Moment Of Co Research Articles

Doping effects in strontium hexaferrite: Theoretical and experimental analysis

Hexagonal ferrites based on SrFe12O19 (SFO) are vital materials in the field of permanent magnets, valued for their cost-effectiveness and reliable magnetic properties, making them a more affordable alternative to rare-earth permanent magnets. This study focuses on understanding the doping effects of commonly used elements in SFO system. DFT calculation results show that doping La or La-Co can enhance the phase stability of SFO, in which Co has a preference for the 4f1 sites of Fe. The total magnetic moment was observed to slightly decrease with La doping, whereas it exhibited an increasing trend with La-Co and La-Ca-Co co-doping and the largest increase of 6.5 % can be obtained in Sr2LaCaFe44Co4O76 (SLCFCO). The increase in the total magnetic moment is mainly attributed to the smaller antiferromagnetic moment of Co than that of Fe on 4f1 sites, as well as the reduction in the antiferromagnetic Fe moments at 4f1 and 4f2 sites. The total density of states indicates a transition from semiconductor behavior to a metallic character both in the La-Co and La-Ca-Co doped versions. The experimental results validate the theoretical predictions, confirming enhancements in magnetic performance. The saturation magnetization increased from 63.86 Am2/kg in SrFe11.7O19 (SFO) to 67.53 Am2/kg in Sr0.4La0.4Ca0.2Fe10.5Co0.5O19 composition. These findings provide a vital understanding of tuning the magnetic and electronic properties in doped SFO, which will enable the development of advanced applications in magnetic materials.

Electronic, magnetic and structural properties of CoFeVAl and CoFeV0.5Mn0.5Al

In this study, we present results of a comprehensive computational and experimental study of CoFeVAl and CoFeV0.5Mn0.5Al Heusler alloys. It is shown that while CoFeVAl exhibits a fairly large degree of spin polarization, this material is not half-metallic due to the presence of the vanadium spin-down states at the Fermi level. However, replacing 50% of vanadium with manganese results in a nearly half-metallic transition, largely due to the shift of the Fermi level towards occupied states. Moreover, the half-metallicity of CoFeV0.5Mn0.5Al is rather robust in a wide range of considered mechanical strain and under experimentally observed B2-type atomic disorder, thus making this alloy potentially suitable for practical spintronic applications. Both considered alloys exhibit ferromagnetic alignment at larger lattice constants, aside from a relatively small magnetic moment of vanadium which is anti-aligned with the magnetic moments of Co, Fe and Mn. We have synthesized both CoFeVAl and CoFeV0.5Mn0.5Al alloys in cubic structure with some structural disorder using arc melting and annealing. The structural and magnetic properties of the synthesized CoFeV0.5Mn0.5Al alloy are in good agreement with the theoretical calculations but vary slightly from the parent compound.

Effect of Cobalt on the Microstructure of Fe-B-Sn Amorphous Metallic Alloys

Fe78B15Sn7 and (Fe3Co1)78B15Sn7 amorphous metallic alloys were prepared using the method of planar flow casting. The amorphous nature of ribbons containing 7 at. % Sn was verified by X-ray diffraction. The resulting chemical composition was checked by flame atomic absorption spectroscopy and by mass spectrometry with inductively coupled plasma. The microstructure of the as-quenched metallic glasses was investigated by 57-Fe and 119-Sn Mössbauer spectrometry. The experiments were performed with transmission geometry at 300 K, 100 K, and 4.2 K, and in an external magnetic field of 6 T. The replacement of a quarter of the Fe by Co did not cause significant modifications of the hyperfine interactions in the 57-Fe nuclei. The observed minor variations in the local magnetic microstructure were attributed to alterations in the topological short-range order. However, the in-field 57-Fe Mössbauer spectra indicated a misalignment of the partial magnetic moments. On the other hand, the presence of Co considerably affected the local magnetic microstructure of the 119-Sn nuclei. This was probably due to the higher magnetic moment of Co, which induces transfer fields and polarization effects on the diamagnetic Sn atoms.

Atomic-Scale Description of the Magnetic TiN|FeCo Multilayers.

Motivated by the experimental findings of Wolff et al., we investigated the TiN|FeCo multilayers at the atomic scale. Four different models were employed to investigate the interface, considering both Fe and Co surface terminations of the FeCo compounds. The interface formation energy formalism was employed to study the thermodynamic stability of these models. The results show that an interface mediated by Co atoms is most likely to appear in the experiment. Also, the Fe surface termination is more viable than a Co surface termination. The magnetic moments of Co at the interface are 1.48 μB/atom, which denotes a decay compared to bulk (1.76 μB/atom). Besides, Ti acquires a very small induced magnetization of -0.05 μB/atom. Our proposed atomistic model of the TiN|FeCo multilayer system fits perfectly with the structure obtained in experiments, and it is a step forward in the theoretical-experimental design of wear-resistant coatings with outstanding magnetic and mechanical properties.

Magnetic properties and magnetocaloric effect of DyCo9Si4

Polycrystalline samples of DyCo9Si4 with the tetragonal LaFe9Si4-type structure have been synthesized by arc melting and high-temperature annealing. Results of the magnetization M and specific heat Cp measurements show the existence of two magnetic anomalies at TC = 40 K and Tm = 20 K. The transition at TC = 40 K is attributed to the ferromagnetic transition of the Co sublattice. The magnetic moments of Dy3+ appear to align gradually below TC, and almost fixed below Tm, at which a broad maximum in Cp has been observed. Field-dependent M at T = 2 K up to H = 7 T suggested that the magnetic moment of Dy3+ is coupled antiferromagnetically with those of Co, forming a ferrimagnetic structure. Magnetization measurements up to 50 T at low temperatures using a pulse magnet demonstrated a spin-flip transition around H = 20 T, above which the magnetic moments of Co and Dy are in parallel. The spin-flip transition becomes broad with increasing temperature but still remains at TC = 40 K, indicating a strong antiparallel coupling between Co and Dy moments even in the paramagnetic state. The magnetocaloric effect was evaluated from Cp and M, and also from the sample-temperature variation in the quasi-adiabatic process with the pulsed magnetic field. The maximum entropy change for the field change from 5 to 0 T was observed at around T = Tm with the value ΔS = 5 J/kg K. The maximum temperature of ΔS shifts to higher temperatures in high magnetic fields, resulting in the large value of ΔS = 24 J/kg K at T ∼ TC by the field change from 50 to 0 T. The present results demonstrate that the pulsed-field measurement is a powerful method to evaluate the magnetocaloric effect of materials.

Anomalous Nernst effect and thermal conductivity in Co3Sn2S2 polycrystals

A polycrystalline sample of Co3Sn2S2 shandite was synthesized using spark plasma sintering for its densification. The unit cell parameters, a = 5.3688(1) Å and c = 13.1797(1) Å, refined from room temperature X-ray diffraction data, confirm the R-3m shandite structure. The frustrated nature of the Co magnetic network is invoked to explain the low effective paramagnetic moment of Co, μeff = 1.04μB/Co, whereas the ferromagnetic Curie temperature, TC = 175K, determined from T-dependent magnetic susceptibility corresponds to the metal to metal transition at that temperature. Interestingly, the residual resistivity ratio and resistivity values indicate that the electronic transport is driven by the in-plane contribution. This behaviour close to that of ab-plane transport of Co3Sn2S2 crystal fits well with the measurement of an anomalous Nernst effect (ANE). The latter reaches at T = 100K a maximum value Sxy = +1.5 μV K−1, i.e. a reduction by a factor of ≈2 as compared to crystal, explained by the reduction for the magnetization, M, of the former. This is also demonstrated by the H-dependent Sxy and M loops that match very well. Similarly, a hysteresis is found for the thermal conductivity demonstrating the existence of an anomalous thermal Hall effect of about 5 % of the total thermal conductivity. This study shows that ANE can be also measured in ceramics of Weyl ferromagnets.

Research progress of magnetic anisotropy enhancement mechanism of high-performance La-Co co-substituted M-type permanent magnet ferrites

<sec>La-Co co-substituted M-type ferrite, which was first reported at the end of the 20th century, as the cornerstone of high-performance permanent magnet ferrites, has received increasing attention from researchers around the world. The unquenched orbital moments of Co<sup>2+</sup> play a pivotal role in enhancing the uniaxial anisotropy of M-type ferrites. However, a comprehensive understanding of its microscopic mechanism remains elusive. In order to meet the increasing performance requirements of ferrite materials, it is imperative to clarify the mechanism behind the enhancement of magnetic anisotropy, and at the same time seek the guiding principles that are helpful to develop high-performance product quickly and economically. But its mechanism at a microscopic level has not been explained. This review comprehensively analyzes various studies aiming at pinpointing the crystal sites of Co substitution within the lattice. These investigations including neutron diffraction, nuclear magnetic resonance, and Mössbauer spectroscopy can reveal the fundamental origins behind the enhancement of magnetic anisotropy, thereby providing valuable insights for material design strategies aiming at further enhancing the magnetic properties of permanent magnet ferrites.</sec><sec>The exploration of co-substitution sites has yielded noteworthy findings. Through careful examination and analysis, researchers have discovered the complex interplay between Co ions and the lattice structure, revealing the mechanisms of enhanced magnetic anisotropy. The current mainstream view is that Co ions tend to occupy more than one site, namely the 4<i>f</i><sub>1</sub>, 12<i>k</i>, and 2<i>a</i> sites, all of which are located within the spinel lattice. However, there have also been differing viewpoints, implying that further exploration is needed to uncover the primary controlling factors influencing Co occupancy. It is worth noting that the identification of specific Co substitution sites, especially the spin-down tetrahedron 4<i>f</i><sub>1</sub>, has achieved targeted modifications, ultimately fine-tuning the magnetic properties with remarkable precision.</sec><sec>Furthermore, the reviewed research emphasizes the pivotal role of crystallographic engineering in tailoring the magnetic characteristics of ferrite materials. By strategically manipulating Co substitution, researchers have utilized the intrinsic properties of the lattice to amplify magnetic anisotropy, thereby unlocking new avenues for the advancement of permanent magnet ferrites.</sec><sec>In conclusion, the collective findings outlined in this review herald a promising trajectory for the field of permanent magnet ferrites. With a detailed understanding of Co-substitution mechanisms, researchers are preparing to open up new avenues for developing next-generation ferrite materials with enhanced magnetic properties.</sec>

Measurement of the Induced Magnetic Polarisation of Rotated-Domain Graphene Grown on Co Film with Polarised Neutron Reflectivity.

In this paper, we determine the magnetic moment induced in graphene when grown on a cobalt film using polarised neutron reflectivity (PNR). A magnetic signal in the graphene was detected by X-ray magnetic circular dichroism (XMCD) spectra at the C K-edge. From the XMCD sum rules an estimated magnetic moment of 0.3 μB/C atom, while a more accurate estimation of 0.49 μB/C atom was obtained by carrying out a PNR measurement at 300 K. The results indicate that the higher magnetic moment in Co is counterbalanced by the larger lattice mismatch between the Co-C (1.6%) and the slightly longer bond length, inducing a magnetic moment in graphene that is similar to that reported in Ni/graphene heterostructures.

Valence electron structures and thermal and magnetic properties of RCo5 (R=light rare earth) intermetallic compounds with medium- and high-entropy design at R site

RCo5-type (R=light rare earth) medium- and high-entropy intermetallic compounds, which are designed by random occupation of equiatomic multiple rare earth elements at the rare earth site, are prepared by arc melting and vacuum heat-treatment technologies, and their crystal structures and magnetic properties are studied by X-ray diffraction and magnetic measurements. The empirical electron theory of solids and molecules is used to investigate their valence electron structures, thermal and magnetic properties. The theoretical bond lengths and magnetic moments match the experimental ones well. The study reveals that the thermal and magnetic properties are strongly related to the valence electron structures modulated by medium- and high-entropy design at rare earth. The medium and high entropized designs induce the increase of the covalence electron numbers nc. It is helpful for stabilizing the crystal structure. The number of covalence electron pair of the strongest R-CoI bond affects the melting point. The magnetic moments of RCo5-type medium- and high-entropy intermetallic compounds, which mainly originate from the 3d magnetic electrons of Co atoms, are modulated by medium and high entropized rare earth due to their exchange interactions. The magnetic moment of Co at the 2c site is larger than that of Co at the 3g site, which is due to the electron transformations from magnetic to covalence electron for bonding with the rare earth at the 3g site. Curie temperatures raise with the increasing 3d magnetic electron numbers of Co atom.

Control of Compensation Temperature in CoGd Films through Hydrogen and Oxygen Migration under Gate Voltage.

Electrical control of magnetic properties is crucial for low-energy memory and logic spintronic devices. We find that the magnetic properties of ferrimagnetic CoGd can be altered through ionic liquid gating. Gate voltages manipulate the opposite magnetic moments in Co and Gd sublattices and induce a giant magnetic compensation temperature change of more than 200 K in Pt/CoGd/Pt heterostructures. The electrically controlled dominant magnetic sublattice allows voltage-induced magnetization switching. Both experiments and theoretical calculations demonstrate that the significant modulations of compensation temperature are relevant to the reduced Gd moments due to the presence of hydrogen ions at positive voltages as well as the enhanced Co moments and reduced Gd moments due to the injection of oxygen ions at negative voltages. These findings expand the possibilities for all-electric and reversible magnetization control in the field of spintronics.

Effect of Co substitution on ferrimagnetic Heusler compound Mn3Ga

Effect of Co substitution on Mn3Ga is investigated using first-principles study for structural and magnetic properties. Without Co, ferrimagnetic Heusler compound Mn3Ga is in tetragonal phase. With Co substitution, depending on Co concentration (x), Mn3Ga prefers tetragonal (cubic) phase when x≤0.5 (x≥0.5). Ferrimagnetism is robust regardless of x in both phases. While magnetic moments of two Mn do not vary significantly with x, magnetic moments of Co in two phases exhibit different behaviors, leading to distinct features in absolute value of total magnetic moment (|Mtot|). When x≤0.5, in tetragonal phase, magnetic moment of Co is vanishingly small, resulting in a decrease of |Mtot| with x. In contrast, when x≥0.5, in cubic phase, magnetic moment of Co is roughly 1 μB, which is responsible for the increase of |Mtot|. Electronic structure is analyzed with partial density of states for various x. To elucidate the counterintuitively small Co moment, the magnetic exchange interaction is investigated, where exchange coefficient between Co and Mn(II) in x≤0.5 is much smaller than that in x≥0.5.

Cold Ion-Molecule Chemistry: The Very Different Reactions of He⁺ with CO and NO.

The ion-molecule reactions He+ + CO → He + C+ + O and He+ + NO → He + N+ + O have been measured at collision energies between 0 and kB · 10 K. Strong variations of the rate coefficients are observed below kB · 5 K. The rate of the He+ + CO reaction decreases by ~30% whereas that of the He+ + NO reaction increases by a factor of ~1.5. These observations are interpreted in the realm of an adiabatic-channel capture model as arising from interactions between the ion charge and the dipole and quadrupole moments of CO and NO. We show that the different low-energy behavior of these reactions originates from the closed- vs. open-shell electronic structures of CO and NO.

Temperature Variation of Gilbert Damping Constant in 3d Transition Metals from First Principles

A theoretical investigation of temperature-dependent Gilbert damping is presented. We evaluate the Gilbert damping constant α (and the corresponding Landau frequency λ) at a finite temperature for hcp-Co, fcc-Ni, and Cu-doped fcc-Ni from first principles by combining the torque correlation model and the disordered local moment scheme, in which the finite-temperature effect is included as the transverse spin fluctuation. The calculated λ has, from the viewpoint of the material dependence, well reproduced the experimental results, but quantitatively, these values are more underestimated than the experimental values. A comparison with the lifetime approximation results reveals that a change in the electronic structure due to the spin fluctuation affects λ for Co and Ni but not for Fe. On the basis of the variation of the local magnetic moment of Co and Ni at finite temperature, we conclude that these differences in λ are due to the difference in the degree of itinerancy of spins.

Cold molecular gas outflow encasing the ionized one in the Seyfert galaxy NGC 3281

ABSTRACT We present ALMA CO (2-1) observations of the Seyfert 2 galaxy NGC 3281 at ∼100 pc spatial resolution. This galaxy was previously known to present a bi-conical ionized gas outflow extending to 2 kpc from the nucleus. The analysis of the CO moment and channel maps, as well as kinematic modelling, reveals two main components in the molecular gas: one rotating in the galaxy plane and another outflowing and extending up to ∼1.8–2.6 kpc from the nucleus, partially encasing the ionized component. The mass of the outflowing molecular gas component is Mmol, out = (2.5 ± 1.6) × 106 $\rm {{\rm M}_{\odot }}$ , representing ∼1.7–2 per cent of the total molecular gas seen in emission within the inner 2.3 kpc. The corresponding mass outflow rate and power are $\dot{M}_{\mathrm{out},\mathrm{mol}}$ = 0.12–0.72 $\rm {{\rm M}_{\odot }\, yr^{-1}}$ and $\dot{E}_{\mathrm{out},\mathrm{mol}}$ = (0.045–1.6) ${\times }\, 10^{40}$ $\rm {erg\, s^{-1}}$ , which translates to a kinetic coupling efficiency with the AGN power of only 10−4–0.02 per cent. This value reaches up to 0.1 per cent when including both the feedback in the ionized and molecular gas, as well as considering that only part of the energy couples kinetically with the gas. Some of the non-rotating CO emission can also be attributed to inflow in the galaxy plane towards the nucleus. The similarity of the CO outflow – encasing the ionized gas one and the X-ray emission – to those seen in other sources, suggests that this may be a common property of galactic outflows.

Magnetic optimization and regulation mechanism of La2CoMnO6 double-perovskite ceramics by Ti-doping at Mn-site

This work focuses on the magnetic optimization of La2CoMnO6 (LCMO) double-perovskite ceramics by Ti-doping at Mn-site. LCMO ceramics with different Ti-doping contents (LCMTxO, x = 0.1–0.4) were prepared by plasma activated sintering, and the effect of Ti-doping on the structural and magnetic properties of the ceramics is studied systematically. All the ceramics exhibit dense structure and small grain size, with a monoclinic P21/n crystalline structure. With the increasing of Ti-doping content, the proportions of Co2+ and Mn4+ in the LCMTxO ceramics change accordingly, reaching the highest values at x = 0.1. Since the Co2+-O-Mn4+ ferromagnetic super-exchange is the dominant factor affecting the magnetic properties of the LCMTxO ceramics, it is reasonable that a high saturation magnetization (Ms = 4.58μB/f.u) is obtained for the LCMT0.1O ceramic. The effect of Ti-doping on the orbital structure and magnetic regulation of the LCMTxO double-perovskite ceramics is further investigated by the first-principle calculation. It is found that the magnetic moments of Co and Mn ions will increase by the appropriate addition of Ti, which makes most Co ions exist in the form of Co2+, underpinning the La2Co2+Mn4+O6 ferromagnetic state and improving the magnetic properties.

The internal magnetic field in a ferromagnetic compound Y2Co12P7

The internal magnetic field in a ferromagnetic compound, Y2Co12P7 with T C = 150 K, was studied with µ +SR using a powder sample down to 2 K. The wTF-µ +SR measurements revealed the presence of a sharp magnetic transition at T C = 151 K, and the ZF-µ +SR measurements clarified the formation of static magnetic order below T C. The presence of two muon spin precession signals in the ZF-µ +SR spectrum below T C indicates the existence of the two different muon sites in the lattice. By considering the muon sites and local spin densities at the muon sites predicted with DFT calculations, the ordered magnetic moments of Co were successfully determined.

Half-metallic ferromagnetism in new quaternary Heusler alloys CoX’YP (X’ = Cr and Fe)

ABSTRACT In this study, we investigated the structural, electronic and magnetic properties of new quaternary Heusler alloys CoX'YP (X’ = Cr and Fe) using the accurate full-potential linearised augmented plane waves with local orbitals (FP-LAPW + lo) under the framework of the density functional theory (DFT) and the WIEN2k package. The generalised gradient approximation (GGA) is chosen to treat the exchange–correlation (XC) energy. The structural properties of the presented alloys are investigated in order to determine their structural parameters at equilibrium, such as: the lattice constant (a0 ), the bulk modulus (B0 ) and its first pressure derivative (B’). The structural stability of the CoCrYP and CoFeYP alloys is found in Y-type (I) structure, while their magnetic stability is reported in ferromagnetic phase. The electronic properties of the studied materials show the complete half-metallic character. The magnetic properties reveal that the total magnetic moment of the two alloys is found in integer value, obeying the Slater-Pauling rule. Furthermore, the calculated local magnetic moments of Co and X’ atoms are found with opposite signs, confirming the ferrimagnetic coupling within these compounds. According to the electronic and magnetic results found in this approach, we conclude that the compounds CoCrYP and CoFeYP are full half-metallic ferromagnetic materials.

First-principles study to probe the effect of substitution at X and Z sites on the electronic, magnetic and transport properties of Co2X(V, Nb, Ta)Z(Al, Ga, In, Si, Ge, Sn) Heusler alloys

In the present work, we have used density functional theory based electronic structure calculations to probe the role of isovalent substitution at X@(0.5, 0.5, 0.5) and Z@(0, 0, 0) site of Co2X(= Ta, Nb, V)Z(= Al, Ga, In). Further, we probed the role of electron-rich substitution at Z site on the electronic, magnetic and transport properties of half-metallic(HM) Co2TaZ( = Al,Ga,In) full Heusler alloys(FHA). One of our main aims is to study the effect of electron-rich substitution at Z site on the total and partial moments of X and Z sites. We have used the modified Becke–Johnson(mBJ) exchange–correlation term to calculate the HM band-gap. We observe that, isovalent substitution at X and Z sites provides a way to tune the lattice constant in range of ∼5.75 Å to ∼6.16 Å with sustained HM character. Further, it is noticed that the HM band-gap decreases with isovalent substitution (with low atomic number) at X site with maximum and minimum values of 1.09 eV and 0.5 eV, respectively. Isovalent substitution does not affect the total magnetic moment, however, it affects the atomic magnetic moment values. Further, we observe that 25% of substitution of tetravalent atoms (Si, Ge, Sn) at atomic site Z (having Al, Ga, In) enhances the total magnetic moment with a small decrease in the minority band-gap. However, 75 to 100 % of substitutions destroy the half-metallicity, showing an enhancement in the magnetic moment. Temperature dependent spin Seebeck coefficients corresponding to the 25% and 75% of substitution of tetravalent element at Z site exhibit values close to 150 μV/K and 25–75 μV/K, respectively, for temperatures above 400 K. Interestingly, electron rich substitution at Z cite, changes the orientation of the magnetic moment corresponding to the X (Ta) site element. In order to understand in detail the impact of substitution on the local magnetic moment of Co and X site atoms (V, Nb, Ta), we have performed calculations of respective X-ray magnetic circular dichroism(XMCD) spectra and analyzed the results in terms of unoccupied density of states. XMCD spectra of L2,3 edges of Co atom show only small deviation (in the intensity) with the changes in the X and Z sites. Unlike the case of Co atom, we find that the XMCD spectra of M2,3 edges of Ta atom exhibit substantial changes when tetravalent atoms replace the trivalent atoms at the Z site.

Effects of the charge–dipole and charge–quadrupole interactions on the He+ + CO reaction rate coefficients at low collision energies

The reaction between He+ and CO forming He + C+ + O has been studied at collision energies in the range between 0 and k B ⋅ 25 K. These low collision energies are reached by measuring the reaction within the orbit of a Rydberg electron after merging a beam of He(n) Rydberg atoms and a supersonic beam of CO molecules with a rotational temperature of 6.5 K. The capture rate of the reaction drops by about 30% at collision energies below k B ⋅ 5 K. This behavior is analyzed in terms of the long-range charge–dipole and charge–quadrupole interactions using an adiabatic-channel capture model. Although the charge–dipole interaction has an effect on the magnitude of the rate coefficients, the effects of the charge–quadrupole interaction determine the main trend of the collision-energy dependence of the rate coefficients at low collision energies. The drop of the capture rate coefficient at low collision energies is attributed to the negative sign of the quadrupole moment of CO (Q zz = −2.839 D Å) and is caused by the |JM⟩ = |00⟩ and |1 ± 1⟩ rotational states of CO, which represent about 70% of the CO molecules at the rotational temperature of 6.5 K.

Effects of surface polarity on the structure and magnetic properties of Co implanted polar ZnO wafers

Microstructural and magnetic properties of ion implantation method prepared Co doped Zn polar and O polar ZnO wafers are investigated by a combined experimental and theoretical approach. Substantial intrinsic ferromagnetism is observed in all the doped ZnO wafers. The ferromagnetism of Co implanted oxygen polar ZnO wafer is found to be larger than that of zinc polar ZnO. First principle calculations reveal that the magnetic moments mainly come from the Co-3d and O-2p states. The O-2p state has a stronger hybridization with the Co-3d state in oxygen polar ZnO, resulting in higher magnetic moments of Co implanted oxygen polar ZnO. These results not only benefit to a better understanding of the origin of surface-polarity dependent ferromagnetism in ZnO diluted magnetic semiconductors but also may open up the possibility to employ these polar ZnO in spintronic devices.