Non-magnetic Al3 Research Articles

Tailoring Dzyaloshinskii-Moriya Interaction and Spin-Hall Topological Hall Effect in Insulating Magnetic Oxides by Interface Engineering.

Chiral spin textures, as exotic phases in magnetic materials, hold immense promise for revolutionizing logic, and memory applications. Recently, chiral spin textures have been observed in centrosymmetric magnetic insulators (FMI), due to an interfacial Dzyaloshinskii-Moriya interaction (iDMI). However, the source and origin of this iDMI remain enigmatic in magnetic insulator systems. Here, the source and origin of the iDMI in Pt/Y3Fe5O12 (YIG)/substrate structures are deeply delved by examining the spin-Hall topological Hall effect (SH-THE), an indication of chiral spin textures formed due to an iDMI. Through carefully modifying the interfacial chemical composition of Pt/YIG/substrate with a nonmagnetic Al3+ doping, the obvious dependence of SH-THE on the interfacial chemical composition for both the heavy metal (HM)/FMI and FMI/substrate interfaces is observed. The results reveal that both interfaces contribute to the strength of the iDMI, and the iDMI arises due to strong spin-orbit coupling and inversion symmetry breaking at both interfaces in HM/FMI/substrate. Importantly, it is shown that nonmagnetic substitution and interface engineering can significantly tune the SH-THE and iDMI in ferrimagnetic iron garnets. The approach offers a viable route to tailor the iDMI and associated chiral spin textures in low-damping insulating magnetic oxides, thus advancing the field of spintronics.

Effect of Al substitution on the magnetic, optical and electronic properties of KBiFe2O5 brownmillerite

We reveal the influence of non-magnetic Al3+ ion on magnetic, optical and electronic properties of KBiFe2O5. Al doped KBiFe2-xAlxO5 (x = 0, 0.2, 0.4) are synthesized by citrate combustion method. All the samples are found to be crystalized in monoclinic structure with P2/c space group. With Al doping, the grain size of the samples is reduced however, Fe ions maintain its +3 state. A mere difference in the low temperature zero field cooling and field cooling curve discards the multiple magnetic phases at low temperature, however, with Al, an improved magnetic moment is detected in the magnetic isotherms. A schematic model is adopted to explain the enhanced magnetization. Furthermore, the magnetic anomaly around the dielectric transition (760–780 K) depicts an existence of magnetoelectric coupling in all the samples. The optical band gap is reduced from 1.73 eV to 1.69 eV with Al doping. Extensive dielectric and electric modulus analysis is carried out to explore the conduction as well as relaxation process in the parent and Al doped system. The activation energy estimated from the electric modulus is (0.412 ± 0.021) eV for x = 0 and (0.370 ± 0.025) eV for x = 0.2 respectively but surprisingly, Al doping with x = 0.4 shows a completely different relaxation mechanism. Moreover, the frequency dependent ac conductivity is also explained and agrees well with the electric modulus data.

Magnetocaloric effect in aluminum doped ErCr1−xAlxO3 orthochromites

Aluminum-doped ErCr1-xAlxO3 orthochromites prepared via autocombustion technique were investigated for their magnetic and magnetocaloric properties. X-ray diffraction confirmed that samples were orthorhombic phases with the Pbnm space group without a trace of any impurity. As analyzed via Rietveld refinement of XRD data, structural parameters such as lattice parameters, volume, bond angle, and bond lengths were affected by doping nonmagnetic Al3+ in the compound. ErCrO3 possesses the long-range antiferromagnetic ordering with a weak display ferromagnetism at TN =133 K. Low-temperature high-field magnetic study shows a decrease in Neel temperature (TN ∼ 114 K for x = 0.5), suggesting magnetic ordering suppression due to Al3+ doping. The asymptotic paramagnetic Curie temperature Tcw = −25 K suggests the predominance of antiferromagnetic interactions in ErCrO3 orthochromites, which was observed to increase with Al3+ doping. Isothermal magnetization data show changes in magnetic entropy (−ΔSMmax) and relative cooling power (RCP). The magnetic entropy change, −ΔSMmax, for ErCrO3 estimated from magnetization measurements show 11.60 J kg−1 K−1 at 11 K and a relative cooling power (RCP) of 209.4 J kg−1 at 5 T applied field. While ErCr0.75Al0.25O3 show a maximum magnetic entropy of 11.52 J kg−1 K−1 at 11 K with a 5 T applied field and RCP of 186.66 J kg−1, whereas ErCr0.5Al0.5O3 displayed −ΔSMmax of 11.63 J kg−1 K−1 at 5 K with a 5 T applied field and RCP value of 160.78 J kg−1. The results show that nonmagnetic doping, such as Al3+, could maintain the compound’s magnetocaloric property to an extent.

Influence of Fe3+ substitution by Al3+ on the structural, microstructural, and magnetic properties of Co0.2Ni0.3Zn0.5Fe2O4 nanoparticles

A series of aluminum-substituted ferrite nanoparticles, Co0.2Ni0.3Zn0.5Fe2-xAlxO4 (0 ≤ x ≤ 1) was synthesized using the polyol method. The structural analysis confirmed the formation of pure cubic ferrispinels. The unit cell parameter decreased monotonically with increasing Al3+ content obeying Vegard's law. Besides, it was found that Al3+ ions prefer to enter octahedral sites. The produced particles consisted of roughly spherical ultrasmall nanocrystals with an average particle size of ∼3-6 nm. The nanoparticles are superparamagnetic with magnetic features (blocking temperature, saturation magnetization and Curie temperature) showing a decrease with the increase in Al3+ content. The magnetic tendency correlates with the weakening of the superexchange interactions in the spinel sublattices caused by substituting the non-magnetic Al3+ ions for Fe3+ ones. While, the coercivity and effective magnetic anisotropy increased with the increase of Al3+ concentration, suggesting the development of high surface anisotropy that largely compensates for the decrease of intrinsic magnetic anisotropy caused by the magnetic dilution.

Effect of coercive aluminium on the structural and magnetic characteristics of calcium and magnesium based hexaferrites

Aluminum substituted Calcium-Magnesium (Ca-Mg) hexaferrites having general formula Ca0.5Mg0.5Fe12-xAlxO19 (where x is increased with increment of 0.5 from 0.0 to 2.0) are prepared by sol–gel auto combustion technique. X-ray diffraction patterns confirm the hexagonal structure with no evidence of secondary phases. The reduction in lattice parameters is observed as the Al+3 doping level increases. This can be attributed to the short ionic radii of Al+3 ions (0.535 Å) compared to Fe+3 ions (0.645 Å). The obtained c/a ratio falls within the acceptable range of 3.98. Consequently, the formation of magnetoplumbite structure is also confirmed. The SEM image reveals the uniform distribution of particles. The exchange of Fe+3 ions with coercive Al+3 ions led to a decline in saturation magnetization Ms and a significant increase in the coercivity Hc. The magnetic moment mB and Mr of hexaferrites exhibit a decline when Al ions are introduced. This reduction can be ascribed to several factors: the substitution of non-magnetic Al3+ ions in place of Fe3+ ions, the spin-canted ordering of Fe3+ ions, and the valency of Fe ions from 3+ to 2+.

Modulation of magnetic and dielectric properties by Al3+ substitution in Ca3CoMnO6 ceramics

We report a detailed study of the influence of non-magnetic Al3+ doping on the microstructure, magnetic, and dielectric characteristics Ca3CoMnO6. The introduction of Al3+ leads to the suppression of competing short-range magnetic orders, a gradual disappearance of the spin freezing peak in Ca3CoMn1-xAlxO6 was observed, accompanied by the release of magnetic frustration. Moreover, a weakening of the antiferromagnetic order in Ca3CoMnO6 was attributed to the dilution effect induced by non-magnetic Al3+ within the Co-Mn-Co-Mn spin chains. The dielectric measurements exhibit excellent agreement with the magnetic measurements. The substitution of Mn4+ with Al3+ results in the attenuation of relaxor ferroelectric behavior, accompanied by a decrease in the static freezing temperature Tf and an increase in the activation energy Ea. It indicates that Al3+ substitution could well suppress the formation of polar nanoregions. With introducing Al3+ the magnetodielectric effect of Ca3CoMnO6 is also significantly enhanced. For the x = 0.15 sample, the magnetodielectric effect undergoes a notable variation of approximately 10 % under a magnetic field of H = 4 T.

Structure and properties of fiber-reinforced LiZn ferrite ceramics prepared via spark plasma sintering

In order to improve the matrix cracking of LiZn ferrite (LZF) ceramics during spark plasma sintering, fiber-reinforced LZF materials were prepared using silicon carbide nanofibers (SCFs) and alumina whiskers (AWs) as reinforcement phases. The effect of fiber reinforcement on the microstructure and mechanical, electrical, and magnetic properties of LZF was systematically studied. The results reveal that SCFs lead to an increase in grain size of SCF-reinforced LiZn ferrites (LZF-S) and a deterioration of grain morphology due to the transgranular behavior of SCFs. The increase in complex dielectric constant and dielectric loss, as well as the decrease in resistance of LZF-S, is due to the increase in Fe2+ concentration in ceramics and low resistance of SCFs. AW-reinforced LiZn ferrites (LZF-A) show the opposite effect due to the high porosity caused by AWs and the high resistance of AWs. LZF-S exhibits high fiber/matrix bonding strength, which permits the transfer of the load from the matrix to the fiber to be more effective, leading to a high fracture toughness (KIC) of 5.1 MPa m1/2. The bonding strength between fiber and matrix of LZF-A is low, but a large number of pores passivate the crack tip. At an SCF content of less than 2.5 wt%, the saturation magnetization (Ms) of LZF does not decrease obviously, but a small amount of AWs leads to a significant decrease in Ms (pure LZF: 83 emu·g−1; 1.0 wt% SCFs: 80 emu·g−1; 1.0 wt% AWs: 62 emu·g−1), which can be ascribed to the partial substitution of Fe3+ by nonmagnetic Al3+ ions. When the content of reinforcement phases is 1 wt%, the ferroresonance linewidth increases significantly due to the high porosity caused by the secondary phases (pure LZF: 234 Oe; 1.0 wt% SCFs: 2161 Oe; 1.0 wt% AWs: 1020 Oe).

High performance of Co-free LiNixMn1-xO2 cathodes realized by nonmagnetic ion substitution for Li-ion batteries

Ni-rich LiNixMn1-xO2 cathodes have been extensively probed to resolve the electrochemical performance degradation in the absence of Co3+ compared to LiNixCoyMn1-x-yO2 cathodes for lithium-ion batteries. Herein, LiNi0.6Mn0.4O2 (NM64) and a series of nonmagnetic Al3+ ions substituted NM64 cathode materials are designed and prepared via a sol–gel route. It is found that the inferior electrochemical performance of NM64 derives from the magnetic frustration arising from Mn ions and the unstable Mn3+ ions, which will lead to severe Li/Ni mixing, and weak structural and interfacial stabilities of the cathode. The superconducting quantum interference device (SQUID) analysis proves that the nonmagnetic Al3+ ion can lower the Li/Ni disorder in NM64 cathode by relieving magnetic frustration. Moreover, the dQ/dV and XPS analyses confirm that both structural and interfacial stabilities are enhanced for NM64 cathode owing to Al3+ substitution, contributing to fewer byproducts after a long cycle. Consequently, LiNi0.582Mn0.388Al0.03O2 cathode delivers a high discharging capacity of 179 mAh g−1 at 1.0C with a capacity retention of 87.6% after 100 cycles. This study not only gives an in-depth understanding of the mechanism of electrochemical performance degradation for NM64 cathode, but also demonstrates an efficient solving approach through Al3+ complementary substitution.

Irreversible metamagnetic behaviors and H-T phase diagram in phase separated La0.5Ca0.5Mn1-xAlxO3-δ

Magnetization relaxation, ac susceptibility, dc magnetization and magnetoelectrical transport measurements have been carried out on Al3+-doped manganites La0.5Ca0.5Mn1-xAlxO3-δ (x = 0.05, 0.07, 0.09, 0.10, 0.15). Experimental results suggest that nonmagnetic Al3+ substituting Mn suppresses the ferromagnetic phase and induces a charge ordered antiferromagnetic phase. The coexistence and competition of these two kinds of interactions result in a spin-glass like state in x = 0.1 and 0.15 system. Obvious hysteresis was observed in both magnetization and resistivity versus temperature and magnetic field curves, suggesting an inhomogeneous metastable phase transition. Upon applying a magnetic field of HCA-F, the Al3+-doped samples undergo an irreversible metamagnetic transition from the charge ordering antiferromagnetic insulating to ferromagnetic metallic phase in the low temperature region. Phase diagram in the HC-T plane has been determined according to the magnetization and magnetoelectric transport measurements. The magnetic disorders and antiferromagnetic matrix produced by Al3+ dopants and spontaneous oxygen vacancies play an important role in the pinning of the FM phase.

Solution combustion route for Ni and Al co-doped lithium ferrite nanoparticles: Synthesis, the effect of doping on the structural, morphological, optical, and magnetic properties

Nickel and Aluminum co-doped Lithium Ferrite Nano-particles, (Li1-xNi0.5xAlxFe1-xO2), (0 ≤ x ≤ 0.3) are synthesized through the solution combustion route with the fuel urea as a reducing agent. The prepared Nano-particles at different doping concentrations are investigated using several tools. The thermal analysis thermographs revealed a combustion reaction at around 300 °C. Doping lithium ferrite with different concentrations changes the structural, morphological, optical, and magnetic characteristics significantly. The increase of the lattice constant to 5.8 Å, and the decrement of the crystallite sizes can be related to the differences in the ionic radius of the incorporated elements, and the increment of Al content. Additional induced sub-band gap energy levels as a result of the numerous surface and interface defects in the nanoparticle structure result in a modest narrowing of the band gap (direct and indirect). The associate shift of the band gap with the decrement of the crystallite size can be attributed to the quantum confinement effect as a result in the tiny size regime. The reduction of the sample's disorder structure and the creation of pure phases were both credited with increasing the saturation magnetization of the undoped sample, but the saturation magnetization decreased when magnetic Fe3+ ions are replaced by nonmagnetic Al3+ ions. The optically active and soft ferrite nanoparticles were confirmed by the behaviour of the physical parameters before them. The synthesized nanoparticles are considered as promising materials for nonlinear optics and memory recording applications.

Fragmented ferromagnetic-phase and evolution of Re-entrant cluster-glass behavior in La0.6Sr0.4Co1-xAlxO3 (0 ≤ x ≤ 0.15) compounds

We have observed the fragmentation of ferromagnetic-phase with Al3+ substitution in polycrystalline La0.6Sr0.4Co1-xAlxO3 (0 ≤ x ≤ 0.15) perovskite compounds. The introduction of non-magnetic Al3+ ions at the Co3+ sites results in several segregated ferromagnetic domains that interact and demonstrate cluster-glass-like behavior. The structural information and phase purity is determined with X-ray diffraction and Rietveld-refinement. The compounds crystallize in the R-3c space group with some iso-structural distortions. The soft X-ray absorption spectroscopy (SXAS) of cobalt L2,3-edges revealed the heterogeneous electronic phase with a majority of Co3+ ions. The spin-only contribution of Co3+ and Co4+ to the net-effective magnetic moment confirms the presence of High-spin Co3+ (S = 2) and Low-spin Co4+ (S = 1/2) ionic species. The magnetization parameters (θp, Tc, Tb, C, and μeff) observed from the (FC-ZFC) dc-magnetization measurements were suppressed with increasing Al3+ concentration. Inhomogeneous magnetic-phase transition is observed due to segregation in the ferromagnetic phase. Hence, in the parent compound, the intrinsic-ferromagnetism weakens with Al3+ substitution. Therefore, the long-range ferromagnetic-ordering fragments into several interacting FM clusters are isolated by a coexisting non-ferromagnetic (Al3+ rich) sub-lattice. The frequency-dependent magnetic ac-susceptibility measurements determine a re-entrant cluster-glass nature which is analyzed with the Mydosh parameter (φ), Critical-Slowing-down of spins, and Vogel-Fulcher-formulation.

Chemical pressure-induced structural, optical, and magnetic property transformations of PrAlO3

Progressive substitution of non-magnetic Al3+-ion with magnetic Cr3+-ion in PrAlO3 has been carried out in the present study by preparing the samples using the epoxide mediated sol-gel method. Extensive characterization of these samples was performed to comprehend the effect of chemical pressure on the structure and optical and magnetic properties. The hexagonal system of PrAlO3 with rhombohedral symmetry (R-3c space group) was preserved up to 60 mol % inclusion of Cr3+ in place of Al3+, beyond which the samples exhibited orthorhombic symmetry (Pnma space group). FTIR and Raman's spectra also confirmed the symmetry reduction in these samples. The transitions associated with Pr3+ and Cr3+ ions were observed in the optical spectra. The optical bandgap estimated using Tauc plot decreased from 3.2 (x = 0.10) to 1.75 eV (x = 0.60) in PrAl1-xCrxO3. With higher Cr3+-concentrations, the optical bandgap increased from 1.75 (x = 0.70) to 3.2 eV (PrCrO3). The field-dependent magnetic measurements indicated that all the samples were paramagnetic at room temperature and ferromagnetic at 2 K. Inclusion of Cr3+ -ion in place of Al3+ -ion in PrAlO3 shifts the transition from 109 to 231 K. They resulted in the increased effective magnetic moment.

Aluminum Doping and Nanostructuring Enabled Designing of Magnetically Recoverable Hexaferrite Catalysts.

We demonstrate an approach based on substituting a magnetic cation with a carefully chosen isovalent non-magnetic cation to derive catalytic activity from otherwise catalytically inactive magnetic materials. Using the model system considered, the results illustratively present that the catalytically inactive but highly magnetic strontium hexaferrite (SrFe12O19; SFO) system can be transformed into a catalytically active system by simply replacing some of the magnetic cation Fe3+ by a non-magnetic cation Al3+ in the octahedral coordination environment in the SFO nanocrystals. The intrinsic SFO and Al-doped SrFe12O19 (SrFe11.5Al0.5O19; Al–SFO) nanomaterials were synthesized using a simple, eco-friendly tartrate-gel technique, followed by thermal annealing at 850 °C for 2 h. The SFO and Al–SFO were thoroughly characterized for their structure, phase, morphology, chemical bonding, and magnetic characteristics using X-ray diffraction, Fourier-transform infrared spectroscopy, and vibrating sample magnetometry techniques. Catalytic performance evaluated toward 4-nitrophenol, which is the toxic contaminant at pharmaceutical industries, reduction reaction using NaBH4 (mild reducing agent), the Al-doped SFO samples exhibit a reasonably good performance compared to intrinsic SFO. The results indicate that the catalytic activity of Al–SFO is due to Al-ions occupying the octahedral sites of the hexaferrite lattice; as these sites are on the surface of the catalyst, they facilitate electron transfer. Furthermore, surface/interface characteristics of nanocrystalline Al–SFO coupled with magnetic properties facilitate the catalyst recovery by simple, inexpensive methods while readily allowing the reusability. Moreover, the activity remains the same even after five successive cycles of experiments. Deriving the catalytic activity from otherwise inactive compounds as demonstrated in the optimized, engineered nanoarchitecture of Al-doped-Sr-hexaferrite may be useful in adopting the approach in exploring further options and designing inexpensive and recyclable catalytic materials for future energy and environmental technologies.

Investigation of structural, magnetic and electrical properties of aluminum substituted Co-Mg ferrite

The effect of nonmagnetic Al3+ substitution on the structural, morphological, magnetic, and dielectric characteristics of Co0.5Mg0.5AlxFe2−x04 ferrite nanoparticles synthesized using the co-precipitation method was investigated. All samples were found to have a single-phase cubic spinel by X-ray diffraction. The decrease in crystallite size from 55 to 29 nm with Al3+ substitution validated the materials nano-crystalline formation. The infrared spectrum exhibits two distinct absorption bands matching to the spinel structure as well as two extra absorption bands and a shoulder between 360 and 265 cm−1. The DSC exothermic peaks around 440 °C may be attributed to the phase shift of the prepared samples from amorphous to the crystalline state. The TEM results were used to investigate the sample shape and quantify particle size demonstrating that increasing the Al3+ content induces a decrease in particle size. The VSM technique revealed a decrease in magnetic properties which was attributable to an increase in nonmagnetic Al3+ ions. The magnetic permeability is found to rise with increasing Al3+ content as the anisotropy constant decreases. Dielectric characteristics were investigated at room temperature in the frequency range of 0.1 Hz–20 MHz. The presence of polaron type conduction in the prepared samples was confirmed by the ac conductivity. These produced nanoparticles dielectric characteristics demonstrate their utility in high-frequency device development applications and electronic device production.

Enhancement of electrical and magnetic properties of Al3+ substituted CuZn nano ferrites with structural Rietveld refinement

Nanoparticles of Cu0.65Zn0.35AlxFe2-xO4 (x = 0.00 to 0.10, in the step size of 0.025) were synthesized by employing the auto-combusted sol–gel process and annealed at 700 ˚C. The effect of Al3+ substituted Cu-Zn mixed nanoferrites on the structural, magnetic, dielectric, and electrical properties has been investigated. The behavior of the structural exploration of these compositions has been implemented by the X-ray diffraction technique and further refined through the Rietveld refinement technique which provides structural homogeneity parameters like crystal structure, crystallite size and cation distribution. The surface morphology revealed the existences of spherical shape nano-grains with narrow size distribution. Dielectric properties display reduction in space charge polarization with Al3+ content. From the electric modulus analysis, broader semicircles are obtained by the substitution of Al3+ in our parent compound. The addition of upto 5% Al content shows increment of both grain (Rg) and grain boundary resistance. Enhancement of Rg contribution with Al3+ content at high frequency region reduced eddy current losses remarkably. The rising trend of σac depicts the normal nature of the investigated materials with frequency, which is clarified by the electron hopping mechanism. The saturation magnetization (Ms) increased with nonmagnetic Al3+ substitution up to x =0.075 and upon application of Law of Approach to Saturation various hysteresis parameters like Ms, anisotropy constant are obtained.

Effects of co-substitution of Al3+ and Cr3+ on structural and magnetic properties of nano-crystalline CoFe2O4 synthesized by the sucrose technique

Al–Cr substituted CoFe2O4 nano spinels (CoAlxCrxFe2−2xO4 where x = 0.1 to 0.6) were successfully prepared for the first time via sucrose sol–gel auto-combustion technique. The structural parameters as well as magnetic and electrical properties of the prepared ferrites have been investigated. X-ray diffraction (XRD) confirmed single-phase formation and showed a decrease in the calculated values of lattice parameters by substitution attributed to the difference in the ionic radii. Based on the obtained structural parameters, an appropriate cation distribution was proposed and discussed. In this distribution, most of Al3+ and Cr3+ ions preferred octahedral sites occupation however, small amount of Al3+ seek the tetrahedral sites. Accordingly, the magnetic characterization via vibrating sample magnetometer (VSM) measurements revealed a decrease in the saturation magnetization (Ms) by successive substitution from 57.9 to 4.7 emu/g, indicating the incorporation of non-magnetic Al3+ and anti-ferromagnetic Cr3+ ions in the octahedral sites instead of Fe3+ ions. The much lower magnetization values obtained than that prepared by other methods could be attributed to the present lower sizes. The coercivity measurements indicated soft ferrimagnetic properties favoring their uses as high frequency transformers. Ac-conductivity as well as dielectric properties, as a function of frequency and temperature, indicated semiconducting behavior with decreasing trend by Al–Cr substitution due to decreasing in the Fe3+-Fe2+ hopping probability in octahedral sites. The obtained results suggest the using of the present materials in electronic inductors, electromagnets and transformers and microwave devices.

Effect of Electron Doping on the Crystal Structure and Physical Properties of an n = 3 Ruddlesden–Popper Compound La4Ni3O10

The physical properties of La4Ni3O10 with a two-dimensional (2D)-like Ruddlesden–Popper-type crystal structure are extraordinarily dependent on temperature and chemical substitution. By introducing Al3+ atoms randomly at Ni sites, the average oxidation state for the two nonequivalent Ni cations is tuned and adopts values below the average of +2.67 in La4Ni3O10. La4Ni3–xAlxO10 is a solid solution for 0.00 ≤ x ≤ 1.00 and is prepared by the citric acid method, with attention paid to compositional control and homogeneity at low Al level (x) concentrations. The samples adopt a slightly distorted monoclinic structure [P21/a (Z = 4)], evidenced by peak broadening of the (117) reflection. We report a remarkable effect on the electronic properties induced by tiny amounts of homogeneously distributed Al cations, with clear correspondence between resistivity, magnetization, diffraction, and density functional theory (DFT) data. DFT shows that electronically, there is no significant difference between the nonequivalent Ni atoms and no tendency toward any Ni3+/Ni2+ charge ordering. The resistivity changes from metallic to semiconducting/insulating with increasing band gap at higher Al levels, consistent with results from DFT. The metal-to-metal (M-T-M) transition reported for La4Ni3O10, which is often interpreted as a charge density wave, is maintained until x = 0.15 Al level. However, the temperature characteristics of the resistivity change already at very low Al levels (x ≤ 0.03). A coupling of the M-T-M transition to the lattice is evidenced by an anomaly in the unit cell dimensions. Moreover, there is an excellent correlation between the resistivity and magnetization data shown by the metallic and Pauli paramagnetic regime for La4Ni3–xAlxO10 with x < 0.25. The introduction of the fixed +3 oxidation state of Al atoms randomly at the Ni sites reduces the overall oxidation state of Ni2.67+ by keeping the oxygen stoichiometry unchanged. In addition, the nonmagnetic Al3+ for Ni is likely to block Ni–O–Ni exchange pathways through −Ni–O–Al–O–Ni– fragments into the network of corner-shared octahedra with the emergence of possible short-range ferromagnetic ordering of the ferromagnetic domains/clusters that are formed due to Al substitutional disorder in a paramagnetic insulating matrix.

Structure and magnetic properties of a class of spinel high-entropy oxides

A class of high-entropy spinel oxides system, (Al,Cr,Fe,Mn,Ni)3O4, (Co,Cr,Al,Mn,Ni)3O4, (Co,Cr,Fe,Al,Ni)3O4, (Co,Cr,Fe,Mn,Al)3O4, (Co,Cr,Fe,Mn,Ni,Al)3O4 nanocrystalline powders, have been prepared by the solution combustion synthesis method with the temperature at 550 °C, 650 °C, and 750 °C. The phase composition analysis of the samples shows that all samples are single-phase spinel structure (Fd-3 m) and the crystalline size and lattice constant increase as temperature goes up. Furthermore, magnetic hysteresis loops indicate that magnetic moment and crystallite size can be controlled through non-magnetic Al3+, making it possible to achieve tailorable magnetic property. XPS results show that in all HEOs, the valence of Fe is + 3, the valence of Co is + 8/3 (+2: +3 = 1:1), the valence of Ni is + 2, the valence of Cr is + 3, the valence of Mn is + 3. The magnetic difference between the HEOs is caused by element substitution.

Influence of variation of structural parameters on magnetic properties of Al-substituted Ni spinel ferrite

It is very important to study the structural properties of the material to understand the physical properties. According to suggested cations distribution of Ni–Al ferrite as the formula $$({\text{Fe}}_{1 - t}^{3 + } {\text{Al}}_{t}^{3 + } )\left\{ {{\text{Ni}}^{2 + } {\text{Al}}_{x - t}^{3 + } {\text{Fe}}_{1 - x + t}^{3 + } } \right\}{\text{O}}_{4}^{2 - }$$ , with ( $$0.0 \le x \le 0.5$$ ) and ( $$0.0 \le t \le 0.1$$ ), the structural parameters were studied. The cations radii of tetrahedral ( $$R_{{\text{T}}}$$ ) did not change, but octahedral ( $$R_{O}$$ ) sites decreased with increasing Al3+ ions. Lattice constants ( $$a_{{{\text{th}}}}$$ ) decreased with increasing Al content. The values of $$u^{{\overline{4}3m}}$$ changed over the ranged 0.3818538155, whereas the values of $$u^{{\overline{3}m}}$$ varied from 0.25685 to 0.25655. With increasing Al content, M–M lengths decreased, in addition, the bond lengths q, r, and s decreased except p. In addition, with increasing Al3+ ions, $$\theta_{1}$$ , $$\theta_{2}$$ , and $$\theta_{5}$$ decreased but $$\theta_{3}$$ and $$\theta_{4}$$ increased. $$d_{{{\text{TE}}}}$$ and $$d_{{{\text{TL}}}}$$ were constant, whereas $$d_{{{\text{OEu}}}}$$ , $$d_{{{\text{OL}}}} ,$$ and $$d_{{{\text{OE}}}}$$ decreased with increasing Al3+ ions. $$L_{{{\text{T{-}T}}}}$$ , $$L_{{{\text{O{-}O}}}} ,$$ and $$L_{{{\text{T{-}O}}}}$$ reflected the same behavior as that of $$a_{{{\text{th}}}}$$ , where they decreased with increasing Al3+ ions concentration. As a result, the incorporation of non-magnetic Al3+ ions into the given ferrite system reduces the strength of the magnetic interactions, which relates to the changing on structural parameters.

Effect of Ni and Al substitution on the magnetic properties of Y-type hexaferrite Ba0.5Sr1.5Zn0.5Ni1.5Fe11.92Al0.08O22 powders

The effect is reported of substituting the non-magnetic Zn2+ cations with magnetic Ni2+ cations, and of the magnetic Fe3+ cations with non-magnetic Al3+ cations in Ba0.5Sr1.5Zn0.5Ni1.5Fe11.92Al0.08O22 on the resulting magnetic properties. The Y-type hexaferrite powders were synthesized by citric acid sol-gel auto-combustion, followed by appropriate thermal annealing. The saturation magnetization values (Ms ) in a magnetic field of 50 kOe were 36 emu/g and 30 emu/g at 4.2 K and 300 K, respectively. The zero-field-cooled (ZFC) and field-cooled (FC) magnetization vs. temperature (4.2 – 300 K) were measured in dc magnetic fields of 50 Oe, 100 Oe and 500 Oe. The changes resulting from the dissimilar cationic substitutions were identified and discussed.