The structural, optical and magnetic properties of Mn doped ZnO nanocrystalline particles, Zn1-xMnxO, with different percentages of Mn content have been studied. XRD and XPS measurements showed that all samples with Mn doping up to x = 0.1 possess typical wurtzite structure and have no other impurity phases. The incorporation of Mn ions into the ZnO lattice was also confirmed by FTIR and UV–Vis. spectroscopy results. Both XRD and SEM results indicated a slight decrease in the grain size with increasing the Mn doping level. The XPS results indicated an increase in the oxygen vacancies concentration with increasing the Mn doping level. The magnetization measurements revealed a weak ferromagnetic behavior at room temperature and a clear ferromagnetic behavior with relatively large coercive fields at low temperature. The ferromagnetic order is improved by increasing the Mn doping. In addition, we observed an increase in the concentration of oxygen vacancies, which is also induced by increasing the Mn doping level. A ferromagnetic coupling of the local moment of Mn dopants through the sp-d exchange interaction and oxygen vacancies, in addition to different magnetic contributions due to different forms of Mn ions that coexist in the Mn doped nanoparticles were presented in order to interpret the observed magnetic behavior. We observed a clear red shift in the direct band gap and an increase in the coercive field and saturation magnetization values with increasing the Mn doping level.

Influence of Mn doping on the magnetic and optical properties of ZnO nanocrystalline particles

Effects of Co concentration and annealing on the magnetic properties of Co-doped ZnO films: Role of oxygen vacancies on the ferromagnetic ordering

To establish intrinsic ferromagnetism (FM) and to detect its micro-structural origin (if any), sol–gel derived Zn0.95Mn0.05O films have been undergone low energy (800 keV) Ar4+ ion irradiation. The structural, optical, magnetic and micro-structural properties of irradiated and un-irradiated films were investigated by X-ray diffraction (XRD), UV-visible and photoluminescence (PL) spectroscopy, field and temperature dependent magnetization measurements, X-ray absorption near edge spectroscopy (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy. All the films exhibit single-phase wurtzite structure and intrinsic FM. The band gap and band tail parameters show systematic variation with fluence of irradiation. PL spectra exhibit a green emission peak (oxygen vacancy) and that has been suppressed significantly for the film with low fluence (5 × 1014 ions per cm2) of irradiation. The film irradiated with low fluence exhibits an absence of antiferromagnetic (AFM) interaction and the strongest FM. The studies of XANES and EXAFS indicate a difference in oxidation state and local environment for Mn in comparison to Zn in the host ZnO matrix. The film that exhibits strong FM also shows a comparatively higher number of tetrahedral coordinated Mn ions. The magnetic properties have been correlated with optical and micro-structural properties and low fluence of ion irradiation has been supposed to be optimized.

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Correlation between magnetic and micro-structural properties of low energy ion irradiated and un-irradiated Zn0.95Mn0.05O films

Effect of the oxygen deficiencies creation on the suppression of the diamagnetic behavior of SrTiO3 compound

Spin-orbit coupling (SOC) plays a crucial role in magnetic and electronic properties of $5d$ iridates. In this paper we have experimentally investigated the structural and physical properties of a series of Ir-based double perovskite compounds ${\mathrm{Pr}}_{2\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{MgIrO}}_{6}(x$ = 0, 0.5, 1; hereafter abbreviated as PMIO, PSMIO1505, and PSMIO). Interestingly, these compounds have recently been proposed to undergo a transition from the spin-orbit-coupled Mott insulating phase at $x=0$ to the elusive half-metallic antiferromagnetic (HMAFM) state with Sr doping at $x=1$. However, our detailed magnetic and electrical measurements refute any kind of HMAFM possibility in either of the doped samples. In addition, we establish that within these ${\mathrm{Pr}}_{2\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{MgIrO}}_{6}$ double perovskites, changes in Ir-oxidation states ($4+$ for PMIO to $5+$ for PSMIO via mixed $4+/5+$ for PSMIO1505) lead to markedly different magnetic behaviors. While SOC on Ir is at the root of the observed insulating behaviors for all three samples, the correlated magnetic properties of these three compounds develop entirely due to the contribution from local Ir moments. Additionally, the magnetic ${\mathrm{Pr}}^{3+}$ ($4{f}^{2}$) ions, instead of showing any kind of ordering, only contribute to the total paramagnetic moment. It is seen that the ${\mathrm{PrSrMgIrO}}_{6}$ sample does not order down to 2 K despite antiferromagnetic interactions. But, the ${d}^{5}$ iridate ${\mathrm{Pr}}_{2}{\mathrm{MgIrO}}_{6}$ shows a sharp antiferromagnetic (AFM) transition at around 14 K, and in the mixed valent ${\mathrm{Pr}}_{1.5}{\mathrm{Sr}}_{0.5}{\mathrm{MgIrO}}_{6}$ sample the AFM transition is shifted to a much lower temperature ($\ensuremath{\sim}6$ K) due to weakening of the AFM exchange.

Evolution of electronic and magnetic properties in a series of iridate double perovskites Pr 2 − x Sr x MgIrO 6 ( x = 0 , 0.5 , 1.0 )

Sol-gel derived thin films of Zn0.95Mn0.05O have been implanted with Ar9+ ions with doses viz. 5x10e14 ions/cm2 (low), 1x10e15 ions/cm2 (intermediate) and 1x10e16 ions/cm2 (high). Structural, morphological, optical and magnetic properties of the films have been investigated. Structural study confirmed single phase, wurtzite structure of the films. The absence of impurity phase has been confirmed from several measurements. Ion implantation induces a large concentration of point defects into the films as identified from optical study. All films exhibit well above room temperature (RT) intrinsic ferromagnetism (FM) as evidenced from field and temperature dependent magnetization measurements. The magnetization attains the maximum value for high dose of Ar9+ ion implanted film. It shows RT saturation magnetization (MS) value of 0.69emu/gm. The observed FM has been correlated with proportion of intrinsic defects, such as, zinc and oxygen vacancies and the values of MS. Defect induced formation of bound magnetic polaron actually controls the FM. The utility of these films in transparent spin electronic device has also been exhibited.

Correlation between defect and magnetism of Ar9+ implanted and un-implanted Zn0.95Mn0.05O thin films suitable for electronic application

We have investigated the structural and physical properties of double perovskite (DP) $\mathrm{La}A{\mathrm{VMoO}}_{6}$ ($A={\mathrm{Ca}}^{2+}$, ${\mathrm{Ba}}^{2+}$; abbreviated as LCVMO and LBVMO from now on) compounds, proposed to be possible half-metallic antiferromagnets (HMAFMs). Here we show that within $\mathrm{La}A{\mathrm{VMoO}}_{6}$ double perovskite structure, La-O covalency competes against $B$-site as well $A$-site cationic order and this competition critically influences their physical properties. Evidently, the presence of ${\mathrm{Ca}}^{2+}$ or ${\mathrm{Ba}}^{2+}$ at the $A$ site along with ${\mathrm{La}}^{3+}$ would offer a tool to modify the $A$-site ordering and consequently influence the La-O covalency as well. Our experimental results reveal that LCVMO lies at the extreme end of this family and accommodates large scale phase separation in terms of La, V, and Ca, Mo-rich phases as a result of dominant La-O covalency. On the other hand, LBVMO is more correctly described as a layered $A$-site ordered and nearly complete $B$-site disordered double perovskite where cationic order dominates the La-O covalency. The general trend of our experimental findings is in agreement with the ab initio electronic structure calculations, carried out on realistic structures based on local coordination obtained from extended x-ray-absorption fine-structure study.

Cationic order versus La-O covalency in LaA(Ca,Ba)VMoO6 double perovskites

Effect of Ni doping on the magnetic and electronic properties of half heusler Cu1-xNixMnSb alloys

Cubic half-Heusler Cu1-x Co x MnSb ([Formula: see text]) compounds have been investigated both experimentally and theoretically for their magnetic, transport and electronic properties in search of possible half metallic antiferromagnetism. The systems (Cu,Co)MnSb are of particular interest as the end member alloys CuMnSb and CoMnSb are semi metallic (SM) antiferromagnetic (AFM) and half metallic (HM) ferromagnetic (FM), respectively. Clearly, Co-doping at the Cu-site of CuMnSb introduces changes in the carrier concentration at the Fermi level that may lead to half metallic ground state but there remains a persistent controversy whether the AFM to FM transition occurs simultaneously. Our experimental results reveal that the AFM to FM magnetic transition occurs through a percolation mechanism where Co-substitution gradually suppresses the AFM phase and forces FM polarization around every dopant cobalt. As a result a mixed magnetic phase is realized within this composition range while a nearly HM band structure is developed already at the 10% Co-doping. Absence of T 2 dependence in the resistivity variation at low T-region serves as an indirect proof of opening up an energy gap at the Fermi surface in one of the spin channels. This is further corroborated by the ab initio electronic structure calculations that suggests that a nearly ferromagnetic half-metallic ground state is stabilized by Sb-p holes produced upon Co doping.

Development of half metallicity within mixed magnetic phase of Cu1−xCoxMnSb alloy

2 and 4 at% Mn doped ZnO samples were synthesized by sol‐gel technique. The structural, compositional and magnetic properties were investigated. The 4 at% Mn doped sample contains secondary phase of ZnMnO3. The compositions of the samples are close to perfection. Crystallite size decreases with increase in doping. Both samples indicate absence of ferromagnetism. Strong presence of antiferromagnetism was found and it falls with increasing Mn doping. Simultaneously paramagnetic fraction of spin increases.

S. K. Neogi

Papers

Correlation between defect and magnetism of Ar9+ implanted and un-implanted Zn0.95Mn0.05O thin films suitable for electronic application

Cationic order versus La-O covalency in LaA(Ca,Ba)VMoO6 double perovskites

Effect of Ni doping on the magnetic and electronic properties of half heusler Cu1-xNixMnSb alloys

Development of half metallicity within mixed magnetic phase of Cu1−xCoxMnSb alloy

Absence of Ferromagnetism in Mn Doped ZnO