phase, while the majority of Fe ions substituted into the ZnO lattice appears to remain magnetically inert.

The Magnetic Properties of Zn<sub>0.98</sub>Fe<sub>0.02</sub>O with Additional Cu Doping

“…that the RT FM in this system is intrinsic, in accordance with the previous work [7]. It should be noted that, additional Cu doping has not induced obvious change in ferromagnetism of Zn-Fe-O system at 300 K, but rather caused a small increase in M only at 10 K. It means that additional Cu doping has a little effect on ferromagnetism of Zn-Fe-O system, but not very crucial as mentioned in [4].…”

“…It is deemed that additional Cu doping is essential to achieve RTFM in Fe-doped ZnO bulk samples [3]. Howerver, Shim et al found that the ferromagnetism in Feand Cu-codoped ZnO stems from the secondary phase ZnFe 2 O 4 [4].…”

Band gap tailoring and enhanced visible emission by two-step annealing in Zn0.94Cu0.04Cr0.02O nanocrystals

“…Impurity atoms also contribute to visible emission; e.g., green luminescence from Cu acceptors in ZnO [13]. Shim et al [14] prepared the Cu, Mn co-doped ZnO samples with ferromagnetic property at room temperature, but the results showed that the ferromagnetism originated from the secondary phase of Zn Mn 2 O 4 . Previous work reported on a study of the oxygen sensing properties of Cr doped (1 at.%) and undoped ZnO [15] fabricated by reactive RF co-sputtering.…”

Effects of different sintering atmosphere on the structure and properties of Cu-doped ZnO powders prepared by sol–gel method

“…So far, the most popular mechanisms of the magnetic ordering for the ZnO related materials are carrier mediated exchange [15], using the bound magnetic polaron model based on the defects such as oxygen vacancy and Zn interstitial [16]. At the same time, some groups have pointed out that the ferromagnetism might be caused by the secondary phase rather than the substitution of the TM ions into the Zn site [17]. Recent reports about the observation of the room temperature (RT) ferromagnetism in copper doped ZnO materials have attracted great interest by the scientific community.…”