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We prepared ultrafine MnCo 2 O 4 particles using a facile sol–gel autocombustion method. The structural and vibrational characterizations confirmed the formation of a pure cubic spinel phase in as-synthesized MnCo 2 O 4 particles. The surface morphology analyses revealed the porous structure with an average particle size of 5 nm and uniform distribution of manganese (Mn), cobalt (Co), and oxygen (O) in the particles. We observed the presence of multiple valence states of Mn and Co, occupying both tetrahedral and octahedral sites, enhancing our insight into the material's electronic properties and structural configuration. Our magnetization studies unveiled a Curie Temperature (T C) of 185 K with ferrimagnetic ordering below T C , resulting in substantial magnetization (9.8 emu/g) and coercivity (3.46 kOe) at 2 K and weak magnetic behavior above T C. This is attributed to the finite size and surface effects. Furthermore, the incorporation of MnCo 2 O 4 nanoparticles and graphene oxide into a polyurethane foam matrix resulted in an excellent sound absorption coefficient of 90 % at 2000 Hz. This outstanding acoustic performance underscores the versatile applications of MnCo 2 O 4 nanoparticles in diverse noise mitigation applications. [Display omitted] [ABSTRACT FROM AUTHOR]

In the present work, [Co (1-(x + y)) Mg x Ni y ][Cr 2 ]O 4 (CMNCr)(where, x = y = 0, 0.10, 0.20) NPs are examine in detail by using experimental results. Solution combustion method is adopted to prepare the CMNCr NPs. Experimental results were studied to understand structure (using XRD), microstructure (using SEM) and magnetic behaviour (using SQUID). The structural analysis was confirmed a single-phase spinel cubic structure with singular structural distortions associated with Mg–Ni doping and the generation of metal vacancies. SEM micrographs of all samples reveal their highly porous nature. EDS was utilized to examine the elemental analysis of the samples. The formation of spinel cubic structure without impurity were also confirmed by Fourier-transform infrared (FTIR) spectroscopy and the same tool is used to investigate the absorption bands related to the A-site and B-site. For all samples, paramagnetic phase to ferrimagnetic phase transition observed at T C and conical spiral spin order transition observed at T S. The curie temperature is found to be 98 K, 89 K, and 85 K for [Co][Cr 2 ]O 4 , [Co 0.8 Mg 0.1 Ni 0.1 ][Cr 2 ]O 4 and [Co 0.6 Mg 0.2 Ni 0.2 ][Cr 2 ]O 4 samples, respectively. The spiral transition temperature is found to be 26 K, 14 K and 8 K for [Co][Cr 2 ]O 4 , [Co 0.8 Mg 0.1 Ni 0.1 ][Cr 2 ]O 4 and [Co 0.6 Mg 0.2 Ni 0.2 ][Cr 2 ]O 4 samples, respectively. All of the samples exhibit paramagnetic behaviour above T C. The negative magnetization effect were observed in [Co 0.6 Mg 0.2 Ni 0.2 ][Cr 2 ]O 4 NPs. 20% of Mg and 20% of Ni substitution to Co site in [Co][Cr 2 ]O 4 leads to the evident magnetization reversal at the compensation temperature with an applied magnetic field of 100 Oe. The M − H loop at 10 K exhibits large coercivity due to the spiral spin ordering. This phenomenon of negative magnetization in the material results in a stable state of magnetization in the material, which has significant applications in the field of magnetic storage devices. [ABSTRACT FROM AUTHOR]

We prepared pure-phase Ni x Mn 1-x Co 2 O 4 (x = 0, 0.25, 0.5, 0.75 and 1) nanoparticles using a low-temperature solid-state reaction method. Magnetization measurement results showed that with Ni doping, the Curie temperature and coercivity of Ni x Mn 1-x Co 2 O 4 increased. Multiple magnetic phases that transition from paramagnetic to ferrimagnetic to ferrimagnetic and antiferromagnetic were observed to coexist in the Ni 0.5 Mn 0.5 Co 2 O 4 sample. At low temperatures, the ferromagnetic and antiferromagnetic phases coexist in Ni x Mn 1-x Co 2 O 4 (x = 0 and 0.25), and as the concentration of Ni increases, Ni x Mn 1-x Co 2 O 4 (x = 0.75 and 1) show a spin glass state. The structure of Ni x Mn 1-x Co 2 O 4 (x < 0.5) is mainly affected by cation defects, and by cation substitution when x is greater than 0.5. The results of first-principles calculations show that covalent bonds exist in Ni x Mn 1-x Co 2 O 4 and that the strength of the Ni-O bond is greater than that of the Mn-O bond. [ABSTRACT FROM AUTHOR]

A detailed study has been carried out of the static and dynamic magnetic properties of ferrimagnetic spinel MgFe 1.2 Ga 0.8 O 4 nanoparticles (NPs), including the measurements of low-field dc -magnetization M (T) under zero-field-cooled (ZFC) and field-cooled (FC) conditions and ac -susceptibility χ ac (T) at different frequencies (f) and amplitudes of the ac -field (H ac). Below, a Curie temperature (T C), a clear magnetic irreversibility (M ZFC (T) ≠ M FC (T)), as well as a broad peak in both M ZFC (T)– M FC (T) magnetizations have been observed. At T ≪ T C , the two distinct, frequency-dependent peaks at T p1 ≈ 9 K and T p2 ≈ 14 K in the imaginary part of the ac -susceptibility χ ac '' (T) have been found. Their positions have been consistent with those of the anomalies detected on the temperature dependence of the magnetic contribution to the heat capacity C mag (T), and a sharp decrease of the M ZFC (T) magnetization near ≈ 10–20 K. It was revealed that the fitting of the frequency dependence of the peaks' positions (T p1 (f) and T p2 (f)) in the imaginary part of ac -susceptibility χ ac '' (T) using the Neel-Arrhenius law yields unphysical values of the relaxation time (τ 0) and, therefore, these results ruled out a possibility of an existence of superparamagnetic (SPM) clusters in the system. On the other hand, the T p1 (f) and T p2 (f) dependences followed both the Vogel-Fulcher law and the power law. These observations indicate that, a complex magnetic state in MgFe 1.2 Ga 0.8 O 4 , realized in the low temperature region, may likely be related to a progressive freezing of magnetic clusters. [ABSTRACT FROM AUTHOR]

Abstract A series of Co 0.5-x Ni x Zn 0.5 Fe 2 O 4 (x = 0–0.25 insteps of 0.05) nano crystalline ferrites were synthesized in combustion method using citric acid as fuel. Densities and porosities were calculated using the lattice constant and Archimedes's principle. A linear increase in experimental density and a decrease in porosity were observed with increase in nickel concentration. Cationic distribution was proposed on the basis of theoretical lattice constant and it was correlated with the variation in magnetic and electrical properties of all samples. TEM image of the sample with nickel concentration x = 0.15 indicated the existence of nano-metric range particles and the sample was characterized with the help of inter-planar spacing(s) from SAED pattern. Morphological and surface analysis was studies using Scanning Electron Microscopy and well developed nearly spherical grains were observed with increase in nickel concentration. Energy Dispersive Spectroscopic (EDS) analysis was performed for all nickel substituted samples and all displayed stoichiometric proportions of ions in the samples as per the chemical composition. Elemental mapping was done for all samples using EDS data. Curie temperature was dropped nearly 90 °C at the end of the series. Initial permeability showed slight variation with an increase in nickel concentration and it remained nearly constant with frequency up to 3 MHz. Magnetic loss was observed to be constant for all samples after 100 kHz. DC Electrical resistivities of all samples were measured and all samples displayed resistivity in the order of 108 Ω-cm. AC resistivity and dielectric studies were conducted from 100 Hz to 5 MHz for all samples. Dielectric constant and losses of all samples exhibited very low values compared to that of conventional ferrites. The electrical properties of all samples were discussed with the help of temperature variation of resistivity, activation energy, grain size, density and porosity. [ABSTRACT FROM AUTHOR]

The magnetic and magnetocaloric properties of the Th 6 Mn 23 -type structure Gd 6 (Mn 1−x Co x ) 23 (x ≤ 0.3) compounds are investigated from DC magnetization measurements. The Curie temperature of these ferrimagnetic materials evolves non-continuously with the Co content from T C = 489 K for x = 0 to T C = 118 K for x = 0.3. In relation with the lower magnetic moment of Co atoms compared with that of Mn atoms, the Co to Mn substitution leads to a decrease of the maximal magnetization, recorded at 5 K in an applied magnetic field of 9 T, from 54.7 μ B /f.u. for x = 0 to 36.3 μ B /f.u. for x = 0.3. These materials present an anomalous magnetocaloric effect, characterized by two broad –ΔS M maxima of moderate magnitude at T C and around 100 K, yielding to wide magnetocaloric response from T C down to the lowest temperature, and consequently, a relatively large cooling capacity q 10–350K (μ 0 ΔH = 5 T) reaching ∼ 3.7 J cm −3 for Gd 6 (Mn 0.875 Co 0.125 ) 23 . The results are analyzed and discussed in connection with previously published data. [ABSTRACT FROM AUTHOR]

Bulk (Mn 1- x Co x ) 2 VAl ( x = 0, 0.25, 0.50) alloys in highly ordered L 2 1 structure with a very small amount of B 2 disorder have been prepared and their magnetic properties have been measured. The value of saturation magnetizations of the alloys with x = 0, 0.25 and 0.50 are 1.88 μ B , 0.84 μ B and 0.07 μ B , respectively, being consistent with 2.00 μ B , 1.00 μ B and 0 μ B , respectively, predicted by the Slater–Pauling rule. This indicates that the stoichiometric MnCoVAl alloy is a fully compensated ferrimagnet (FCF). Spin polarization measurements using point contact Andreev reflection technique showed that the quaternary alloys exhibited higher intrinsic spin polarization than the parent ternary composition. The spin polarization of 0.60 deduced for the MnCoVAl alloy suggests that spin-polarized current can be extracted from FCF. Curie temperature ( T C ) and the effective anisotropy constant of (Mn 1- x Co x ) 2 VAl alloys decrease with increase in Co content. [ABSTRACT FROM AUTHOR]

We systematically study the stability, Gilbert damping parameters, electronic structure, exchange interaction and Curie temperature of CrYCoZ (Z = Al, Ga, In, Tl) alloys. Stability is estimated from the perspective of thermodynamics, dynamics and mechanics. Gilbert damping parameters are calculated by using the linear response formalism, and the values 0.6 ∼ 4. 1 × 10−3 are observed at room temperature. Electronic calculations show that the CrYCoZ alloys are half-metallic ferrimagnets, and their integer magnetic moments follow the M t = Z t − 18. Origin of gap is discussed by the hybridization, distribution and occupation of electronic states as well as the charge transfer. In addition, the effect of GGA+U on electronic structure is also discussed. Based on the Heisenberg model, we calculate the exchange interactions between atomic components, and analyze the competition and collaboration between d – d exchange, super-exchange and RKKY exchange, finally offer the dominant mechanism of appearance of ferrimagnetic order phase. Furthermore, we calculate the Curie temperatures of CrYCoZ alloys, which are much higher than room temperature. Overall, the CrYCoZ alloys can be considered as a prospective candidates in spintronics application. [Display omitted] • Stability of CrYCoZ is estimated in terms of thermodynamics, dynamics and mechanics. • Gilbert damping parameters of CrYCoZ alloys are 0.6 ∼ 4.1 × 10−3 at room temperature. • The CrYCoZ alloys are half-metallic ferrimagnets. • Total magnetic moments of CrYCoZ alloys obey the Slater–Pauling rule M t = Z t − 18. • Curie temperatures of CrYCoZ are higher noticeably than room temperature. [ABSTRACT FROM AUTHOR]

The GdTi 0.05 Fe 0.95- x Mn x Si, х = 0–0.95 intermetallic compounds with a tetragonal crystal structure of the CeFeSi type (space group P4/nmm, N 129, tP6) have been studied. The lattice parameter c and the Curie temperature T C increase quickly, whereas the lattice parameter a is almost unchanged in the system when the content of Mn increases. The saturation magnetization, magnetocaloric effect MCE and refrigerant capacity RC change non-monotonically with a dip at intermediate compositions that is presumably due to the canted ferrimagnetic structure of these compounds. The MCE and RC vary in a field changing to 17 kOe within the small ranges of 1.6–2.7 J/kgK and 60–117 J/kg around T C , respectively, while T C changes in a wide range around the room temperature from 160 to 360 K. • The lattice parameter c and T C increase and lattice parameter a is almost unchanged. • Presumably, the canted ferrimagnetic structure is formed in the system. • М sat. , MCE, RC change non-monotonically with a dip at intermediate compositions. • MCE, RC , T C vary in the ranges 1.6–2.7 J/kgK, 60–117 J/kg at 17 kOe field, 160–360 K. [ABSTRACT FROM AUTHOR]

In this work, structural, electronic and magnetic properties of Ni doped ZnO nanoparticles (NP's) synthesized via the sol-gel method have been investigated. Different techniques of characterization have been applied to study the Ni dependence of the microstructural, morphological, compositional and magnetic properties. As a result, X-ray diffraction analysis indicates that the obtained samples have a hexagonal Wurtzite structure with preferential orientation along (101). The increase of Ni concentration leads to a size reduction of the nanoparticles. Also segregated Ni clusters have been observed by SEM/EDX. The magnetization field (M − H) curves reveal the existence of ferromagnetism in Ni-doped ZnO at room temperature. First principle calculations based on density functional theory are applied to study the effect of Ni doping on the structural, electronic and magnetic properties of ZnO, allowing for a deeper understanding for the experimental findings. The obtained results indicate that Ni doped ZnO with less than 8.33% Ni present long-range ferromagnetic ordering. Furthermore, Ni doped ZnO is antiferromagnetically stable at 12.5%. Monte Carlo simulation based on heat bath algorithm coupled with DFT results have been used to validate the proposed explanation for the magnetic behavior of the experimental part. Therefore, the obtained results indicate that Ni doped ZnO is a good candidate as a diluted magnetic semiconductor due to its high exchange coupling interaction that leads to a high Curie temperature. • Magnetic properties of Ni doped ZnO NP's have been explored experimentally and theoretically. • Reduction of the crystallite size has been observed. • Ni doped samples exhibit ferromagnetic properties at room temperature. • Ni doped ZnO with less than 8.33% of dopant presents a long-range magnetic ordering. • Monte Carlo simulation shows that Ni doped ZnO presents a Curie temperature above the room temperature. [ABSTRACT FROM AUTHOR]

The local crystal structure alterations in the tetrahedral positions of the hausmannite Mn 3 O 4 structure by Co2+ ions and its consequence on the magnetic ordering are studied in detail. The cation composition, bond distance and bond angle of the Co x Mn 3-x O 4 series (x = 0.0. 0.1, 0.3 and 0.5) is determined by XRD Rietveld refinement. The charge state of the elements Co, Mn and O are investigated using XPS measurements, which confirm the bivalent cobalt ion occupation in the tetrahedral lattice. Considerable reduction in tetrahedral and axial octahedral bonds with the introduction of Co2+ ions dramatically increased the Curie temperature (T C) from 43 K (Mn 3 O 4) to 62 K (Co 0.5 Mn 2.5 O 4). The Lotgering-Srinivasan-Seehra model is employed to study the canted spin arrangement and the exchange interactions of Co 0.5 Mn 2.5 O 4. The presence of cluster glass transition at T P = 42 K in Co 0.3 Mn 2.7 O 4 is well-established through the AC susceptibility measurements and it is further substantiated by Vogel-Fulcher law and dynamic scaling power law. The origin of the cluster glass state is confirmed by the calculated strong geometric frustration factor (f = 19.5), due to the inhomogeneous distribution of cobalt ions in the intermediate concentrations. Field cooled isothermal magnetic measurements corroborated the exchange bias phenomenon in the Co 0.3 Mn 2.7 O 4 sample, because of the interaction between ferrimagnetic-cluster glass phases occurring below the spin freezing temperature T P. Image 1 • The reduction in tetrahedral and axial octahedral bonds dramatically increased the Curie temperature (Tc) from 43 K (Mn 3 O 4) to 62 K (Co 0.5 Mn 2.5 O 4). • The ferrimagnetic ordering and the exchange interactions were verified through the Lotgering-Srinivasan- Seehra model in Co 0.5 Mn 2.5 O 4. • The observed cluster glass behaviour in Co 0.3 Mn 2.7 O 4 is apparently due to strongly interacting magnetic clusters formed as the result of geometric frustration and short-range antiferromagnetic interactions. • In Co 0.1 Mn 2.9 O 4 , incomplete establishment of glassy states is presumed and, in the case of Co 0.5 Mn 2.5 O 4 , cluster glass state is completely vanished. • The co-existence of long- range ferrimagnetic ordering and cluster glass state in Co 0.3 Mn 2.7 O 4 gave rise to an exchange bias effect. [ABSTRACT FROM AUTHOR]

Iridium-based double perovskite oxides (DPO) provide a rich variety of multifunctional properties and technological applications due to their entangled spin-orbit coupling (SOC) state. Here, we theoretically investigated the electronic and magnetic properties of newly discovered Lu 2 NiIrO 6 DPO, in which both the electron correlation and the SOC play vital roles. Our results revealed that a strong antiferromagnetic superexchange interaction between Ni and Ir ions results in a ferrimagnetic ordering. Interestingly, the computed Curi temperature of 225 K is very close to the experimentally observed value of 207 K [Inorg. Chem. 58 , 397 (2019)]. Moreover, the system exhibits a Mott-insulating (energy gap mainly exists between 5 d -orbitals of Ir ion) behavior with an energy gap of 0.20/0.26 eV with/without SOC. The calculated total magnetic moments are 0.95 and 1.04 μ B /f.u. with and without SOC, respectively, which mainly arises from Ni ion and inclusion of SOC induced a substantial orbital moment of − 0.45 μ B /Ir. A combination of low/high energy band gap in the spin-majority/minority channel and substantial spin(orbital) moment makes the system an appealing candidate for spintronic applications. • Antiferromagnetic superexchange coupling leads the system to Ferrimagnetic ground state. • System exhibits a Mottinsulating behavior with an energy gap of 0.26 eV. • SpinOrbit coupling induced a substantial orbital moments on Ir atom. • System show a high Curie Temperature of 225 due to substantial octahedral distortion. [ABSTRACT FROM AUTHOR]