Decrease In Saturation Magnetization Research Articles

Impact of Cr Substitution on Structural, Magnetic, Electric and Impedance Study of Mn-Ni-Zn Ferrites

A series of Cr3+-substituted Mn-Ni–Zn ferrites; Mn0.5Ni0.1Zn0.4Fe2-xCrxO4 (x = 0.0 - 0.4 in a step of 0.1) were prepared by traditional solid-state reaction route. The structural, magnetic, dielectric properties and impedance spectroscopy of these compositions were studied. Phase identification and lattice constant (a0) determination were carried out by X-ray diffraction (XRD). The XRD patterns established the fabrication of a single-phase spinel structure. The FESEM micrographs exposed that the average grain size () increased slightly with chromium (Cr) substitution and then decreased for a higher concentration of chromium in the composition. The real part of initial permeability () diminished owing to the enhanced porosity of the compositions with the increase of Cr3+ content in the composition. The highest relative quality factor (RQF) was attained for the samples with x = 0.1. The magnetic hysteresis was investigated to know the effect of Cr3+ substitution in the composition of the magnetic properties. The decrease of saturation magnetization (Ms) with an enhancement in Cr3+ might be triggered by switching of Fe3+ ions from octahedral to tetrahedral site. The samples with x = 0.1 exhibited the highest anisotropy constant (K). Curie temperatures of the investigated samples were significantly modified to lower temperatures with the Cr3+ content. The frequency characteristics of dielectric properties and impedance spectroscopy had been investigated. The highest dielectric constant (ε') and resistivity were observed for x = 0.1 and x = 0.2 samples. The complex impedance spectra analysis reveals in-depth information about the conduction mechanism, microstructure, and orientation of the grains in the samples.

Influence of annealing temperature on degradation efficiency and iron oxide transformations in CeO2/Fe-oxide sorbents

The microstructural and physical properties of magnetically separable CeO2 (5 wt.%)/Fe-oxide sorbents, applicable for the decomposition of organophosphorus pesticides, are analyzed in dependence on calcination temperature. The sorbents are prepared using a two-step procedure: (1) synthesis of magnetite core from cheap and commercially available raw materials; and (2) the formation of cerium (III) carbonate by precipitation with the ammonium hydrogen carbonate, containing re-dispersed magnetite. The cerous carbonate/magnetite precursor is annealed in a muffle furnace at temperatures ranging from 473 to 1073 K for 2 h to obtain the CeO2/Fe-oxide reactive sorbents. Structural characterization of the samples is performed using X-ray diffraction, scanning electron microscopy, Raman and Fourier transform infrared spectroscopy. Magnetic properties are obtained from hysteresis loops, field-cooled and zero-field-cooled curves, first-order reversal curve (FORC) diagrams, and Henkel plots. Sorbents exhibit an increase in coercivity from 0.2 kA/m to about 20 kA/m and a decrease in saturation magnetization from roughly 50 Am2/kg to 1 Am2/kg after annealing at 973 K. This deterioration of magnetic properties is caused by the transformation of magnetite and maghemite into weakly ferromagnetic hematite, with a typical peak in FORC diagram and a Morin transition at about 200 K. The degradation efficiency towards parathion and paraoxon methyl is about 30% for samples annealed from 473 K to 773 K.

Microstructure, magnetic properties of Ho3+ substituted Ni-Cu-Zn spinel ferrites and application for one pot synthesis of dihydropyrimidinones

Nanoparticles of Ni-Cu-Zn spinel ferrites with Ho3+ substitution were synthesized through the sol–gel auto combustion route. It is illustrated from thermogravimetric analysisand differential thermal analysiscurve that the decomposition of precursors takes place in the temperature range 350–460 oC. The Energy dispersive spectroscopy confirmed the mixing of the Fe, Ni, Cu, Zn, Ho and oxygen elements in stoichiometry proportion in pure and substituted spinel ferrites with desired stoichiometry. X-ray diffraction pattern confirmed the formation of cubic spinel structure without any impurity phases. Lattice constant, X-ray density increases while average crystallite size decreases with increased Ho3+substitution in Ni-Cu-Zn ferrites. The two strong IR absorption bands observed in the range 565–568 (ν1) and 409–438 (v2) cm−1. The obtained crystallite size lies between of 18 – 26 nm, confirmed from transmission electron microscopy. The microstructures of the calcinated spinel ferrites were evaluated by SEM and TEM. It is observed that the increase in concentration of Ho3+ ions saturation magnetization decreases. Prepared Ho3+ substituted Ni-Cu-Zn spinel ferrites were used as catalyst to synthesize the 3,4-dihydropyrimidin-2(1H)-ones.[copyright information to be updated in production process]

Effects of Scandium Doping on Structural and Magnetic Properties of Cobalt Ferrite Thin Films

Structural and magnetic properties of Sc-substituted cobalt ferrites were studied by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and vibrating-sample magnetometry. The ScSUBx/SUBCoFeSUB2-x/SUBO₄ (x ≤ 0.3) specimens prepared as thin films by a sol-gel deposition method were polycrystalline having cubic spinel structure with a small increase in the lattice constant compared to CoFe₂O₄. The Raman spectral analyses suggested that the Sc-doped specimens have higher tetrahedral CoSUP2+/SUP population than that of pristine CoFe₂O₄. The magnetic hysteresis curves of the ScSUBx/SUBCoFeSUB2-x/SUBO₄ specimens indicated that the saturation and remanent magnetization decrease proportionally with the increase of Sc composition (x). The decrease in the ferrimagnetic parameters is understandable in terms of the octahedral substitution of non-magnetic ScSUP3+/SUP ions. However, the octahedral ScSUP3+/SUP ions caused an increase of the coercivity.

Impact of nickel substitution on structure, magneto-optical, electrical and acoustical properties of cobalt ferrite nanoparticles

In this study, we have investigated the impact of nickel substituted cobalt ferrite nanocrystals, which were synthesized by a facile co-precipitation technique. The various physical properties such as structural, electrical, magneto-optical and thermal were studied. These properties were characterized using XRD (X-ray diffraction), FT-IR (Fourier-transform infrared spectroscopy), VSM (vibrating sample magnetometer), UV-visible (Ultraviolet–visible) spectra, LCR (Inductance capacitance resistance) meter and photoacoustic spectrophotometer, respectively. From XRD analysis, single face cubic structure (Fd3m) was determined. It was found that as the nickel substitution increased, the crystallite size (D) was decreased from 17.4 ± 1.7 nm to 6.7 ± 1.2 nm. Various structural parameters such as oxygen positional parameters, bond length and cation distribution were determined. Using FT-IR technique, various types of interionic bonds and the elastic properties with their distribution of ions in the formation of spinel phase was found between 400 and 600 cm−1 for the as-synthesized nanocrystals. The aspect of morphology was determined using TEM (transmission electron microscopy). Surface analysis for the as-synthesized products was found to increase from about 41.8 ± 0.6 m2/g to around 92.7 ± 2.1 m2/g with the increase in concentration of Ni ions. From UV-visible spectrum, empirical relation was calculated which indicates the nature of nano crystallinity of the as-synthesized sample. The electrical properties of the as-synthesized samples were premeditated by utilizing LCR meter; at a function of frequencies (10 Hz −10 MHz) at room temperature (RT) impedance was analyzed. Impedance study confirmed that the as-synthesized sample with major grain boundary contributes to conduction. The product with x = 0.9 shows a low dielectric loss and high dielectric constant and henceforth it can used in electromagnetic devices with high frequency. The hysteresis loop elucidates a steadily decrease in Bohr magneton and saturation magnetization, which indeed exhibited a non-linear conduct, where else we could observe a significant increase of anisotropy constant. The thermal properties such as diffusivity, conductivity and effusivity were determined using photoacoustic spectrophotometer and it was found that highly substituted nano-sample has high thermal stability when compared to the other concentrations.

Structural, Microstructural, Electrical, and Magnetic Properties of CuFe2-(x+y)EuxScyO4 (where x and y vary from 0 to 0.03) Nanoparticles

In the present work, the CuFe2-(x+y)EuxScyO4 nanoparticles were prepared by solution combustion method for reporting the structural, microstructural, dielectric, and magnetic properties of prepared samples. The XRD (X-ray diffractometer) patterns confirm the spinel cubic structure with space group Fd3m. The average crystallite size was found in the range from 25 to 10 nm for x = y = 0.00, 0.01, 0.02, and 0.03 concentrations. The SEM (scanning electron microscopy) investigations indicate the porous nature and particle agglomeration. The elemental composition of the samples was studied by using energy-dispersive X-ray spectroscopy (EDS). The FTIR (Fourier transform-infrared spectroscopy) investigation shows the two absorption bands around 554.07 cm−1 and 468.98 cm−1 due to stretching vibrations of the Cu⟺O metal-oxygen bond at the A-site and stretching vibrations of Fe⟺O metal-oxygen bond at the B-site, respectively. The real and imaginary parts of dielectric constant, dielectric loss tangent, AC conductivity, and impedance spectroscopy have been recorded by the methods of impedance analyzer from the range 0.1 KHz to 1 MHz. The dielectric constant and dielectric loss show maximum value at smaller frequency region and are decreases with increase in frequency. AC conductivity increases with the increase of frequency. The real and imaginary part of impedance spectra as function of frequency was studied. The Cole-Cole plots drawn from the impedance spectra show one semicircle for each of the samples. The magnetic hysteresis loop reveals the soft ferromagnetic nature. The magnetic parameters such as saturation magnetization, coercivity, and remanence magnetization decrease with the increase of Eu3+ and Sc3+ concentration.

EVOLUTION OF FERRO ELECTRIC AND FERRO MAGNETIC PROPERTIES OF RARE EARTH ALUMINIUM SUBSTITUTED M-TYPE BARIUM HEXA FERRITES AT ROOM TEMPERATURE

The ferro-electric and ferro-magnetic properties of rare earth aluminium substituted Mtype barium hexa-ferrites with the composition of BaAlxFe(12-x)O19 where (x=0.2, 0.4, 0.6, 0.8, 1.0 and 1.2) have been prepared by oxides as precursors employing powder metallurgy route. The structural properties, functional groups, 3-D visualization, elemental analysis, surface morphology, magnetic, optical properties and ferro electric properties of the prepared samples have been characterized through X-Ray Diffractometer (XRD), Fourier Transform Infrared Spectroscopy (FTIR), diamond visualization software, Energy Dispersive Spectroscopy (EDS), Scanning Electron Microscopy (SEM), Vibrating Sample Magnetometer (VSM), UV-Visible spectroscopy (UV-VIS) and ZT-IA measurement system respectively. The structural measurements depict the confirmation of M-type barium hexa-ferrite structure. EDS spectrum illustrate the elemental composition of the prepared materials for every corresponding ‘x’ values. The surface morphology shows the existence of platelet like intergranular pores. Magnetic measurements shows that the saturation magnetization (Ms) decreases and coercivity (Hc) increases with increasing aluminium contents. The optical band gap energy increases as the crystallite size decreases. The variation of electric polarization has also been occurred due to the shifting of iron ions in the unit cell structure of oxygen octahedron FeO6.

Effect of chromium ions on the structural, magnetic, and optical properties of manganese–zinc ferrite nanoparticles

The present work describes the synthesis of Mn0.5Zn0.5CrxFe2−xO4 (x = 0.1, 0.2, 0.3) ferrite nanoparticles by solution combustion method and their detailed structural, electrical, magnetic, and optical characterizations. X-ray pattern represents the creation of a single spinel structure. In addition to this, the distribution of cations is also approximated from X-ray study which is then authenticated by the magnetization technique also. The crystalline size (23–21 nm) and lattice parameter (8.39–8.30 A) are found to shrink with the rise in chromium ions. A decrease in saturation magnetization (0.80–0.64 emu/g) and remanent magnetization (0.05–0.03 emu/g) is found with the rise in chromium ions, while the coercivity is found to increase (83–123 Oe) through the adding of chromium ions. FTIR predicted the two absorption bands (ν1 and ν2) near 600 and 400 cm−1. Dielectric constant and loss tangent were observed to decrease with an increase in frequency, whereas AC conductivity attains a nearly constant value at a lower frequency and observed to increase at higher frequencies with the addition of dopant.

Room-temperature ferromagnetism in Gd and Sn co-doped bismuth ferrite nanoparticles and co-doped BiFeO3/MXene (Ti3C2) nanohybrids for spintronics applications

Room-temperature ferromagnetic materials are required for new flourishing spintronic technology. Synthesis of co-doped (Gd, Sn) BiFeO3 (Bi1-xGdxFe1-ySnyO3, x = 0, 0.1, 0.15, 0.25; y = 0.1) nanoparticles and nanohybrid co-doped BiFeO3/MXene system as well as structural morphological, electronic and ferromagnetic properties are analysed. XRD patterns showed distorted rhombohedral structure of pure BFO which undergoes transition of phase from rhombohedral to orthorhombic structure due to the Gd substitution in BFO. From SEM, clear voids and porous network can be observed and agglomeration of particles can be due to the addition of Gd substitutions to the BFO. The hysteresis behaviour was revealed for different concentrations of magnetically active Gd added in BFO host, increments in the concentration of Gd resulted in enhanced saturation magnetizations for different samples mainly due to the alteration in antiferromagnetic ordering at the particle's surface, phase transition due to the Gd substitution, collapse of space modulated spin, suppression of oxygen vacancies and increase in number of Fe ions. The magnetization of the hybrid system shows a clear hysteresis behaviour but with decreased saturation magnetization which is attributed to the super exchange effect at the BGFSO and Ti3C2 interface. Unlike the other reports on magnetism in 2D materials, the present work presents magnetic effect in MXene hybrid system which opens up new material designs for 2D spintronics.

A study of Ca-doped hexaferrite Sr1−xCaxFe12O19 (x = 0.0, 0.05, 0.1, 0.15, and 0.2) synthesized by sol-gel combustion method

Ca-doped Hexaferrites of composition Sr1−xCaxFe12O19 (x = 0.0, 0.05, 0.1, 0.15, and 0.2) were synthesized by the sol-gel combustion method and sintered at the two temperatures of 900 and 1100 °C. X-ray powder diffraction (XRPD) measurements with Rietveld refinement analysis confirmed the formation of pure M-type hexaferrite phase for all samples, except for the x = 0.1 and 0.15 samples, sintered at 1100 °C, which also contained 2% and 0.7% hematite phase. The images obtained from field emission scanning electron microscope indicated all the prepared hexaferrite samples were composed of agglomerated nanoparticles and plate shape morphology for samples sintered at 1100 °C. FT-IR measurements also confirmed the formation of the hexaferrite structure. Hysteresis loops (M–H) of the samples were measured by a vibration sample magnetometer at room temperature, and the results obtained revealed decreasing saturation magnetization with increasing Ca content. Coercivity for the samples sintered at 900 °C was increased with increasing Ca content, while for the samples sintered at 1100 °C, it decreased due to the particle size effect. The optical band gaps of the prepared samples were in a range suitable for photovoltaic application. Dielectric constant (ε) and dielectric loss (tanδ) were measured for all samples, and the values for ε and tanδ for the samples sintered at 900 °C were less than those for the samples sintered at 1100 °C.

Synthesis of neodymium-doped barium nanoferrite: Analysis of structural, optical, morphological, and magnetic properties

Neodymium (Nd3+)-doped barium nanoferrite was synthesized by sonochemical method. The cation distribution of BaFe2O4 (BFO) nanoferrite is modified by doping of Nd3+ ions with different compositions (0≤ x ≤ 0.1; Δx = 0.025). Distinct changes in Raman active modes in the synthesized BaNdxFe2−xO4 nanoferrites were observed with a different composition of Nd3+ substitution. The elemental state of oxidation in the synthesized BaNdxFe2−xO4 nanoferrites was investigated. Ultraviolet diffuse reflectance spectroscopy indicated that the bandgap energy increases from 3.40 to 3.74 eV with an increase in Nd3+ concentration from 0 to 0.10. The dielectric constant values decreased with the addition of Nd3+ content. Room temperature hysteresis magnetic loop of the pure and Nd-doped BFO nanoferrites indicated that the saturation magnetization decrease with the addition of Nd3+ in BFO nanoferrites.

Influence of Zn-Zr substitution on the crystal chemistry and magnetic properties of CoFe2O4 nanoparticles synthesized by sol-gel method

The Zn-Zr co-substituted cobalt ferrite nanoparticles (CoZnxZrxFe2-2xO4, x = 0.0˗0.4) were synthesized by sol gel auto combustion route. The formation of cubic phase of Co ferrite was revealed from the X-ray diffractograms of the powder samples. The additional α-Fe2O3 and ZrO2 phases were occurred for ≥20% Zn-Zr substitution. The lattice parameters obtained by extrapolating Nelson–Riley function shows increase in its values with the Zn-Zr substitution. The particle size shows increasing trend with the Zn-Zr substitution. The cation distribution obtained from the Rietveld refinement of XRD estimate the equal preference of Zn ons preferred tetrahedral A site whereas most of the Zr ions occupy octahedral B site. The decrease in Fe ions with the Zn-Zr substitution resulted in the decrease in coercivity and saturation magnetization of the ferrites. Zero field cooled and field cooled magnetization plots of the ferrites reveals the ferromagnetic behaviour of the prepared ferrite samples. The blocking temperature does not vary significantly with the varying Zn-Zr substitution. The Mössbauer study confirms the weakening of the magnetic linkages between cations at A and B sites, due to the substitution of non-magnetic Zn-Zr ions for magnetic Fe ions. The decrease in coercivity with moderate saturation magnetization could make this material suitable for electronic devices.

Neutron diffraction study and magnetic properties of NiFe2-xScxO4

Polycrystalline NiFe2-xScxO4 (x = 0.00, 0.05 and 0.10) compounds were prepared using solid state reaction method. X-ray diffraction measurements revealed that the compounds exhibited cubic inverse spinel phase without any impurity phases. Room temperature neutron diffraction measurements were carried out to determine magnetic structure along with the structural properties. Raman measurements also supported the cubic inverse spinel ferrite structure of the compounds. The gradual shifts in wave numbers of prominent Raman modes indicated that the Sc3+ ions replaced Fe3+ ions at the B-site. A decrease in saturation magnetization (Ms), Curie temperature (Tc) and anisotropy constant of NiFe2-xScxO4 was observed with an increase of the Sc content.

Characterization of the iron oxide phases formed during the synthesis of core–shell FexOy@C nanoparticles modified with Ag

Core–shell FexOy@C nanoparticles (NPs) modified with Ag were studied with x-ray diffraction, transmission electron microscopy, energy dispersive elemental mapping, Mössbauer spectroscopy, static magnetic measurements, and optical magnetic circular dichroism (MCD). FexOy@C NPs synthesized by the pyrolysis process of the mixture of Fe(NO3)3 · 9H2O with oleylamine and oleic acid were added to a heated mixture of oleylamine and AgNO3 in different concentrations. The final product was a mixture of iron oxide crystalline NPs in an amorphous carbon shell and Ag crystalline NPs. The iron oxide NPs were presented by two magnetic phases with extremely close crystal structures: Fe3O4 and γ-Fe2O3. Ag is shown to form crystalline NPs located very close to the iron oxide NPs. An assumption is made about the formation of hybrid FexOy@C-Ag NPs. Correlations were obtained between the Ag concentration in the fabricated samples, their magnetic properties and the MCD spectrum shape. Introducing Ag led to a approximately linear decrease of the NPs saturation magnetization depending upon the Ag concentration, it also resulted into the MCD spectrum shift to the lower light wave energies. MCD was also studied for the Fe3O4@C NPs synthesized earlier with the same one-step process using different heat treatment temperatures, and MCD spectra were compared for two series of NPs. A possible contribution of the surface plasmon excitation in Ag NPs to the MCD spectrum of the FexOy@C-Ag NPs is discussed.

Structural Characteristics, Optical, Transport and Magnetic Properties of Zinc Doped Cobalt Chromium Ferrite Prepared by Co-precipitation Method

A series of zinc doped cobalt chromium ferrite Co1-xZnxFe1.5Cr0.5O4 (where 0 £ x £ 1) were synthesized by co-precipitation technique. Structural, optical, transport and magnetic properties were characterized by X-ray diffraction (XRD), diffuse reflectance, AC electrical properties and hysteresis loop. XRD analysis indicates that all samples consist of a single-phase cubic spinel structure. Rietveld refinement results indicated an increase in lattice parameter due to the replacement of Co2+ by Zn2+ and migration of Fe3+ ions from A-site to B-site. Optical energy band gaps were calculated and it was found that both Eg1 and Eg2 increase with increasing Zn content. Dielectric constant έ, έ', and dielectric loss tangent tanδ were measured at room temperature as a function of applied frequency and temperature. It was noticed, that έ and έ' increase with temperature increment and decrease with increasing frequency and this anomaly can be explained by Maxwell Wagner two-layer model. Magnetic measurements revealed that the saturation magnetization increases as Zn content increases up to Zn=0.4 and after that, the saturation magnetization decreases.

Enhancement in magnetoelectric properties of lead-free multiferroic composite through high-energy mechanical milling

Ferrite-Ferroelectric composites with the generic formula y(Mn0.5Cu0.5Fe2O4)1 − y[Ca0.1Ba0.9Zr0.1Ti0.9] (y = 25%, 50% and 75%) are prepared by solid-state reaction. One of the prepared samples of the composites 25%Mn0.5Cu0.5Fe2O4–75%Ca0.1Ba0.9Zr0.1Ti0.9O3 (MCF-CBZT) is subjected to high-energy mechanical milling for different durations (12 h, 18 h and 30 h). The compositional stoichiometry of all the samples is checked by Energy Dispersive Spectroscopy. All the un-milled and milled samples are characterized by X-ray diffraction, scanning electron microscopy, FTIR, magnetometry, and dielectric and magnetoelectric coefficient measurements. Magnetoelectric composite possesses biphasic surrounding to exhibit complex behavior of ME effect. The present study reveals influence of mechanical milling on MCF-CBZT magnetoelectric composite. The XRD confirms the presence of ferrite and ferroelectric phases for all the samples and microstructural changes appear in SEM images of milled specimens. FTIR spectra show four characteristic bands in 400–800 cm−1 range. Saturation magnetization and Curie temperature decrease as milling duration increases. Relaxed broad doublet with the distribution of nuclear hyperfine fields is found in Mossbauer spectra indicating good coupling between ferrite-ferroelectric phases caused by mechanical milling for the multiferroic composite. The frequency response of dielectric constant and loss tangent is recorded in the frequency range from 100 Hz to 1 MHz. The static value of magnetoelectric factor has been studied as a function of magnetic field for un-milled and milled MCF-CBZT samples. The maximum value 382 μV/cm·Oe of (ME)H is observed for the 18 h milled MCF-CBZT sample.

Magnetic Properties of Permalloy Thin Film Edges

The paper presents the results of ferromagnetic resonance (FMR) spectrometry of magnetic properties of nanocrystalline thin films obtained by magnetron sputtering of permalloy targets of various composition (NixFe1–x, x = 0.6–0.85). The behavior of the main magnetic properties of the thin film edges is analyzed. Near the film edges, not only the fluctuation of the uniaxial magnetic anisotropy field is observed, but also a drastic widening of the FMR line and the decrease in the effective saturation magnetization.

Effect of lanthanum doping on the structural, electrical, and magnetic properties of Mn0.5Cu0.5LaxFe2−xO4 nanoferrites

A sonochemical reactor was used to synthesize Mn0.5Cu0.5LaxFe2−xO4 (x = 0.025, 0.050, 0.075, and 0.100) nanoferrites. The structural, electrical, and magnetic properties were investigated for the samples using X-ray diffraction and vibrating sample magnetometer, and electrochemical impedance spectroscopy. The hysteresis analysis also reveals a unique soft ferromagnetic behavior for the studied nanoferrites. The doping of La3+ in Mn0.5Cu0.5LaxFe2-xO4 increases the bandgap energy, dielectric constant and coercivity while the field of saturation magnetization decreases. Reflection loss measurement reveals that these ferrites could be used as radiation absorption material in the X-band and Ku-band frequency.

Radiation impact of swift heavy ion beams on double-interface CoFeB/MgO magnetic tunnel junctions

A double-interface CoFeB/MgO magnetic tunnel junction (MTJ) has a high thermal stability barrier (E) and high-efficiency magnetization switching with the scaling of device dimensions. However, compared to a single-interface CoFeB/MgO MTJ, its more complicated film stacks and interfaces are more vulnerable to irradiation-induced swift heavy ions. We have studied the irradiation effects of Ta/Kr ions on double-interface CoFeB/MgO MTJs. Structural and physical analyses are performed through transmission electron microscopy, energy dispersive x-ray spectroscopy, and vibrating sample magnetometry. 1907 MeV Ta-ion irradiation damages the interfaces of the double-interface MTJ, resulting in the irreversible decrease in coercivity, while 2060 MeV Kr-ion irradiation damages the bulk properties of the MTJ, leading to the decrease in saturation magnetization. However, the electronic properties of the double-interface MTJ are almost immune to Kr-ion irradiation.

Effect of Mg-substitution in Co–Ni-Ferrites: Cation distribution and magnetic properties

We report the changes in structural and magnetic properties of spinel ferrites by doping magnesium, a cation that occupies the tetrahedral site, in place of nickel that occupies the octahedral site in Co–Ni ferrite (Co0.5Ni0.5Fe2O4) ceramic. We synthesized nano-crystalline Co0.5MgxNi0.5-xFe2O4 (x = 0, 0.1, 0.2, 0.3, 0.4) ceramic powder samples by sol-gel autocombustion method followed by calcination at 600 °C in air for 2 h. X-ray diffraction (XRD) patterns of the synthesized samples confirm crystalline single-phase spinel structure with cubic symmetry (Fd-3m space group). Refined structural parameters were calculated through Rietveld refinement of the XRD patterns. The crystallite sizes for all the samples were found to be in the range of 30–38 nm. Porous morphology of the samples was clearly observed from the scanning electron micrographs. The FTIR spectra confirm the formation of the spinel phase through the observed vibrational bands assigned to the tetrahedral (Td) and octahedral (Oh) interstitial complexes in the spinel structure. Magnetic measurements indicate a decrease of saturation magnetization (Ms) with increase in concentration of Mg. Room temperature 57Fe-Mössbauer spectroscopy in association with XRD results confirmed the ferrimagnetic nature of the samples with Mg occupying the Td site, Ni occupying the Oh site and Co occupying both the Td and Oh sites in the ratio of 2:3. Using the cation occupancies, Néel's two sublattice model could explain the observed magnetic properties in our Mg doped Co–Ni ferrite samples.