Ferromagnetism in ZnCoO due to Hydrogen-Mediated Co–H–Co Complexes: How to Avoid the Formation of Co Metal Clusters?

Abstract

There have been many studies of ferromagnetism in ZnCoO, and the results have been controversial. Secondary phases, such as Co oxides and Co metal clusters, in ZnCoO are easily produced during treatment, but the formation conditions are not well understood. We fabricated samples under hydrogen-injection conditions at different heat-treatment temperatures and examined the conditions by using synchrotron X-ray analysis under which Co 3 O 4 appeared or was transformed into Co metal. We investigated the transforming process of the ferromagnetic origin from intrinsic to extrinsic nature via intermediate region competition by Co−H−Co and Co metal cluster and suggest conditions that induce ferromagnetic spin ordering in ZnCoO due to Co−H−Co complexes through hydrogen mediation.

Analysis of oxygen vacancy in Co-doped ZnO using the electron density distribution obtained using MEM

“…The crystallinity of ZnO can be greatly affected by lattice strain [ 25 ] or native defects such as V O [ 26 - 28 ] and interstitial zinc (Zn i ) [ 27 , 28 ]. The contribution of lattice strain (resulting from the Co-doping concentration) to differences in crystallinity was assumed to be negligible because all powder samples were post-annealed at both 300°C and 800°C [ 17 , 29 ], which would relieve any lattice strain. Co doping was thought to induce insignificant amounts of lattice strain that might result from a difference in ionic radii, because the ionic radius of Zn 2+ (74 pm) is similar to that of Co 2+ (72 pm) [ 30 ].…”

“…ZnO and Co-doped ZnO (Zn 1−x Co x O, x = 0.01, 0.05, 0.1) powder samples were fabricated by sol-gel methods [ 16 , 17 ]. Zinc acetate dihydrate (Sigma-Aldrich, St. Louis, MO, USA) and cobalt acetate tetrahydrate (Sigma-Aldrich, St. Louis, MO, USA), used as starting materials, were dissolved in 2-methoxyethanol (Sigma-Aldrich, St. Louis, MO, USA) and stabilized by monoethanolamine (Sigma-Aldrich, St. Louis, MO, USA).…”

Investigating the development of spurious magnetism in single crystalline BaTi0.95Fe0.05O3−δwith highδby local structural probes

“…During the course of our extended study of dilute magnetism in Fe-doped BaTiO 3 single crystal, it turned out to be extremely difficult to search for any small amounts of precipitated magnetic phases using conventional tools [28][29][30][31][32][33], because they are expected to be buried deep within the enormous volume of the 'nonmagnetic' bulk matrix. In fact, in the present case, simple lab-based techniques failed to indicate Fe-metal precipitation even though significant changes in overall crystal and chemical compositions were revealed.…”

A simple one step synthesis of magnetic-optical dual functional ZIF-8 in a sodalite phase for magnetically guided targeting bioimaging and drug delivery

“…The similar XRD patterns of DOX/Fe 3 O 4 @ZIF-8 and pure ZIF-8 indicate that the introduction of DOX and Fe 3 O 4 has no impact on the structural integrity of ZIF-8. 57,58 FTIR spectra shown in Fig. 4a was used to determine the presence of DOX and Fe 3 O 4 within the ZIF-8 matrix.…”