Magnetocrystalline Anisotropy Constant Research Articles

Magnetic Behaviour, and initial permeability of green synthesized Co2+ substituted Ni-Zn ferrite

This study investigates the magnetic properties of Ni0.55−xZn0.45CoxFe2O4 (x = 0.0, 0.15, 0.25, 0.35, 0.45, 0.55) ferrite nanoparticles synthesized via the green synthesis route using orange juice as a green reductant. The magnetocrystalline anisotropy constant (Ms) and the Bohr magneton number (nB) of the Ni-Zn ferrites increase linearly with an increase in the content of Co2+ ions. The magnetic properties such as Saturation magnetization, Coercive force, and remanence ratio (Mr / Ms) are determined. The Curie temperature for the studied ferrites is found to be reduced upon doping with cobalt ions and is considered as the weakening of the A-B exchange interaction.

Nano-structuring of all-d-metal NiCoMnTi-based Heusler compounds

The emerging all-d-metal Ni(Co)MnTi-based Heusler compounds attract extensive attention because it can potentially be employed for solid-state refrigeration. However, in comparison to the abundant physical functionalities in bulk conditions, the hidden properties related to the NiCoMnTi-based Heusler nanoparticles (NPs) have not yet been investigated experimentally. Here, we present NiCoMnTi Heusler NPs that have been manufactured by spark ablation under Ar gas flow, and the related magnetic and microstructural properties have been studied. Compared with the bulk sample, it is found that the magneto-structurally coupled transition in the bulk sample has collapsed into a magnetic transition for the NPs sample. Superparamagnetic NPs with widely distributed dislocations have directly been observed by high-resolution transmission electron microscopy. For the NPs, the magnetocrystalline anisotropy constant is 3.54 × 104 J/m3, while the saturation magnetization after post-treatment has been estimated to be around 26 Am2 kg−1. Our current research reveals that Ni-Co-Mn-Ti-based quaternary NPs could show interesting properties for future nano-application, and the produced NPs will further expand the functionalities of this material family.

Single phase metamaterial behavior in [formula omitted] and [formula omitted] doped cobalt ferrites

This paper reports the characteristic properties of CoFe2O4(CFO), Co0.98Ag0.02Fe2O4(CAFO), and Co0.98Ti0.02Fe2O4(CTFO) spinel ferrites of Fd3‾m space group and grain size in the range of 160 – 170 nm. Fourier transform infrared spectra of these samples have revealed the metal-oxygen bands in the range of 448– 542 cm−1. Raman spectra have shown six distinct peaks corresponding to the mixed spinel structure, which have been used to calculate the cation distribution of the samples. The magnetic measurement at room temperature shows that after the doping of Ti4+ ions, the saturation magnetization increases from 47.70 to 66.68 emu/g, and coercivity decreases from 1.84 to 1.61 kOe, making the sample magnetically softer. The law of approach to saturation magnetization has been used to estimate the value of magneto crystalline anisotropy constant. The dielectric behavior of the samples has been thoroughly studied in this paper. The dielectric constant is positive below 300 °C; its value is comparable for CFO and CAFO samples but higher for CTFO. Above this temperature, the samples show an uncommon behavior of negative dielectric constant corresponding to the single phase metamaterial state and its value increases as temperature rises. This behavior can be interpreted with the help of Drude model of plasmonic resonance. The Nyquist plots change their properties from RC to RL type in this region. Such single phase metamaterials with negative dielectric constant could be useful for high temperature microwave applications.

Synthesis and characterization of NiFe2 O4 nanoparticles by tartaric acid assisted sol-gel auto-combustion method

Nickel ferrite nanoparticles were synthesized by modified sol-gel auto-combustion method. The final product obtained was annealed at 600 °C. The thermal, structural, morphological, vibrational, optical and magnetic properties were studied using TGA, XRD, SEM, FTIR, UV-DRS and VSM techniques, respectively. The thermo gravimetric analysis shows three step decomposition of residual nitrate and tartrate complexes with a total weight loss of 6.69% below 600 °C. Further, there was no significant weight loss above 600 °C. XRD confirmed the spinel cubic phase with Fd3m space group. The average crystallite size was 14 nm. An agglomerated random morphology with porous flake like microstructure was observed. The vibrational analysis confirmed the presence of Ni-O, Fe-O stretching vibrational modes in the wave number range 400-600 cm−1. Tetrahedral site (kTd) and octahedral site (kOh) force constant values were 2.20×105 and 1.31×105 dynes/cm, respectively. From UV-DRS spectra, the Kubelka-Munk function was used to calculate the optical band gap and it was 1.71 eV. The magnetic saturation, retentivity and coercive field values: Ms = 22.35 emu/gm, Mr = 5.20 emu/gm, Hc = 165 Gauss were obtained from VSM analysis. The calculated magnetic moment value was 1.115 μB. The law of approach to saturation was employed to analyze the VSM data in saturation region. The calculated magneto-crystalline anisotropy constant, K1 value was 0.857×105 erg/cc.

Effects of Ti doping on the magnetic and microstructure properties of the lower magnetic anisotropy CoCrPtRu-oxides layer in a perpendicular recording media

Areal density capacity is constrained by linear and track density, and the recent advancements in magnetic layer structures have led to the development of segmented media. This configuration incorporates a graded magnetic anisotropy layer introduced through a non-magnetic exchange control layer. Optimizing this structural design yielded improvements in the signal-to-noise ratio (SNR) and an elevation in areal density capacity. To comprehensively investigate the magnetic properties and microstructure of the lower magnetocrystalline anisotropy constant (Ku) CoCrPtRu-oxides magnetic capping layer individually, we deposited the (0002) textured magnetic capping layer CoCrPtRu-oxides on (0002) Ru/NiW/NiTa underlayers. Additionally, metallic Ti was introduced into CoCrPtRu targets, replacing half of Ru, resulting in the deposition of the (0002) textured CoCrPtRuTi-oxides film was also deposited and compared to CoCrPtRu-oxides film. A comparative analysis was conducted between the CoCrPtRu-oxides and CoCrPtRuTi-oxides films. Microstructural image mapping and chemical composition analysis revealed that the introduced Ti in core grains diffused to the grain boundaries, enhancing grain separation. This diffusion was facilitated by the more negative formation energy of TiO2 (-3.512 eV/atom) compared with other oxides in the film. Consequently, the CoCrPtRuTi-oxides film exhibited slightly larger grain boundary areas (52%) and smaller grain sizes. Moreover, perpendicular coercivity (243.50 kA/m) and anisotropy were higher. This insight suggests a potential strategy for improving segregation by doping metallic elements, such as Ti, into the core grains, emphasizing the importance of not merely increasing the oxide content (e.g., TiO2).

Tuning magnetocrystalline anisotropy by Au ion induced defects in NiO thin films

Intercalations and doping effectively induce room-temperature ferromagnetism in antiferromagnetic NiO thin films. This report investigates the defect-controlled ferromagnetic properties of Au ion implanted highly crystalline NiO thin films at different ion fluences. Low energy heavy ion irradiation leads to preferential sputtering of Ni and O atoms that create various kinds of vacancies and interstitial defect states within the matrix. These defect states are responsible for bandgap narrowing and changing the crystallite size and show the defect luminescence in the NiO thin films. It has been observed that the intrinsic Ni and O defects with the non-stoichiometric ratio of these atoms during crystal growth, resulting in uncompensated spins, induce the ferromagnetic properties in the pristine sample and are further modulated with ion fluences. The presence of defects gives rise to energy variations due to the modification of the magnetic environment of Ni ions in the lattice and tune the blocking temperature and magnetocrystalline anisotropy. The magnetocrystalline anisotropy constant (K) reaches its maximum at 70 erg/cm3 with ion fluence and decreases at the highest fluence because of the suppression of exchange interaction by a large number of defect centers. The modulation of anisotropy in NiO thin films is intricately linked to crystallite size, bandgap narrowing, blocking temperature, and the magnetization mechanism, which is a direct result of defect concentrations in the material.

A comprehensive study on MnZn ferrite materials with high saturation magnetic induction intensity and high permeability for magnetic field energy harvesting

Manganese-zinc (MnZn) ferrites have important applications in energy conversion, transmission, and harvesting. MnZn ferrite for magnetic field energy harvesting is expected to enhance the saturation magnetic induction (Bs), initial permeability (μi), and Curie temperature (Tc) aspects simultaneously, which is beneficial to the energy harvesting efficiency and safety of the device. In this paper, various formulations of MnZn ferrite samples were prepared by the conventional oxide ceramic process. The cation distribution was determined through Rietveld refinement of XRD patterns Based on this, the M–T curves were fitted by combining Néel molecular field theory with Brillouin functions. The greatest influence on the Curie temperature was found to be the molecular field coefficient between the A and B sites. The magnetization mechanism of MnZn ferrite was comprehensively analyzed by fitting the complex permeability spectrum, magnetocrystalline anisotropy constant, and magnetostriction coefficient. The ratio of domain wall displacement magnetization to domain rotation magnetization shows an increasing and then decreasing trend with Fe content, while |K1| shows an opposite trend. Finally, MnZn ferrite materials with excellent overall performance (Bs = 505mT, μi = 9016, Tc = 447 K) were prepared by investigating the magnetization mechanism.

Temperature dependent magnetic and electrical transport properties of lanthanum and samarium substituted nanocrystalline nickel ferrite and their hyperthermia applications

Structural, optical, temperature dependent magnetic and electrical properties have been investigated for the nanocrystalline NiFe1.97RE0.03O4 (RE = La3+ and Sm3+) compound. Without any signs of a secondary REFeO3 phase, the Rietveld refinement reveals a single-phase spinel structure possessing cubic symmetry for current samples. The decrease in lattice constant has been observed as a result of RE ions substitution. The TEM micrographs reveal nanosized particles with an average size of 35 ± 3 nm and 32 ± 3 nm for La3+ and Sm3+ substituted samples. EDX spectra of both samples show good compositional homogeneity. HRTEM micrographs of both samples show well resolved lattice fringes and their inter-planar spacing matches with that obtained from the Rietveld analysis of the XRD patterns. The concentration of Fe2+ and Fe3+ ions has been estimated from the XPS spectra analysis and it is found to be ∼ 22% and 78% for NiFe1.97La0.03O4 and, 20% and 80% for NiFe1.97Sm0.03O4 compound. The optical energy band gap for rare earth substituted samples is found to be more than that of pure nickel ferrite. The value of saturation magnetization (Ms) and magneto-crystalline anisotropy constant (K1) estimated from the “Law of Approach to Saturation” equation for rare earth substituted samples are found to be less than that of pure nickel ferrite. However, an enhanced value of coercivity has been observed with RE substitution. ZFC (zero field cooling) and FC (field cooling) DC magnetization curves measured at 100 Oe in the temperature range of 60–400 K reveal a combination of weak and intermediate forms of magnetic interaction between the particles for both samples. Temperature dependent analysis of saturation magnetization and coercivity employing modified Bloch’s law and Kneller’s relation supports the nanomagnetic behavior of both samples. Under an AC magnetic field of 14.92 kA/m and frequency 337 kHz, the SAR and ILP values have been found to be ∼ 331 W/g and 4.22 nHm2/kg for NiFe1.97La0.03O4 and, ∼ 241 W/g and 3.21 nHm2/kg for NiFe1.97Sm0.03O4. The dielectric relaxation data have been analyzed at various temperatures ranging from 40 to 300 0C over the frequency range 100 Hz-1 MHz using electrical impedance spectroscopy. The dielectric constant for rare earth substituted samples is found to be more and their AC conductivity is observed to be less than that of pure nickel ferrite. The analysis of temperature dependent AC conductivity employing Jonscher’s power law suggests that the charge carrier’s conduction mechanism of both samples follows the small polaron hopping mechanism below 200 0C, thereafter; it follows the correlated barrier hopping mechanism. The activation energy estimated by imaginary impedance spectra is found to be 0.411 eV and 0.398 eV for NiFe1.97La0.03O4 and NiFe1.97Sm0.03O4 which is more than that of pure nickel ferrite. The Cole-Cole plots at different temperatures suggest the presence of non-Debye-type relaxation. The modeling of Cole-Cole plots with equivalent circuits for both samples confirms the contribution of both grain and grain boundary in electrical conduction. The estimated stretching exponential factor by fitting the modified KWW (Kohlrausch-Williams-Watts) equation to the imaginary modulus curve reveals relatively more dipole-dipole interaction in NiFe1.97Sm0.03O4 than that of the La3+ substituted sample.

The regulation of high-frequency magnetic properties of NiZnCo ferrite for miniaturized antenna application

Demand for communication devices with miniaturization and high-frequency capability requires materials with high permeability, matching permittivity, low loss, and high operating frequency. In this study, the micromorphology of NiZnCo ferrites synthesized by the co-precipitation method is regulated by changing the sintering temperature, obtaining a domain structure with a high-performance factor (PF). Specifically, the effect of Co ion content on the static and high-frequency magnetic properties of NiZnCo ferrites is analyzed at a sintering temperature of 800 °C. Results reveal that the value of Snoek limit and the magnetocrystalline anisotropy constant of NiZnCo ferrites increase with Co ion content enhances from 0.2 to 0.5, thereby PF elevates from 34.7 GHz (at the maximum operating frequency f0 = 1.04 GHz) to 48.7 GHz (f0 = 2.25 GHz). PF value of Ni0.31Zn0.19Co0.5Fe1.98O4-δ ferrite is measured to be 48.7 GHz at 2.25 GHz. Furthermore, a planar inverted F antenna (PIFA) is designed using Ni0.31Zn0.19Co0.5Fe1.98O4-δ ferrite. The PIFA exhibits a maximum gain of 3.7 dB and a miniaturization rate of 4.6 %. This study holds significant implications for the development of magneto-dielectric materials for use at 2.0 GHz.

Giant coercivity induced by perpendicular anisotropy in Mn2.42Fe0.58Sn single crystals

We report the discovery of a giant out-of-plane coercivity in the Fe-doped Mn3Sn single crystals. The compound of Mn2.42Fe0.58Sn exhibits a series of magnetic transitions accompanying with large magnetic anisotropy and electric transport properties. Compared with the ab-plane easy axis in Mn3Sn, it switches to the c-axis in Mn2.42Fe0.58Sn, producing a sufficiently large uniaxial anisotropy. At 2 K, a giant out-of-plane coercivity (Hc) up to 3 T was observed, which originates from the large uniaxial magnetocrystalline anisotropy. The modified Sucksmith-Thompson method was used to determine the values of the second-order and the fourth-order magnetocrystalline anisotropy constants K1 and K2, resulting in values of 6.0 × 104 J/m3 and 4.1 × 105 J/m3 at 2 K, respectively. Even though the Curie temperature (TC) of 200 K for Mn2.42Fe0.58Sn is not high enough for direct application, our research presents a valuable case study of a typical uniaxial anisotropy material.

Magnetocrystalline anisotropy of interstitially and substitutionally Sn-doped MnBi for high temperature permanent magnet applications

First-principles calculations were performed to calculate the electronic structures of low temperature phase (LTP) MnBi (Mn50Bi50) and substitutionally and interstitially Sn-doped MnBi [Mn50Bi25Sn25, (Mn0.5Bi0.5)66.7Sn33.3]. Brillouin function predicts the temperature dependence of saturation magnetization M(T). Sn substitution for Bi in MnBi (Mn50Bi25Sn25) changes the magnetocrystalline anisotropy constant (Ku) from −0.202 MJ/m3 (the in-plane magnetization) for LTP MnBi to 1.711 MJ/m3 (the out-of-plane magnetization). In comparison, the Ku remains negative but slightly decreases to −0.043 MJ/m3 when Sn is interstitially doped in MnBi [(Mn0.5Bi0.5)66.7Sn33.3]. The Curie temperature (TC) decreases from 716 K for LTP Mn50Bi50 to 445 K for Mn50Bi25Sn25 and 285 K for (Mn0.5Bi0.5)66.7Sn33.3. Mn50Bi25Sn25 has a lower magnetic moment of 5.034 μB/f.u. but a higher saturation magnetization of 64.2 emu/g than (Mn0.5Bi0.5)66.7Sn33.3 with a magnetic moment of 6.609 μB/f.u. and a saturation magnetization of 48.2 emu/g because the weight and volume of the substitutionally Sn-doped MnBi are smaller than the interstitially Sn-doped MnBi. The low Curie temperature and magnetization for Sn-doped MnBi are attributed to the high concentration of Sn. Thus, future study needs to focus on low Sn-concentrated MnBi.

High magneto-mechanical hysteresis-type damping in FeGaMo alloys

Optimization of the damping capacity of conventional FeCr-based ferromagnetic high damping alloys (HDAs) usually involves a trade-off in terms of degradation of mechanical properties due to grain coarsening caused by high-temperature annealing. In this work, new ferromagnetic HDAs of FeGaMo alloys with different Mo contents are reported, which can exhibit high damping when treated in a medium temperature range. Among these alloys, the alloy with Mo content of 2 at% exhibits the best damping capacity of 4.20 × 10−2 (Q−1, equivalent to a special damping capacity SDC of 0.26). It is found that the Mo element has a high solid solubility in the FeGa alloy, and when the Mo content is 2 at%, only isolated tiny precipitations are observed in the matrix. These small precipitates have a negligible effect on hindering domain motion, and the corresponding coercivity change is extremely weak compared to the Mo-free FeGa alloy. As the Mo content increases to 4 at% or 6 at%, Mo-rich phases precipitate within the grains and along the grain boundaries, resulting in an increasing coercivity. Interestingly, as the Mo content increases, the domain density in the (001) and (110) surfaces gradually increases and the arrangement of magnetic domains becomes more tortuous due to the decrease in the magnetocrystalline anisotropy constant. For the FeGaMo alloy with 2 at% Mo content, the high damping capacity mainly arises from the energy loss caused by the high density of irreversible motion of domain walls (DWs) under the applied stress, and as the Mo content continues to increase, the significant precipitation of Mo-rich phases severely restricts the movement distance of DWs, leading to a decrease in damping. This work provides valuable insights for the design and research of new ferromagnetic high damping materials in the future.

Role of Cu-substitution on microstructural, magnetic, magnetostrictive and dielectric properties of sintered NiFe2O4

This study examines the impact of Cu-amalgamation on the microstructural, magnetic, magnetostrictive, and dielectric properties of sintered nickel ferrite (NiFe2O4) ceramics. Without post synthesis calcination, the series of Ni1-xCuxFe2O4 (0 ≤ x ≤ 1) samples were synthesized via an autocombustion process with glycine (1 Mole/mole of metal ion) as a fuel. XRD analysis of the as-synthesized samples revealed that compositions up to x = 0.75 were phase pure. However, impurity CuFeO2 was detected in the x = 1 (CuFe2O4) sample, leading to its exclusion from further processing and testing. After sintering the compacted pellets (12 mm diameter and 3 mm thickness) at 1200 °C for 2 h, compositions up to x = 0.5 were confirmed as phase pure, prompting further characterization of these samples' structural, microstructural, magnetic, and dielectric properties. The unit cell dimension increased from 8.3268 Å for NiFe2O4 (x = 0) to 8.3560 Å for Ni0.5Cu0.5Fe2O4 (x = 0.50) due to the substitution of larger-sized ion (Cu2+) for the smaller-sized ion (Ni2+) in NiFe2O4. Notably, the addition of Cu facilitated substantial grain growth, as observed in the SEM micrographs, where the grain size increased from 556 nm for x = 0 to 13 μm for x = 0.5. As the Cu-content increased in Ni1-xCuxFe2O4, magnetic parameters such as TC (Curie temperature), K1 (Magnetocrystalline anisotropy constant), HC (Coercivity), and MS (Saturation magnetization) decreased. This decrease can be attributed to the replacement of the high-magnetic cation (Ni2+, 2 μB) with the low-magnetic cation (Cu2+, 1 μB) in the octahedral coordination site of NiFe2O4. The x = 0 and 0.5 samples exhibited a maximum magnetostriction strain (λmax) of ∽-35 ppm, and for x = 0.25 sample the value is −24 ppm. In terms of dielectric properties, the permittivity count of the x = 0 sample was higher than that of x = 0.25 and 0.5 samples in the lower frequency regime, likely due to a larger surface area (smaller grain size) contributing to significant surface polarization. Conversely, in the higher frequency regime, the samples with x = 0.25 and 0.5 demonstrated higher permittivity than the parent sample. The changes in dielectric behavior in the Cu-substituted samples were explained based on the microstructure of the samples.

Tuning of magnetic properties of Al-doped cobalt ferrite nanofiber prepared by electrospinning technique

The Al-doped cobalt ferrite (CoFe2-xAlxO4) nanofiber has been prepared by employing the electrospinning technique. All the nanofibers are characterized by the XRD technique. The Rietveld refinement of the XRD pattern reveals the spinel cubic structure with the Fd m space group. The TEM micrographs confirm the formation of nanofiber with a nearly uniform diameter of ∼137 ± 10 nm. The magnetic properties of all the nanofibers have been investigated by measuring the M-H hysteresis loops with the help of a Vibrating sample magnetometer (VSM). The M-H loops analysis demonstrates a reduction in the saturation magnetization, and coercivity from 106.88 emu g−1 to 40.01 emu g−1 and 0.897 kOe to 0.324 kOe, respectively, with the increase in Al concentration in the nanofibers. The ‘Law of Approach to Saturation’ technique has been employed to understand the magnetocrystalline anisotropy constant in the samples. The magnetocrystalline anisotropy constant (K 1) decreases with the increase in Al3+ substitution in place of Fe3+ in the spinel cobalt ferrite nanofibers. A squeezing effect on the M-H loop near M = 0 is observed and, it has been analyzed by a hysteresis loop width (∆H) versus magnetization (M) plot. The squeezing effect has been observed due to the exchange interaction phenomenon between the magnetic and non-magnetic atoms in the Al-doped cobalt ferrite nanofiber. The magnetic properties study demonstrates that Al-doped cobalt ferrite nanofiber exhibits soft magnetic nature.

Large ordered moment with strong easy-plane anisotropy and vortex-domain pattern in the kagome ferromagnet Fe3Sn

We report the magnetic anisotropy of kagome bilayer ferromagnet Fe3Sn probed by the bulk magnetometry and magnetic force microscopy (MFM) on high-quality single crystals. The dependence of magnetization on the orientation of the external magnetic field reveals strong easy-plane magnetocrystalline anisotropy and anisotropy of the saturation magnetization. The leading magnetocrystalline anisotropy constant shows a monotonous increase from K1≈−1.0×106 J/m3 at 300 K to −1.3×106 J/m3 at 2 K. Our ab initio electronic structure calculations yield the value of total magnetic moment of 7.1 μB/f.u. and a magnetocrystalline anisotropy energy density of −0.57 meV/f.u. (−1.62×106J/m3) both being in reasonable agreement with the experimental values. The MFM imaging reveals micrometer-scale magnetic vortices with weakly pinned cores that vanish at the saturation field of ∼3 T applied perpendicular to the kagome plane. The observed vortex-domain structure is well reproduced by the micromagnetic simulations, using the experimentally determined value of the anisotropy and exchange stiffness.

Magnetic properties of chains of spherical nanoparticles with cubic magnetic anisotropy: A Monte Carlo study

Monte Carlo techniques are used to simulate magnetic properties of chains of identical, spherical, single-domain, ferromagnetic nanoparticles with cubic magnetocrystalline anisotropy. Nanoparticles are placed along a straight line with their positions and directions of anisotropy axes fixed in changing external magnetic field. Hysteresis curves as well as zero field cooled (ZFC) and field cooled (FC) experiments are simulated for chains of different lengths, i.e. differing in both: the number of particles and inter-particle distances. Strongly anisotropic dipole–dipole inter-particle interactions lead to significant differences in system’s response to the external magnetic fields oriented parallel and perpendicular to the chain, and further, to the occurrence of wasp-waisted hysteresis loops. We compare results for chains that differ in the size of particles they are built of. To get the idea about the quantitative scale of the discussed phenomena we assume values of magnetocrystalline anisotropy constants for fcc-Co.

Ultrahigh microwave frequency resonance of Y2Co17 thin film with planar anisotropy

Y2Co17 thin films grown along the c axis with planar anisotropy were fabricated by magnetron sputtering and annealed by vacuum heat treatment with rapid water-cooling technologies. The results demonstrate that the annealing temperature had a significant impact on structures and morphologies of the films. The phase structure transformed from rich fcc-Co phase to Y2Co17 intermetallic compounds with the increasing annealing temperature. The Y2Co17 thin film annealed at 600 °C has a saturation magnetization of around 13.5 kGs and a negative magneto-crystalline anisotropy constant of −1.88 × 106 erg/cm3, respectively. The high-frequency performance of the film show that, in the absence of an induced in-plane anisotropy field, the zero-field natural resonance frequency exceeds 4 GHz.

Temperature annealing dependence of structural, magnetic, and antibacterial properties of silver substituted cobalt ferrite nanoparticles produced by coprecipitation route

In this study, silver-substituted cobalt ferrite (Ag0.02Co0.98Fe2O4) nanoparticles were successfully sensitized by the coprecipitation method. Annealing temperature treatment was used to modify the physical properties, i.e., 200 °C, 300 °C, 400 °C, and 500 °C. XRD analysis showed an increase in the annealing temperature, the crystallite size increased from 19.78 to 24.11 nm, and the grain size increased from 54.75 to 61.39 nm. The FTIR spectrum showed two prominent absorption bands around k ∼577 and k ∼381 cm−1, allowing metal oxide absorption in the tetrahedral and octahedral sites. There is a redistribution of cations which is more significant at the tetrahedral sites than at octahedral sites, toward a perfect spinel structure. An increased annealing temperature increased the saturation magnetization and coercive field from 31.80 to 50.60 emu g−1 and 651 to 1,077 Oe, respectively, attributable to an increase in the magnetocrystalline anisotropy constant. The evaluation of S. aureus and E. coli showed that Ag0.02Co0.98Fe2O4 indicated the zone of inhibition (ZOI) around the disks due to its antibacterial properties. The most significant on S.aureus and E.coli were 12.73 mm (mortality of 88%) and 12.43 mm (mortality of 80%), respectively, for Ag0.02Co0.98Fe2O4 annealed at 200 °C that have the minor grain size materials.

Spin-lattice interaction parameters from first principles: Theory and implementation

A scheme is presented to calculate on a first-principles level the spin-lattice coupling (SLC) parameters needed to perform combined molecular-spin dynamics (MSD) simulations. By treating changes to the spin configuration and atomic positions on the same level, closed expressions for the atomic SLC parameters could be derived in a coherent way up to any order. The properties of the SLC parameters are discussed considering separately the symmetric and antisymmetric parts of the SLC tensor. The changes due to atomic displacements of the spin-spin exchange coupling (SSC) parameters estimated using the SLC parameters are compared with the SSC parameters calculated for an embedded cluster with the central atom displaced, demonstrating good agreement of these results. Moreover, this allows to study the impact of different SLC contributions, linear and quadratic with respect to displacements, on the properties of the modified SSC parameters. In addition, we represent an approach to calculate the site-diagonal SLC parameters characterizing local magnetic anisotropy induced by a lattice distortion, which is a counterpart of the approach based on magnetic torque used for the investigations of magneto-crystalline anisotropy (MCA) as well as for calculations of the MCA constants. In particular, the dependence of the induced magnetic torque on different types of atomic displacements is analyzed.

Magnetic properties, critical behaviors and magnetocaloric effect in non-stoichiometric spinel type Co1+xCrxFe2-xO4

The magnetic properties, magnetocaloric effect, and critical analysis of magnetic behavior of Co1+xCrxFe2-xO4 (x = 0.125, 0.250, 0.375, and 0.500) with a non-stoichiometric ratio are studied in detail. All the synthesized samples exhibit single-domain behavior. The Cr3+ associated with excess Co2+ led to tuning the magnetic moment, exchange interaction, magnetocrystalline anisotropy constant, and microwave frequency. The second-order magnetic phase transition has been confirmed from the Arrot and Arrot-Noakes plots for all the samples. The Cr3+ associated with excess Co2+ also tuned the magnetocaloric (MCE) properties showing the maximum relative cooling power of 156 J kg-1, which is a higher value than that of previously reported Cr3+ substituted stoichiometric cobalt ferrite. The reliability of MCE and the nature of the magnetic phase transition of the investigated samples are confirmed by analyzing the critical exponent analysis, universal curve scaling, and scaling analysis of MCE.