Influence of structure and cation distribution on magnetic anisotropy and damping in Zn/Al doped nickel ferrites
Julia Lumetzberger, Martin Buchner, Santa Pile, Verena Ney, Wolfgang Gaderbauer, Niéli Daffé, Marcos V. Moro, Daniel Primetzhofer, Kilian Lenz, Andreas Ney
An in-depth analysis of Zn/Al doped nickel ferrites grown by reactive magnetron sputtering is relevant due to their promising characteristics for applications in spintronics. The material is insulating and ferromagnetic at room temperature with an additional low magnetic damping. By studying the complex interplay between strain and cation distribution their impact on the magnetic properties, i.e. anisotropy, damping and g-factor is unravelled. In particular, a strong influence of the lattice site occupation of Ni$^{2+}_{\text{Td}}$ and cation coordination of Fe$^{2+}_{\text{Oh}}$ on the intrinsic damping is found. Furthermore, the critical role of the incorporation of Zn$^{2+}$ and Al$^{3+}$ is evidenced by comparison with a sample of altered composition. Especially, the dopant Zn$^{2+}$ is evidenced as a tuning factor for Ni$^{2+}_{\text{Td}}$ and therefore unquenched orbital moments directly controlling the g-factor. A strain-independent reduction of the magnetic anisotropy and damping by adapting the cation distribution is demonstrated.
We used a thermodynamics-informed first principles scheme, to calculate the temperature-dependent surface energies of nickel oxide (NiO) and nickel ferrite (NiFe2O4), two compounds that are known to deposit on the fuel rods in nuclear pressurized water reactors (PWR). These calculations predict a negative surface free energy for nickel ferrite when formed from ions in solution under PWR conditions of temperature, pressure and species concentration. Under these conditions the thermodynamics of bulk nickel ferrite yields a positive change in free energy for formation of the solid from dissolved …
The effect of epitaxial strain on the cation distribution in spinel ferrites CoFe2O4 and NiFe2O4 is investigated by GGA+U total energy calculations. We obtain a very strong (moderate) tendency for cation inversion in NiFe2O4 (CoFe2O4), in agreement with experimental bulk studies. This preference for the inverse spinel structure is reduced by tensile epitaxial strain, which can lead to strong sensitivity of the cation distribution on specific growth conditions in thin films. Furthermore, we obtain significant energy differences between different cation arrangements with the same degree of inver…
Ferrite nanocrystals are interesting material due to their rich physical properties. Here we add nonmagnetic dopants Zn and Cu to nickel ferrite nanocrystals, Ni1-xMxFe2O4 (0<=x<=1, M{\in}{Cu, Zn}), and characterize how relevant properties of the samples are modified accordingly. Basically, these dopings cause a rearrangement of Fe+3 ions into the two preexisting octahedral and tetrahedral sites. In fact, this, we show, induces pertinent magnetic properties of the doped samples. In the case of the Cu-doping, the Jahn-Teller effect also emerges, which we identify through the FTIR Spectroscopy o…
The accumulation of boron within the porous nickel ferrite (NiFe2O4, NFO) deposited on fuel rods is a major technological problem with important safety and economical implications. In this work the electronic structure of nickel ferrite is investigated using first-principles methods, and the results are combined with experimental data to analyze B incorporation into the NFO structure. Under thermodynamic equilibrium the calculations predict that the incorporation of B into the NFO structure is unfavorable. The main limiting factors are the narrow stability domain of NFO and the precipitation o…
We present calculations of magnetostriction constants for the spinel ferrites CoFe2O4 and NiFe2O4 using density functional theory within the GGA+U approach. Special emphasis is devoted to the influence of different possible cation distributions on the B site sublattice of the inverse spinel structure on the calculated elastic and magnetoelastic constants. We show that the resulting symmetry-lowering has only a negligible effect on the elastic constants of both systems as well as on the magnetoelastic response of NiFe2O4, whereas the magnetoelastic response of CoFe2O4 depends more strongly on t…
In this work, we have performed Monte Carlo simulations in a classical model for RFe$_{1-x}$Cr$_x$O$_3$ with R=Y and Lu, comparing the numerical simulations with experiments and mean field calculations. In the analyzed compounds, the antisymmetric exchange or Dzyaloshinskii-Moriya (DM) interaction induced a weak ferromagnetism due to a canting of the antiferromagnetically ordered spins. This model is able to reproduce the magnetization reversal (MR) observed experimentally in a field cooling process for intermediate $x$ values and the dependence with $x$ of the critical temperatures. We also a…
Magnetoelectric Coupling in Nickel-Cobalt Ferrite and Lanthanum Ferrite Heterostructure Composites: Experimental Evidence and Simulation-Driven Insights
The synthesis of layered ferrite-lead titanate zirconate (PZT) and lanthanum nanganite-PZT and the observation of giant magneto-electric interactions are discussed. The ferrites used in our studies included pure and Zn substituted cobalt-, nickel- and lithium ferrites. Ferromagnetic manganites used included both calcium and strontium substituted systems. The samples were prepared from 10-40 mm thick films obtained by tape-casting. Our studies showed strong ME coupling in manganite-PZT and cobalt zinc ferrite-PZT, and a giant ME effect in nickel zinc ferrite-PZT. We found evidence for Zn assist…
We prepared three ferrite nanocatalysts: (i) copper ferrite (CuFe2O4), (ii) ferrite where cobalt was substituted by nickel (NixCo1-xFe2O4, with x= 0, 0.2, 0.4, 0.6), and (iii) ferrite where nickel was substituted by zinc (ZnyNi1-yFe2O4 with y= 1, 0.7, 0.5, 0.3), by the sol-gel method. The X-ray diffraction patterns show that the ferrite samples have been crystallized in the cubic spinel structural phase. We obtained the grain size by FE-SEM images in the range of 10-70 nm, and their magnetic properties by VSM. Next, carbon nanotubes were grown on these nanocatalysts by the CCVD method. We show…
The observation of strong magnetoelectric effects is reported in thick film bilayers and multilayers of ferrite-lead titanate zirconate (PZT) and lanthanum nanganite-PZT. The ferrites used in our studies included pure and zinc substituted cobalt-, nickel- and lithium ferrites. Samples were prepared by sintering 10-40 mm thick films obtained by tape-casting. Measurements of ME voltage coefficients at 10-1000 Hz indicated a giant ME effect in nickel ferrite-PZT, but a relatively weak coupling in other ferrite-PZT and manganite-PZT systems. Multilayers prepared by hot pressing was found to show a…
A serious concern in the safety and economy of a pressurized water nuclear reactor is related to the accumulation of boron inside the metal oxide (mostly NiFe${}_{2}$O${}_{4}$ spinel) deposits on the upper regions of the fuel rods. Boron, being a potent neutron absorber, can alter the neutron flux causing anomalous shifts and fluctuations in the power output of the reactor core. This phenomenon reduces the operational flexibility of the plant and may force the down-rating of the reactor. In this work an innovative approach is used to combine first-principles calculations with thermodynamic dat…
Spinel ferrites in general show a rich interplay of structural, electronic, and magnetic properties. Here, we particularly focus on zinc ferrite (ZFO), which has been observed experimentally to crystallise in the cubic $normal$ spinel structure. However, its magnetic ground state is still under dispute. In addition, some unusual magnetic properties in ZFO thin films or nanostructures have been explained by a possible partial cation inversion and a different magnetic interaction between the two cation sublattices of the spinel structure compared to the crystalline bulk material. Here, density f…
We utilize spin Hall magnetoresistance (SMR) measurements to experimentally investigate the pure spin current transport and magnetic properties of nickel ferrite (NiFe2O4,NFO)/normal metal (NM) thin film heterostructures. We use (001)-oriented NFO thin films grown on lattice-matched magnesium gallate substrates by pulsed laser deposition, which significantly improves the magnetic and structural properties of the ferrimagnetic insulator. The NM in our experiments is either Pt or Ta. A comparison of the obtained SMR magnitude for charge currents applied in the [100]- and [110]-direction of NFO y…
The comparative study of the substitution of zinc and lithium for iron in the "114" ferrites, YBaFe4O7 and CaBaFe4O7, shows that these diamagnetic cations play a major role in tuning the competition between ferrimagnetism and magnetic frustration in these oxides. The substitution of Li or Zn for Fe in the cubic phase YBaFe4O7 leads to a structural transition to a hexagonal phase YBaFe4-xMxO7, for M = Li (0.30 < x < 0.75) and for M = Zn (0.40 < x < 1.50). It is seen that for low doping values i.e. x = 0.30 (for Li) and x = 0.40 (for Zn), these diamagnetic cations induce a strong ferrimagnetic c…
Spinel ferrite Cu1-xZnxFe2O4 nanofibers over a compositional range 0 < x < 1 were prepared by electrospinning combined with sol-gel method. The influence of Zn2+ ions substitution on morphology, structure, and magnetic properties of copper ferrite has been investigated. The results show that surface of CuFe2O4 nanofibers consists of small open porosity, while surface of doped nanofibers reveals smooth and densified nature. With increasing Zn substitution, saturation magnetization initially increases and then decreases with a maximum value of 58.4 emu/g at x = 0.4, coercivity and square ratio a…
The recent discovery of superconductivity in infinite-layer nickelate films has aroused great interest since it provides a new platform to explore the mechanism of high-temperature superconductivity. However, superconductivity only appears in the thin film form and synthesizing superconducting nickelate films is extremely challenging, limiting the in-depth studies on this compound. Here, we explore the critical parameters in the growth of high quality nickelate films using molecular beam epitaxy (MBE). We found that stoichiometry is crucial in optimizing the crystalline structure and realizing…
The magnetization of thin films of cobalt ferrite frequently falls far below the bulk value of 455 kAm-1, which corresponds to an inverse cation distribution in the spinel structure with a significant orbital moment of about 0.6 muB that is associated with the octahedrally-coordinated Co2+ ions. The orbital moment is responsible for the magnetostriction and magnetocrystalline anisotropy, and its sensitivity to imposed strain. We have systematically investigated the structure and magnetism of films produced by pulsed-laser deposition on different substrates (TiO2, MgO, MgAl2O4, SrTiO3, LSAT, La…
Many technologically useful magnetic oxides are ferrimagnetic insulators, which consist of chemically distinct cations. Here, we examine the spin dynamics of different magnetic cations in ferrimagnetic NiZnAl-ferrite (Ni$_{0.65}$Zn$_{0.35}$Al$_{0.8}$Fe$_{1.2}$O$_4$) under continuous microwave excitation. Specifically, we employ time-resolved x-ray ferromagnetic resonance to separately probe Fe$^{2+/3+}$ and Ni$^{2+}$ cations on different sublattice sites. Our results show that the precessing cation moments retain a rigid, collinear configuration to within $\approx$2$^\circ$. Moreover, the effe…
Single phase nickel-cobalt-titanate thin films with a formula A1+2xTi1-xO3, where A is Ni2+,Co2+ and -0.25<x<1, were grown by pulsed laser deposition on sapphire substrates. There is a large window in which both Ni/Co ratio and x can be chosen independently. In the prototype ilmenite and corundum structures one third of the octahedra are vacant. The reported structure is obtained by filling vacant (x>0) or emptying filled (x<0) octahedra. When x = 1 all octahedra are filled. Two factors controlling the magnetism and crystal distortion are identified. First is a direct overlap between the adjac…
The inverse spinels CoFe2O4 and NiFe2O4, which have been of particular interest over the past few years as building blocks of artificial multiferroic heterostructures and as possible spin-filter materials, are investigated by means of density functional theory calculations. We address the effect of epitaxial strain on the magneto-crystalline anisotropy and show that, in agreement with experimental observations, tensile strain favors perpendicular anisotropy, whereas compressive strain favors in-plane orientation of the magnetization. Our calculated magnetostriction constants $λ_{100}$ of about…
Magnetic insulators have been intensively studied for over 100 years, and they, in particular ferrites, are considered to be the cradle of magnetic exchange interactions in solids. Their wide range of applications include microwave devices and permanent magnets . They are also suitable for spintronic devices owing to their high resistivity, low magnetic damping, and spin-dependent tunneling probabilities. The Curie temperature is the crucial factor determining the temperature range in which any ferri/ferromagnetic system remains stable. However, the record Curie temperature has stood for over …
The mixed ferrite-cobaltites LnFe0.5Co0.5O3, with Ln = Eu & Dy have been prepared by a sol-gel method and the samples have been characterized using X-ray diffraction and electron microscopy. The magnetic investigations reveal that both samples ordered in canted antiferromagnetic structures near room temperature. The Dzyaloshinskii-Moriya or antisymmetric exchange interaction induces weak ferromagnetism due to canting of the antiferromagnetically ordered spins. In the case of Ln-Fe-Co orthoferrites, two magnetic sublattices (Ln3+-4f and Fe3+/Co3+-3d) generally align in opposite directions and i…
CoFe2O4 nanoparticles were synthesized using gelatin as a polymerizing agent. Structural, morphological and magnetic properties of samples treated at different temperatures were investigated by X-ray diffraction, scanning electron microscopy, Mossbauer spectroscopy and magnetization measurements. Our results revealed that the samples annealed at 623 K and temperatures above 973 K have a cation distributions given by (Co0.19Fe0.81)[Co0.81Fe1.19]O4 and (Co0.06Fe0.94)[Co0.94Fe1.06]O4, respectively. The particle sizes varied from 73 to 296 nm and the magnetocrystalline anisotropy, K1, has values r…
The structural and magnetic properties of Zn/Al doped nickel ferrite thin films can be adjusted by changing the Zn and Al content. The films are epitaxially grown by reactive magnetron sputtering using a triple cluster system to sputter simultaneously from three different targets. Upon the variation of the Zn content the films remain fully strained with similar structural properties, while the magnetic properties are strongly affected. The saturation magnetization and coercivity as well as resonance position and linewidth from ferromagnetic resonance (FMR) measurements are altered depending on…
Varying the substrate temperature changes structural and magnetic properties of spinel ferrite NZFO thin films. XRD of films grown at different temperature display only 004 reflections, without any secondary peaks, showing growth orientation along the c axis. We find an increase in crystalline quality of these thin films with the rise of substrate temperature. The surface topography of the thin films grown on various growth temperatures conditions reveal that these films are smooth with low roughness, however the thin films grown at 800 C exhibit lowest average and rms roughness among all thin…
Manganese ferrite (MnFe2O4) and copper doped manganese ferrite (Mn0.75Cu0.25Fe2O4) soft materials were synthesized through solid-state sintering method. The phase purity and quality were confirmed from x-ray diffraction patterns. Then the samples were subjected to neutron diffraction experiment and the diffraction data were analyzed using FullProf software package. The surface morphology of the soft material samples was studied using a scanning electron microscope (SEM). Crystal parameters, crystallite parameters, occupancy at A and B sites of the spinel structure, magnetic moments of the atom…
The non-equilibrium cation site occupancy in nanosized zinc ferrites (6-13 nm) with different degree of inversion (0.2 to 0.4) was investigated using Fe and Zn K-edge x-ray absorption spectroscopy XANES and EXAFS, and magnetic measurements. The very good agreement between experimental and ab-initio calculations on the Zn K-edge XANES region clearly show the large Zn2+(A)--Zn2+[B] transference that takes place in addition to the well-identified Fe3+[B]--Fe3+(A) one, without altering the long-range structural order. XANES spectra features as a function of the spinel inversion were shown to depen…
Ferrites with (inverse) spinel structure display a large variety of electronic and magnetic properties making some of them interesting for potential applications in spintronics. We investigate the thermally induced interdiffusion of Ni$^{2+}$ ions out of NiO into Fe$_3$O$_4$ ultrathin films resulting in off-stoichiometric nickelferrite-like thin layers. We synthesized epitaxial Fe$_3$O$_4$/NiO bilayers on Nb-doped SrTiO$_3$(001) substrates by means of reactive molecular beam epitaxy. Subsequently, we performed an annealing cycle comprising three steps at temperatures of 400\,$^{\circ}$C, 600\,…
We report the synthesis of Y-substituted Mg-Zn ferrites using conventional standard ceramic technique. XRD patterns confirm the single phase cubic spinel structure up to x = 0.03 and appearance of a secondary phase of YFeO3for higher Y contents. FESEM images depict the distribution of grains and EDS spectra confirmed the absence of any unwanted element. Completion of solid state reaction and formation of spinel structure has been revealed from FTIR spectra. The FTIR data along with lattice constant, bulk density and porosity were further used to calculate the stiffness constant (Cij), elastic …
The effects of Ni$^{2+}$ substitution on the structure (lattice parameters, cations distribution, average cations radii, cation-cation/anion bond lengths and angles) and the soft magnetic properties of Mg$_{1-x}$Ni$_x$Fe$_2$O$_4$ ($0 \le x \le 1.0$) nanocrystals have been studied by x-ray diffraction with Rietveld refinement, transmittance electron microscopy, Mossbauer spectroscopy and magnetization measurements. The mostly inverse spinel structure was found in MgFe$_2$O$_4$ nanoparticles and the inversion factor is further increased by Ni-substitution up to a complete inversion in NiFe$_2$O$…
Layered ferromagnetic-piezoelectric composites show mechanical strain mediated electromagnetic coupling. Here we discuss dielectric and piezoelectric properties of ferrite-lead zirconate titanate (PZT) and lanthanum manganite-PZT samples. Results of our investigations on dielectric and pyroelectric properties of multilayer ferromagnetic-piezoelectric are presented here. Lead zircinate-titanate PbZrxTi1-xO3 (PZT) was used for the piezoelectric phase in all the structures. The following materials were used for the ferromagnetic component: nickel-zinc ferrites Ni0.9Zn 0.1Fe2O4 (NFO1) and Ni0.8Zn0…
Inter-valence charge transfer (IVCT) is electron transfer between two metal $M$ sites differing in oxidation states through a bridging ligand: $M^{n+1} + M'^{m} \rightarrow M^{n} + M'^{m+1}$. It is considered that IVCT is related to the hopping probability of electron (or the electron mobility) in solids. Since controlling the conductivity of ferromagnetic semiconductors (FMSs) is a key subject for the development of spintronic device applications, the manipulation of the conductivity through IVCT may become a new approach of band engineering in FMSs. In Ru-doped cobalt ferrite CoFe$_2$O$_4$ (…
Spin and orbital magnetic moments of cationic iron, cobalt, and nickel clusters have been determined from x-ray magnetic circular dichroism spectroscopy. In the size regime of $n = 10 - 15$ atoms, these clusters show strong ferromagnetism with maximized spin magnetic moments of 1~$μ_B$ per empty $3d$ state because of completely filled $3d$ majority spin bands. The only exception is $\mathrm{Fe}_{13}^+$ where an unusually low average spin magnetic moment of $0.73 \pm 0.12$~$μ_B$ per unoccupied $3d$ state is detected; an effect, which is neither observed for $\mathrm{Co}_{13}^+$ nor $\mathrm{Ni}…
Magnetic properties of silver(II) compounds have been of interest in recent years. In covalent compounds, the main mechanism of interaction between paramagnetic sites is the superexchange via the connecting ligand. To date, little is known of magnetic interactions between Ag(II) cations and other paramagnetic centres. It is because only a few compounds bearing Ag(II) cation and other paramagnetic transition metal cation are known experimentally. Recently the high-pressure synthesis of ternary silver(II) fluorides with 3d metal cations AgMF4 (M = Co, Ni, Cu) was predicted to be feasible. Here, …
Spin-polarized density functional calculations, magnetization, and neutron diffraction measurements are carried out to investigate the magnetic exchange interactions and strong correlation effects in Yb substituted inverse spinel nickel ferrite. In the pristine form, the compound is found to be a mixed insulator under the Zaanen-Sawtazsky-Allen classification scheme as it features both charge transfer and Mott insulator mechanism. Estimation of magnetic exchange couplings reveals that both octahedral-octahedral and octahedral-tetrahedral spin-spin interactions are antiferromagnetic which is ty…
New equiatomic nickel germanides MgNiGe, SrNiGe, and BaNiGe have been synthesized from the elements in sealed tantalum tubes using a high-frequency furnace. The compounds were investigated by X-ray diffraction both on powders and single crystals. MgNiGe crystallizes with TiNiSi structure type, space group Pnma, Z = 4, a = 6.4742(2) A, b = 4.0716(1) A, c = 6.9426(2) A, wR2 = 0.033, 305 F2 values, 20 variable parameters. SrNiGe and BaNiGe are isotypic and crystallize with anti-SnFCl structure type (Z = 4, Pnma) with a = 5.727(1) A, b = 4.174(1) A, c = 11.400(3) A, wR2 = 0.078, 354 F2 values, 20 …
Recently theoretical works predict that some semiconductors (e.g. ZnO) doped with magnetic ions are diluted magnetic semiconductors (DMS). In DMS magnetic ions substitute cation sites of the host semiconductor and are coupled by free carriers resulting in ferromagnetism. One of the main obstacles in creating DMS materials is the formation of secondary phases because of the solid-solubility limit of magnetic ions in semiconductor host. In our study transition metal ions were implanted into ZnO single crystals with the peak concentrations of 0.5-10 at.%. We established a correlation between stru…
Nanoparticles (NPs) which combine several magnetic phases offer wide perspectives for cutting edge applications because of the high modularity of their magnetic properties. Besides the addition of the magnetic characteristics intrinsic to each phase, the interface that results from core-shell and, further, from onion structures leads to synergistic properties such as magnetic exchange coupling. Such a phenomenon is of high interest to overcome the superparamagnetic limit of iron oxide NPs which hampers potential applications. In this manuscript, we report on the design of NPs with an onion-lik…
