Magnetic Ion Exchange Interactions in NiO–MgO Solid Solutions (original) (raw)
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Crystal field calculations of energy levels of the Ni2+ ions in MgO
Journal of Luminescence, 2013
The electronic energy levels of six-fold coordinated Ni 2 þ ion in magnesium oxide MgO were calculated using the exchange charge model of crystal field theory. The calculated energetic positions of the Ni 2 þ levels match well the experimental spectrum. Inclusion of the spin-orbit (SO) interaction is compulsory to account for the first excited 3 T 2g state fine structure; however, it does not explain why out of four levels arising from the 3 T 2g state, only two are seen in the experimental spectra. One possible explanation to this fact can be advanced by invoking the Jahn-Teller effect.
Magnetic behavior of Co and Ni implanted MgO
Journal of Magnetism and Magnetic Materials, 2004
Single crystals of MgO were implanted with high doses of Co and Ni ions, aiming at the possibility of producing colloidal dispersions of metallic precipitates. Post-implantation annealing in vacuum is used to promote the diffusion of the implanted ions and the recovery of the MgO lattice. Results of magnetization measurements as a function of temperature and magnetic field are presented and correlated with information obtained by Rutherford backscattering measurements in the same samples.
Magnetic susceptibilities of Co- and Ni-doped MgO
Journal of Physics: Condensed Matter, 1992
The temperature dependence (1.7-3W K) of the Dc magnetic suseeplibililies x for the syxtems M,Mgl-,O @=CO, Ni) with , p < pF (where ps 0.14 is the percolation threshold) are reponed. Two sets of samples were studied for both dopanu: hvo lightly doped samples with p < 0.01 and two more heavily doped samples with p = 0.06 lo 0.12. For the lightly doped samples. ~p s u l u are analysed in terms of mntributions Gum single magnetic ions, exchange-coupled pairs and any mnlributions from the spin-orbit mupling. For Co2+ in MgO, a mntribution from spin-xbit mupling leads to a temperalure-dependent magnetic moment (p~ = 3.84 p~ at 5 K to 5.15 at 300 IC) and an apparent Curie-Weiw variation, whereas for Ni2+ in MgO. the paramagnetic x p follows Ihe Chrie-law variation. From this analysis, mncentralions of lhe dopants are delermined. Further, the lemperature independence of ,yF,/,y$ for two doping levels A and B a1 low concentrations is used lo show thal any mnlnbutions from exchange-coupled pairs are negligible. The more heavily doped samples show non-linear variations of x;' against T, presumably due lo mntributions from magnetic clusters of different sizes.
Ferromagnetism in nitrogen-doped MgO: Density-functional calculations
Physical Review B, 2009
The magnetic state of Nitrogen-doped MgO, with N substituting O at concentrations between 1% and the concentrated limit, is calculated with density-functional methods. The N atoms are found to be magnetic with a moment of 1 µB per Nitrogen atom and to interact ferromagnetically via the double exchange mechanism. The long-range magnetic order is established above a finite concentration of about 1.5% when the percolation threshold is reached. The Curie temperature TC increases linearly with the concentration, and is found to be about 30 K for 10% concentration. Besides the substitution of single Nitrogen atoms, also interstitial Nitrogen atoms, clusters of Nitrogen atoms and their structural relaxation on the magnetism are discussed. Possible scenarios of engineering a higher Curie temperature are analyzed, with the conclusion that an increase of TC is dicult to achieve, requiring a particular attention to the choice of chemistry.
Journal of Alloys and Compounds, 2014
We present magnetic properties of NiMn 2 O 4Àd (nickel manganite) which was synthesized by complex polymerization synthesis method followed by successive heat treatment and final calcinations in air at 1200°C. The sample was characterized by using X-ray powder diffractometer (XRPD), scanning electron microscopy (SEM), field-emission scanning electron microscopy (FE-SEM) and superconducting quantum interference device (SQUID) magnetometer. The XRPD and FE-SEM studies revealed NiMn 2 O 4Àd phase and good crystallinity of particles. No other impurities have been observed by XRPD. The magnetic properties of the sample have been studied by measuring the temperature and field dependence of magnetization. Magnetic measurements of M(T) reveal rather complex magnetic properties and multiple magnetic phase transitions. We show three magnetic phase transitions with transition temperatures at T M1 = 35 K (longrange antiferromagnetic transition), T M2 = 101 K (antiferromagnetic-type transition) and T M3 = 120 K (ferromagnetic-like transition). We found that the T M1 transition is strongly dependent on the strength of the applied magnetic field (T M1 decreases with increasing applied field) whereas the T M3 is field independent. Otherwise, the T M2 maximum almost disappears in higher applied magnetic fields (H = 1 kOe and 10 kOe). Magnetic measurements of M(H) show hysteretic behavior below T M3 . Moreover, hysteresis properties measured after cooling of the sample in magnetic field of 10 kOe show exchange bias effect with an exchange bias field |H EB |=196 Oe. In summary, the properties that distinguish the investigated NiMn 2 O 4-d sample from other bulk, thin film, ceramic and nanoparticle NiMn 2 O 4-d systems are the triple magnetic transitions with sharp increase of the ZFC and FC magnetizations at 120 K and the exchange bias effect. The analysis of the results and comparison with literature data allowed us to conjecture that the mixed oxidation states of Mn ions, ferromagnetic and antiferromagnetic sublattice orders and surface effects in the sample tailor these interesting magnetic properties.
Ferromagnetism in Nitrogen Doped Magnesium Oxide: a First Principle Study
2011
The formation of magnetic moment in the p-orbital doped semiconductors is named d 0 magnetism, where the ion without partially filled d states is found to be responsible for the magnetism. To study origin of magnetism in such p-orbital doped semiconductors, we report a theoretical investigation of electronic and magnetic properties of N doped MgO, with and without an oxygen vacancy. The first principle calculations have been performed using ab initio total energy calculations with in generalized gradient approximation (GGA) as embodied in projector augmented wave (PAW) method. Our results suggest that without other defects, the oxygen vacancy does not reflect magnetism. It is observed that when N, substitutes for oxygen, it shows spontaneous magnetization and affect the magnetic moment of dopant. Although, the total magnetic moment of the system is independent of the presence of oxygen vacancies and found to be 1 B.
Relaxation behaviour of Co and Ni implanted into MgO
Journal of Magnetism and Magnetic Materials, 2007
Doping magnesium oxide with cobalt and nickel by ion implantation, results in the formation of nanosized metallic clusters [Pinto, et al., Eur. Phys. J. B 45 (2005) 331]. Single crystals of [1 0 0] MgO were implanted with the transition ions, Co and Ni, with 250 keV energy and fluence of 1 Â 10 17 cm À2. After vacuum annealing at 1270 K the implanted samples exhibit superparamagnetic behaviour associated with the formation of metallic clusters. The magnetic relaxation of these clusters was studied using magnetization measurements, in order to characterize the nanosized aggregates.
Oxygen K-edge XANES investigation of NicMg1-cO solid solutions
SPECTROCHIMICA ACTA PART A-MOLECULAR AND BIOMOLECULAR SPECTROSCOPY, 2008
A series of Ni c Mg 1 − c O solid solutions are characterized by means of synchrotron radiation X-ray diffraction and X-ray absorption near-edgestructure spectroscopy at oxygen K-edge (532 eV). A dramatic drop of the pre-edge peak intensity is observed in the Ni c Mg 1 − c O system upon dilution. It can be attributed to a decrease of 3d 8 (Ni 2+)-2p(O 2−) mixing upon dilution with magnesium ions due to a decrease of the number of 3d vacancies as nickel ion is replaced by magnesium ion. Similarly, the decrease of the number of 4s and 4p vacancies also leads to a decrease of 4s4p(Ni 2+)-2p(O 2−) hybridization, and hence a drop of intensities of features B and C. The features E and F are more sensitive to the increase of the degree of disorder upon dilution than feature D, revealing that the latter is mainly dependent by the medium-range order.
Possible ferromagnetism in MgO
Solid State Communications, 2009
We study the impact of vacancies on the magnetism of MgO and TiO 2 nanoparticles, and develop fist-principle calculations to ascertain the origin of the induced polarization. Theoretically, we expect ferromagnetism only for the case of MgO with cation defects. Experimentally, we observed a small magnetic signal probably due to imperfections in the lattice order, perhaps at the nanoparticles surface.
The structural and magnetic properties of Ni2Mn1−xMxGa (M=Co, Cu)
Journal of Applied Physics, 2005
In Ni2MnGa (cubic structure of L21 type) a first order martensitic structural transition, from the parent cubic (austenitic) phase to a low temperature complex tetragonal structure, takes place at TM=202K, and ferromagnetic order in the austenitic phase sets at TC=376K. In this work, the Mn sites in Ni2MnGa have been partially substituted with magnetic Co and nonmagnetic Cu, and the influence of these substitutions on the structural and magnetic properties of Ni2Mn1−xMxGa (M=Co and Cu) have been studied by XRD and magnetization measurements. X-ray diffraction patterns indicate that the Co doped system possess a highly ordered Heusler alloy L21 type structure for 0.05<x<0.12, and the Cu doped compounds possess L21 structure for 0.05<x<0.10. The ferromagnetic ordering temperature increases with increasing Co concentration for this system, and rapidly decreases with increasing Cu concentration. Both systems show the increase in TM with increasing Co and Cu concentration. (T...