Local structure and magnetism of Co3+ in wurtzite Co:ZnO

Abstract

The structural and magnetic properties of 30% and 50% Co-doped ZnO have been investigated in order to determine the influence of the presence of Co 3+ as a potential p-type dopant. For 30% doping, Co 3+ could be stabilized in the wurtzite lattice of ZnO without phase separation by providing high oxygen partial pressures during growth. At 50% Co concentration, the crystal lattice destabilizes. X-ray absorption spectroscopy and simulations are used to substantiate the valence and local structure of Co 3+ . Integral and element selective magnetometry reveals uncompensated antiferromagnetism of the Co atoms irrespective of being present as Co 2+ or Co 3+ .

Unravelling the Elusive Antiferromagnetic Order in Wurtzite and Zinc Blende CoO Polymorph Nanoparticles

“…Interestingly, there is no sign of metallic Co neither in the X‐ray absorption spectroscopy (XAS) (not shown) nor in the XMCD, indicating the magnetic signal arises from the oxides. In fact, simulations of the XMCD results indicate that the signal arises predominantly from Co 2+ ions in tetrahedral positions, as expected for wurtzite and zinc blende‐CoO (see Figure S3 in the Supporting Information) . Moreover, the XMCD signal at 300 K is considerable weaker than at low temperatures, where the magnetic moment (roughly proportional to the area of the XMCD spectra) decreases a factor 100 from 15 to 300 K (Figure , inset), in full agreement with the temperature dependence of M S , hence, corroborating the uncompensated spins as the origin of the ferromagnetic‐like behavior in the samples.…”

“…The antiferromagnetic order obtained for both wurtzite‐CoO and zinc blende‐CoO is consistent with the theoretical predictions, although for wurtzite‐CoO the magnetic order is far more complex than theoretically proposed. Interestingly, the results on wurtzite‐CoO are also consistent with single crystalline wurtzite Zn 1− x Co x O films with large Co contents ( x = 0.6), which show an antiferromagnetic order with uncompensated spins …”

Enantiomeric resolution and X-ray optical activity of a tricobalt extended metal atom chain

“… 12 This can be compared to more common situations where high-spin divalent cobalt atoms carry a spin magnetic moment of 3 μ B with some additional orbital magnetic moment. 7b , 20 When comparing with previous Co K-edge XMCD data from literature, e.g. Co 2+ ions in a ZnO crystal, a simple cross-multiplication suggests that the expected intensity for XMCD in sample 2 cannot be larger than 2 × 10 –4 of the XAS spectra.…”

Transition from a hysteresis-like to an exchange-bias-like response of an uncompensated antiferromagnet

“…The 30% and 50% samples have been sputtered using metallic targets of Co and Zn at a Ar : O 2 ratio of 10 : 1 standard cubic centimeter per minute (sccm), a sputter power of 20 W, and a substrate temperature of 450 • C (30%) and 294 • C (50%). These parameters yield an optimized crystalline quality [32]. The film containing 60% Co has been sputtered from a ZnO and Co 3 O 4 ceramic composite target with a 3:2 ratio using only Ar as sputter gas, a sputter power of 30 W, and a substrate temperature of 525 • C [33].…”

“…The size of the hysteresis opening and the vertical shift of the Co:ZnO M (H ) curve depends on the Co-doping concentration. Therefore, for this work samples of different Co-doping concentrations with ample precharacterization [25,29,32] are studied as a function of temperature and cooling field, using superconducting quantum interference device (SQUID) magnetometry.…”