Ferromagnetic Ni2 Research Articles

Magnetoelectric coupling and thermoelectric behaviors in Ni-doped CuCrO[formula omitted] crystallites

A novel and effective approach to improve thermoelectric conversion efficiency is of utmost importance for its commercial viability. The increased ferromagnetism caused by the Ni-doping alters the antiferromagnetic interactions between Cr3+ ions in CuCrO2 and likely produces the conical-like spin component. The magnetostrictive ferromagnetic Ni2+ doped CuCrO2 generates stress through the elastic property at the grain interface and piezoelectricity which couples and generates an electric field. The built-in electric field and magnetic scattering produced by magnetic doping reduce carrier concentration and mobility and raise the Seebeck coefficient. The engendered multiferroic nature and the alteration of electron transport properties with magnetic phase transition from ferromagnetic to paramagnetic of Ni2+ doped CuCrO2 are evidenced by magnetoresistance and vibrating-sample magnetometry (VSM) investigations. The magnetic inclusion of Ni2+ generates carrier magnon drag which steers the highest Seebeck coefficient of 625 μV/K at 100 °C. The conductivity of 4203 S/m and the Seebeck coefficient of 386 μV/K leads excellent power factor (S2σ) of 0.62 mW/mK2 and ZT of 0.163 at 700 °C. The Ni2+ dopants, on the other hand, cause broad frequency phonon scattering, which significantly lowers the lattice thermal conductivity of CuCrO2. This study demonstrates how magnetic particle-induced thermoelectromagnetic coupling effects can significantly boost the efficiency of electro-thermal conversion.

Synthesis, Structural and Magnetic Characterization of Superparamagnetic Ni0.3Zn0.7Cr2−xFexO4 Oxides Obtained by Sol-Gel Method

The sol-gel process was used to produce ferrite Ni0.3Zn0.7Cr2−xFexO4 compounds with x = 0, 0.4, and 1.6, which were then subsequently calcined at several temperatures up to 1448 K for 48 h in an air atmosphere. X-ray diffraction (XRD), scanning electron microscopy (SEM), vibrating sample magnetometer (VSM), and 57Fe Mössbauer spectrometry were used to examine the structure and magnetic characteristics of the produced nanoparticles. A single-phase pure Ni0.3Zn0.7Cr2−xFexO4 nanoparticle had formed. The cubic Fd3¯m spinel structure contained indexes for all diffraction peaks. The crystallite size is a perfect fit for a value of 165 ± 8 nm. Based on the Rietveld analysis and the VSM measurements, the low magnetization Ms of Ni0.3Zn0.7Cr2−xFexO4 samples was explained by the absence of ferromagnetic Ni2+ ions and the occupancy of Zn2+ ions with no magnetic moments in all tetrahedral locations. Moreover, because of the weak interactions between Fe3+ ions in the octahedral locations, the magnetization of the current nanocrystals is low or nonexistent. According to Mössbauer analyses, the complicated hyperfine structures are consistent with a number of different chemical atomic neighbors, such as Ni2+, Zn2+, Cr3+, and Fe3+ species that have various magnetic moments. A Fe-rich neighbor is known to have the highest values of the hyperfine field at Fe sites, while Ni- and Cr-rich neighbors are responsible for the intermediate values and Zn-rich neighbors are responsible for the quadrupolar component.

Effect of Cu Incorporation on Structure, Densification and Magnetic Properties of Polycrystalline Li<sub><i>x</i></sub>Ni<sub>0.2</sub>Zn<sub>0.8-2<i>x</i></sub>Fe<sub>2+<i>x</i></sub>O<sub>4</sub> Ceramics

The polycrystalline LixNi0.2Zn0.8-2xFex+2O4 and LixNi0.1Cu0.1Zn0.8-2xFex+2O4 (x = 0.0, 0.1, 0.2, and 0.3) ferrites were synthesized by the standard solid-state reaction method. The compound was sintered at 1150˚C for 5 hours. The effect of Cu substitution and its impact on the crystal structure, microstructure, complex initial permeability and magnetization of the Ni-Zn ferrites were studied. The effect of Li+ incorporation on the properties mentioned above was also investigated. X-ray diffraction patterns of the samples indicated a single cubic spinel structure for both the compound. No effect of Cu addition on crystal structure was observed. The density of the ferrites was found to be enhanced because of adding Li whereas the porosity of the samples decreased with the content of Li ions. The average value of grain size increased with the addition of Li content. The samples having Cu ions formed bigger size grains. Frequency-dependent complex initial permeability, loss tangent, and relative quality factor were studied at room temperature using an Impedance analyzer in the range of 100 Hz - 120 MHz regions. In the low-frequency region, the prepared samples exhibited a high value of permeability and after a certain frequency, the permeability falls. The value of permeability enhanced with the increase in Li whereas loss tangent was found to be reduced. The relative quality factor graphs described that the compound has excellent frequency stability up to a certain frequency which is suitable to be used in inductors, resistors, capacitors, etc. Initial permeability for LixNi0.1Cu0.1Zn0.8-2xFex+2O4 ferrites was found high than LixNi0.2Zn0.8-2xFex+2O4 which might be attributed to having bigger size grains of Cu containing samples because of easy movement of domain wall in bigger size grains. The values of saturation magnetization (Ms) were calculated for both compounds from M-H hysteresis loops and it enhanced with the increase in Li content which might be related to the modification of predominant exchange interactions between the cations. The Cu-containing compound exhibited higher values of saturation magnetization. The cation distribution reflects this increment because ferromagnetic Ni2+ and paramagnetic Cu2+ ions occupied in the B-sites and the diamagnetic Zn and paramagnetic Li occupied in the A-sites; therefore, net magnetic moments increased gradually. The studied materials might be used as an alternative to Pb-based compounds and would be environment friendly.

B-site ordering effect on structural and magnetic properties of ‘Y’-modified double perovskite La2NiMnO6 nanoparticles

Rietveld refinement profile of X-ray diffraction pattern confirms the pure-phase rhombohedral structure of La2NiMnO6 (LNMO) and ‘Y’-doped LNMO nanoparticles corresponding to the space group R$$\stackrel{-}{3}$$c (SG No.: 167) with the crystallite size lying in the range of 25–16 nm. The antiferromagnetic (AFM) to strong ferromagnetic (FM) transition has been observed through M–H hysteresis loops from room temperature to extremely low temperature (2 K) for LNMO and ‘Y’-doped LNMO nanoparticles. An extraordinary magnetic moment of 4.16 to 6.25 µB per formula unit was achieved after the doping of ‘Y’ (nominally 2 to 4%) into LNMO. The temperature-dependent magnetization studies confirm the transition temperature (~ 273 K) for LNMO and LNMO2 (LNMO-2%Y) nanoparticles due to the antisite defects beside the FM ordering of the Ni-Mn sites and lower transition temperature (~ 230 K) for LNMO4 due to the local structural distortion and the superexchange interaction in FM Ni2+($${t}_{2g}^{6}{e}_{g}^{2}$$) – O($$2p$$) – Mn4+($${t}_{2g}^{3}{e}_{g}^{0}$$).

Significant high-frequency electromagnetic wave absorption performance of Ni2+xMn1−xGa alloys

The electromagnetic wave (EMW) absorption properties in Heusler-type ferromagnetic Ni2+xMn1−xGa alloys were systematically investigated. Significant electromagnetic absorption performance at 2.0–18.0 GHz was observed for Ni2+xMn1−xGa alloys. The values of the complex permittivity (er) and permeability (μr), as well as the reflection loss (RL), peak frequency (fm) and bandwidth (Δf) of Ni2+xMn1−xGa can be effectively tuned by the alloy component (Ni/Mn ratio). The magnetic loss factor (tan δμ) shows pronounced multi-resonance behavior, and dielectric loss factor (tan δe) has dramatic dielectric relaxation. The RL exceeding − 10 dB corresponding to 90% absorption of incident microwave can be achieved for the Ni2MnGa in a broad frequency range of 6.3–18.0 GHz together with the thickness from 1.66 to 4.75 mm. Particularly, the maximum RL reaches − 49.1 dB at 13.3 GHz with the thickness of 2.57 mm for Ni2MnGa. The present results indicated that the ferromagnetic Ni2+xMn1−xGa alloys could be attractive candidates for broadband and high-frequency EMW absorption.

Synthesis, structure and properties of Ni(II) coordination polymer based on α,α-dimethyl substituted zoledronate

The reaction of α,α-dimethyl substituted derivative of zoledronic acid with Ni(II) afforded 1D coordination polymer, Ni3(HL)2(H2O)6·6H2O (1). The title compound possess crystallographically and spectroscopically distinct Ni1 and Ni2 centers characterized by tetragonality distortion parameter T = 0.97 and 1.04, respectively, and is isomorphous with recently reported Co3(HL)2(H2O)6·6H2O complexes based on α,α-dimethyl and cyclopropyl substituted zoledronate derivatives.Detailed analysis of thermal stability of 1 revealed that partly dehydrated [Ni3(HL)2(H2O)3] still retains its architecture and structural integrity of coordinated ligands. Exploring supramolecular interactions that build up the crystal of 1 and related Co(II) complexes allowed a conclusion that distinct dehydration pathways observed for each compound may be correlated with subtle differences in 3D crystals packing. Ni2(P2O7) salt was identified as the major final product of thermolysis of 1.The magnetic properties of 1 analyzed in term of a spin-1 Heisenberg Ni2Ni1Ni2 trimer chains model revealed antiferromagnetic Ni1⋯Ni2 interactions within the trimers (J1 = −7.32 cm−1) and ferromagnetic Ni2⋯Ni2 intertrimers coupling (ΘW = 1.72 K). Furthermore, different values of the axial zfs D parameters and the g-factors were assigned to the Ni1 and Ni2 centers.

Magnetite Tailoring the Magnetic Properties of Mn0.5Cu0.5Fe2O4 Ferrites by Ni Substitution

Ni substituted Mn0.5Cu0.5Fe2O4 with general formula Mn0.5Cu0.5-xNixFe2O4 with x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5 were prepared using sol-gel auto-combustion technique. Single phase polycrystalline samples were confirmed to spinel structure by using X-ray diffraction. The structural parameters have been evaluated and subsequently confirmed by the software CELL. The lattice parameters did not show any consistent decreasing or increasing trend but crystallite size was decreased due to the incorporation of Ni contents at Cu-sites in the structure. It was observed that with increasing nickel concentration, saturation magnetization increased but coercivity decreased, which could be attributed to the substitution of soft ferromagnetic Ni2+ ions at diamagnetic Cu2+ sites.

Self-assembly of a [Ni8] carbonate cube incorporating four μ4-carbonato linkers through fixation of atmospheric CO2by ligated [Ni2] complexes

The communication reports the synthesis, characterization, and magnetic behavior of a novel μ4-carbonato supported and imidazole capped ligated nickel cage [Ni8(μ-H2bpmp)4(μ4-CO3)4(ImH)8](NO3)4·2H2O (1) through self-assembly of ligand bound ferromagnetic Ni2 building blocks. Structural analysis indicates newer geometrical features for the coordination cage formation and dominant interdimer antiferromagnetic coupling resulting in a diamagnetic ground state.

Magnetic properties of LiNi0.5Mn0.47Al0.03O2 as positive electrode for Li-ion batteries

The layered LiNi0.5Mn0.47Al0.03O2 was synthesized by wet chemical method and characterized by X-ray diffraction and analysis of magnetic measurements. The powders adopted the α-NaFeO2 structure. This substitution of Al for Mn promotes the formation of Li(Ni0.472+Ni0.033+Mn0.474+Al0.033+)O2 structures and induces an increase in the average oxidation state of Ni, thereby leading to the shrinkage of the lattice unit cell. The concentration of antisite defects in which Ni2+ occupies the (3a) Li lattice sites in the Wyckoff notation has been estimated from the ferromagnetic Ni2+(3a)–Mn4+(3b) pairing observed below 140 K. The substitution of 3% Al for Mn reduces the amount of antisite defects from 7% to 6.4–6.5%. The analysis of the magnetic properties in the paramagnetic phase in the framework of the Curie–Weiss law agrees well with the combination of Ni2+ (S = 1), Ni3+ (S = 1/2) and Mn4+ (S = 3/2) spin-only values. Delithiation has been made by the use of K2S2O8. According to this process, known to be softer than the electrochemical one, the nickel ions in the (3b) sites are converted into Ni4+ in the high spin configuration, while Ni2+(3a)–Mn4+(3b) ferromagnetic pairs remain, as the Li+(3b) ions linked to the Ni2+(3a) ions in the antisite defects are not removed. The results show that the antisite defect is surrounded by Mn4+ ions, implying the nonuniform distribution of the cations in agreement with previous NMR and neutron experiments.

Effect of magnetic field on the morphology and fine structure of low-temperature martensite phase in a ferromagnetic Ni2.08Mn0.96Ga0.96 alloy

The morphology and fine structure of high-temperature austenitic and low-temperature martensitic phases in a ferromagnetic Ni2.08Mn0.96Ga0.96 alloy and the effect of magnetic field on the peculiarities of the martensite formation have been studied. The Ni2.08Mn0.96Ga0.96 alloy in the initial cast and annealed states was found to undergo martensitic and magnetic phase transformations at temperatures M s = 280 K, M f = 265 K, A s = 280 K, A f = 295 K, and T C = 375 K, respectively. Above M s, the alloy is in a metastable premartensitic state, which leads to a characteristic diffuse scattering and tweed contrast when studying by electron microscopy. An applied magnetic field of up to 600 kA/m was found to affect the martensitic transformation in the alloy. The field application leads to changes in the morphology and fine structure of martensite due to orientation along the field direction of the magnetizations of the energetically advantageous (in terms of the directions of the magnetization vectors) c domains of the existing orientation variants of the martensite crystals having a packet pairwise-twinned morphology. The martensitic structure of the Ni2.08Mn0.96Ga0.96 alloy already formed previously during cooling is not affected by an external magnetic field with a strength of up to 600 kA/m.

Above-room-temperature ferromagnetic Ni2+-doped ZnO thin films prepared from colloidal diluted magnetic semiconductor quantum dots

We report the preparation of spin-coated nickel-doped zinc oxide nanocrystalline thin films using high-quality colloidal diluted magnetic semiconductor (DMS) quantum dots as solution precursors. These films show robust ferromagnetism with Curie temperatures above 350K and 300K saturation moments up to 0.1Bohr magnetons per nickel. These results demonstrate a step toward the use of colloidal zero-dimensional DMS nanocrystals as building blocks for the bottom-up construction of more complex ferromagnetic semiconductor nanostructures.

Ultrasound-induced martensitic transition in ferromagnetic Ni2.15Mn0.81Fe0.04Ga shape memory alloy

Abstract The experimental observation of direct and reverse martensitic transformation due to ultrasound processing of Ni–Mn–Ga alloy is discussed. It was found that martensite–austenite as well as austenite–martensite structural transitions can be induced by the intense ultrasound at constant temperature. During the experiments low magnetic field susceptibility measurements and optical detection of twin domains arising due to martensitic transformation were performed in situ. The non-thermal nature of the effect is confirmed making use of the pulsed ultrasound technique.

Spin-wave dispersion and sublattice magnetization in NiCl2

NiCl2 is a Heisenberg planar antiferromagnet composed of hexagonal ferromagnetic Ni2+ sheets with effective XY symmetry weakly coupled antiferromagnetically to adjacent Ni2+ sheets. The near two-dimensionality dimples a directionally-dependent spin-wave renormalization together with an unusual temperature dependence on the sublattice magnetization, gap energy and specific heat. The authors report an inelastic neutron scattering study of the spin waves both at low temperatures and, for selected q-vectors, for temperatures up to TN=52.3K. The sublattice magnetization has been measured from 1.5K to TN. A renormalized spin-wave theory, which does not contain any assumptions about the temperature dependence of the energy gap, has been developed. The authors deduce JNN=21.70K and JNNN=-4.85K (H=-2 Sigma i>jJijSi.Sj). Using these interaction constants and the renormalized spin-wave theory, the temperature-dependent dispersion relations (together with the sublattice magnetization) and the gap energy up to approximately 0.4 TN are properly predicted.