Nature Of Magnetic Interactions Research Articles

Magnetic interaction in Sr0.7La0.3Fe11.75Co0.25O19–CoFe2O4 composite system: observation, evidence, and influence

(100-x) Sr0.7La0.3Fe11.75Co0.25O19–(x) CoFe2O4 composites were synthesized by the one pot sol–gel auto-combustion method. The individual phase purity, morphology, and magnetic hysteresis loop of the composite magnet were analyzed by x-ray powder diffraction, field emission scanning electron microscopy and vibrating sample magnetometer, respectively. The apparent observation of the room temperature hysteresis loop indicates the existence of interfacial exchange interactions. Nevertheless, saturation magnetization (Ms ) follows the trend of Vegard’s law. The nature of magnetic interaction and its dependency on the amount of each phase were analyzed by employing the Thamm–Hesse plot. The critical size of the soft phase particle did not corroborate with the results of ΔM vs H plot. However, this synthesis method is found to be successful in obtaining single-step magnetization reversal in hard–soft composite magnets. The deviation from ideal non-interacting Stoner–Wohlfarth particles puts the single hard phase into the limelight. The (BH)max in the range of 1.07–0.98 MGOe has been obtained for the synthesized composite magnet.

Influence of composition on the structural, magnetic and magnetotransport properties of nanostructured Co-Ag films fabricated by electrodeposition technique

Evolution of structure, granular size, magnetoresistance and magnetization behavior of electrodeposited Co-Ag coatings with changing cobalt concentration from 19.07 to 47.02 at.% is offered. The heterogeneity of the deposits was verified through the utilization of structural techniques, including X-ray diffraction and transmission electron microscopy, revealing a size distribution ranging from superparamagnetic to ferromagnetic particles. The coatings were found to contain both fcc-Ag and fcc-Co. As the concentration of Co in the films increases, the size of the magnetic granules also increases while the distance among them simultaneously is reduced. The magnetic force microscopy indicates that magnetic domains exist which are significantly larger than actual particles. The highest giant magnetoresistance (GMR) amplitude was observed in coatings with a cobalt concentration of 33. 12 at. %. The studies on dc-magnetization obviously recognized the existence of perpendicular magnetic anisotropy. With increasing cobalt concentration beyond 33.12 at. %, the strength of perpendicular magnetic anisotropy decreases, while the anisotropic magnetoresistance (AMR) increases. The observed perpendicular magnetic anisotropy and complex magnetoresistance behavior in the Co-Ag films can be explained by the transition in the nature of magnetic interaction from dipolar to ferromagnetic interactions. Moreover, results indicate that the coercivity of Co-Ag films decreases with increasing the Co concentration up to 33.12 at. %, but begins to increase with further increasing Co concentration in the Co-Ag coatings. we calculated the first and second magnetic anisotropy factors based on the magnetization curves.

On the nature of the interlayer magnetic interactions in biphase ferromagnetic films

We report on the nature of the interlayer magnetic interactions in NiFe/Cu/Co films. By probing the quasi-static and dynamic magnetic properties of biphase ferromagnetic films, with soft and hard ferromagnetic phases intermediated by a non-magnetic layer, we address aspects of the coupling between magnetic layers. Our results demonstrate the nature of the interlayer magnetic coupling in biphase films. We also disclose the asymmetric magnetoimpedance effect as a fingerprint of the nature of the magnetic interlayer interactions playing key role in the magnetization dynamics of the system. We revisit in literature data and ideas on the asymmetric magnetoimpedance and the nature of the magnetic interactions in biphase ferromagnetic systems. Then, we compare our findings with results for biphase ribbons and microwires. Our observations raise the fundamental similarities and differences in the asymmetric magnetoimpedance of these structures.

Spectroscopic and magnetic investigations of the dilute magnetically doped semiconductors BaSn1-xMnxO3 (0.02 ≤ x ≤ 0.1)

Dilute magnetically doped semiconductors (DMSs) are key to fabricating novel spintronic devices with high functionalities, which could be utilized for the next-generation technological development. BaSnO3 is a transparent wide band gap (∼3.1 eV) semiconductor, in which magnetism can be induced through a subtle amount of magnetic impurity doping without deterring its optical transparency. In this work, we report an experimental investigation on the optical spectroscopic and magnetic properties of the DMSs BaSn1-xMnxO3 (0 ≤ x ≤ 0.1), synthesized using standard solid-state-reaction method at high-temperature and ambient pressure, through various spectroscopic, electron paramagnetic resonance (EPR) and temperature- and field-dependent magnetization measurements. All samples are found to be crystallize in the cubic structure with space group Pm3‾m, in which Mn ions are stabilized in the 4+ valence state. We find that the optical band gap monotonically decreases (from 3.1 eV to 2.08 eV) with increase in Mn doping concentration, which in turn leads to an increase in absorption efficiency in the visible region. An enhanced sp-d hybridization between localized d electrons of Mn ions and band electrons is likely the main reason for such band gap reduction. Interestingly, theoretical simulation of EPR spectra suggests that the signal is primarily arising from a combination of two spin systems, i.e., Mn4+ ions and singly ionized oxygen vacancies. The strength of magnetic interaction between Mn4+ ions is also increased for higher doped samples. Moreover, the nature of magnetic interaction is predominantly antiferromagnetic in higher doped samples, as corroborated by the negative value of Curie-Weiss temperature from the inverse susceptibility fitting.

Ferromagnetism in Mn doped 3C-SiC: A variable temperature ESR study

This paper discusses the effect of defects and role of charge carriers in setting up the long range magnetic order in Mn doped 3C-SiC. Using complementary experiments like temperature variation of Electron Spin Resonance (ESR) and DC magnetic susceptibility, the nature of magnetic interactions, spin dynamics and anisotropy have been investigated. The variation of ESR parameters such as, gvalue, peak to peak line width(ΔHpp), spin density (Ns) and spin–spin relaxation time (T2) as a function of temperature and dopant concentration confirms the presence of exchange interaction present in the system. The decrease in resonance field Hr as a function of temperature indicates the strengthening of internal field already existing in Mn doped 3C-SiC samples. This result confirms that defect induced magnetism could be enhanced by introducing holes in to the host wide band gap semiconductor.

Dielectric and magnetic properties of rare-earth-doped cobalt ferrites and their first-order reversal curve analysis

The present study focuses on the effects of rare-earth (R) ion substitutions namely Y, Sm and Pr ions on the structural, magnetic and electrical properties of cobalt ferrite (CFO) and the nature of their magnetic domains using the first-order reversal curve (FORC) analysis. These samples were synthesized using the sol–gel auto-combustion method. The powder X-ray diffraction analysis reveals that the Pr-substituted CFO crystallizes in a single-phase spinel structure, while a few traces of RFeO3 appear as minor phases in Sm- and Y-doped CFO. The scanning electron micrographs show that the substitution of R3+ ions causes a considerable reduction in the grain size. The studies on magnetic properties reveal that the saturation magnetization of R-substituted CFO decreased. The FORC analysis was done to know the domain state of magnetization and the nature of magnetic interactions among the grains. All the FORC diagrams depict a single peak with a single contour suggesting that all the synthesized samples have single domain particles and are comprised only of mono-magnetic phase. The electrical properties of the R-doped CFO compounds exhibit high values of dielectric constant at room temperature with the highest value for Pr-doped CFO. The activation energy determined using electrical properties is found to decrease with R doping.

Synthesis and thermal, optical and magnetic properties of new Mn2+-doped and Eu3+-co-doped scheelites

A series of Mn2+-doped and Eu3+-co-doped calcium molybdato-tungstates, i.e., Ca1−3x−yMny⌷xEu2x(MoO4)1−3x(WO4)3x (0 < x ≤ 0.2222 when y = 0.0200 and 0 < y ≤ 0.0667 when x = 0.1667, ⌷ represents vacancy) materials were successfully synthesized via high-temperature annealing. XRD results confirmed the formation of single, tetragonal scheelite-type phases (space group I41/a). A change in both lattice constants (a and c), lattice parameter ratio c/a and progressive deformation of MoO4/WO4 tetrahedra with increasing Eu3+ as well as Mn2+ contents were observed. The melting point of doped materials is lower than the melting point of pure matrix, i.e., CaMoO4. New materials exhibit strong absorption in the UV range. They are insulators with the optical direct band gap (Eg) higher than 3.50 eV. The Eg values nonlinearly change with increasing dopants concentrations. EPR measurements allowed to establish the nature of magnetic interactions among Mn2+ ions. Additionally, EPR spectra were sensitive on both parameters: Mn2+ and Eu3+ concentration.

Magnetic performances and switching behavior of Co-rich CoPtP micro-magnets for applications in magnetic MEMS

In this paper, the magnetic properties of Co-rich CoPtP films electrodeposited using an optimized Pulse Reverse (PR) technique are investigated for magnetic MEMS applications. By using a combination of forward and reverse pulses with optimized duty cycles during deposition and suitable bath chemistry, the film stress is reduced significantly, which results in smooth, crack-free films of thickness up to 26 μm. The deposited film of thickness ∼3 μm shows a coercivity of 268 kA/m, a remanence of 0.4 T, and a maximum energy product of 35 kJ/m3 in the out-of-plane direction. The variation in the hard-magnetic properties of the films for changing the film thickness is analyzed in terms of the composition, crystalline structure, and grain size. As the thickness is increased from 0.9 μm to 26 μm, the in-plane coercivity reduces by 17% due to an increase of the grain size and the Co content in the alloy structure. The in-plane squareness factor increases by 1.5 times as the thickness is increased over the above-mentioned range, which results in an enhancement of the in-plane remanence value. The magnetization reversal behavior of the deposited films indicates that the nature of magnetic interaction is significantly influenced by the thickness of the films, where the dipolar interaction for the thinner films changes to exchange coupling at higher thickness due to the increase of the grain size. Finally, an innovative design strategy to integrate CoPtP in magnetic MEMS devices by micro-patterning is proposed and analyzed using the finite element method. The demagnetization fields of the magnetic elements are minimized through optimized micro-patterned structures which improve the viability of PR deposited CoPtP micro-magnets having suitable nano-grains in potential MEMS based applications.

Energy product enhancement in sufficiently exchange-coupled nanocomposite ferrites

Ferrite based hard-soft magnetic nanocomposites with the composition of (100 − x) SrFe10Al2O19/(x) Co0.8Ni0.2Fe2O4, where x = 10, 15, 20 and 30 wt%, were prepared by one-pot sol-gel auto-combustion method. The nanocomposites prepared by this method showed crystallographically two phase behavior, but magnetically a good single phase exchange spring-coupled behavior with high saturation as well as high coercivity. The nature of magnetic interactions in these nanocomposites and their magnetic properties were evaluated in detail using various characteristic methods including vibrating sample magnetometer measurements, Henkel plots measurements, magnetic force microscopy and magneto-optical Kerr effect microscopy. Microstructural evolution showed formation of soft phase below the critical size of exchange length in the vicinity of hard phase. The nanocomposite with 15 wt% of soft phase showed a 10.5% increase in the maximum energy product compared to pure hard phase and reaches as high as 29.5 kJ/m3 that is a high value of (BH)max for this type of materials.

Critical behavior of the quasi-two-dimensional weak itinerant ferromagnet trigonal chromium telluride Cr0.62Te

The critical properties of flux-grown single-crystalline quasi-two-dimensional weak itinerant ferromagnet Cr$_{0.62}$Te were investigated by bulk dc magnetization around the paramagnetic (PM) to ferromagnetic (FM) phase transition. Critical exponents $\beta = 0.315(7)$ with a critical temperature $T_c = 230.6(3)$ K and $\gamma = 1.81(2)$ with $T_c = 229.1(1)$ K are obtained by the Kouvel-Fisher method whereas $\delta = 6.35(4)$ is obtained by a critical isotherm analysis at $T_c = 230$ K. With these obtained exponents, the magnetization-field-temperature curves collapse into two independent curves following a single scaling equation $M|\frac{T-T_c}{T_c}|^{-\beta} = f_\pm(H|\frac{T-T_c}{T_c}|^{-\beta\delta})$ around $T_c$, suggesting the reliability of the obtained exponents. Additionally, the determined exponents of Cr$_{0.62}$Te exhibit an Ising-like behavior with a change from short-range order to long-range order in the nature of magnetic interaction and with an extension from 2D to 3D on cooling through $T_c$.

Irreversible magnetization process and switching mechanism in L1 FePt thin films

The irreversible characteristics of the magnetization and the switching mechanism have been investigated in granular FePt films with L10 phase prepared by sputtering on a polymer substrate. The films display an extremely large magnetic anisotropy with a random distribution of the magnetization easy axis. The magnetic instabilities and the irreversible magnetization are found to be controlled by domain wall, which is responsible for the magnetization reversal. Through remanence curves and ΔM plot, the nature of magnetic interactions was revealed to be positive exchange coupling.

Syntheses, structures, and magnetic properties of a family of end-on azido-bridged CuII-LnIII complexes.

The reaction of Cu(valdmpn) (H2valdmpn = N,N'-bis-(3-methoxysalicylidene)-1,3-diamino-2,2-dimethylpropane), LnCl3·nH2O (Ln = La(1), Ce (2), Pr(3), Nd(4), Sm(5), Eu(6), Gd(7), Tb(8), Dy(9), Ho(10), Er(11), Tm(12), Yb(13), Lu(14)) and NaN3 in methanol led to a whole series of heterometallic CuII-LnIII complexes. The basic structural components of these complexes are the [CuII(valdmpn)LnIII] units with a compartmental Schiff-base ligand. These [CuIILnIII] units were then further connected by the end-on (EO) azides between the Ln3+ centers to form tetranuclear {[CuLn](μ-N3)n[LnCu]} motifs, where n is 3 for the complexes of larger radii lanthanides (1CuLa to 5CuSm) and 2 for the complexes of smaller radii lanthanides (6CuEu to 14CuLu). While compounds 6CuEu to 14CuLu remain isolated tetranuclear clusters, compounds 1CuLa to 5CuSm are one-dimensional chains where tetranuclear motifs are further connected by end-to-end (EE) azides between CuII and LnIII centers. Direct current (dc) magnetic susceptibilities have been measured in the range of 1.8-300 K for all complexes, revealing the different nature of magnetic interactions between the spin centers. Among them, dominant ferromagnetic interactions were found in compounds 7CuGd, 8CuTb and 9CuDy. Alternating current (ac) magnetic measurements performed on 8CuTb, 9CuDy, and 10CuHo demonstrated the presence of slow magnetic relaxation under zero applied dc field. The spin relaxation barrier Ueff was determined to be 19.54 cm-1 (28.12 K) and 10.34 cm-1 (14.87 K) for compounds 8CuTb and 9CuDy. The SMM behavior of 8CuTb was further confirmed by the presence of magnetic hysteresis loops; while no hysteresis loop was observed for 9CuDy and 10CuHo. These results demonstrated that azido-bridged copper(ii)-lanthanide(iii) complexes could be synthesized successfully despite the generally weak azido-lanthanide interaction.

Magnetic behaviour of Neodymium-substituted strontium hexaferrite

Neodymium-substituted strontium hexaferrites, Sr1−x Nd x Fe12O19 (x = 0, 0.05, 0.10, 0.15, 0.20), have been successfully synthesized by using citrate precursor method. The synthesized samples were characterized by X-ray diffraction, Transmission electron microscopy and vibrating sample magnetometry. The X-ray diffraction results show that the prepared samples are crystalline in nature and are of single phase with the space group P63/mmc. Transmission electron microscopy results show that the prepared sample is composed of fine nanoparticles with an average size of 80 nm. The effect on magnetic behaviour of strontium hexaferrite with neodymium substitution was analysed by using first-order reversal curves (FORCs). FORC analysis was done in order to know the domain state of magnetization of the nanoparticles and the nature of magnetic interactions among the particles. FORC diagrams depict a single peak, suggesting that the substituted systems are formed of interacting nanoparticles.

Spin states and glassy magnetism in LaCo1−xNixO3 (0 ≤ x ≤ 0.5)

We investigated the effect of Ni substitution on electronic structure and magnetic properties of perovskite LaCoO3 in the substitution range 0 ≤ x ≤ 0.5. A homovalent +3 state and spin state transition of Co+3 has been observed upon Ni substitution in x-ray absorption measurements at the Co and the Ni K-edges. Thermally driven spin state transition has been found to disappear with Ni substitution. A change in nature of magnetic interactions from antiferromagnetic to ferromagnetic and spin glass behavior with substitution is observed in dc and ac magnetization measurements. Ni substitution has been found to lower the average effective magnetic moment which has been ascribed to the decrease in Co/Ni ratio. Changes in fine structure and magnetic properties due to Ni substitution have been explained through the stabilization of intermediate spin state of Co+3 by the lattice expansion induced changes in crystal field. The Jahn-Teller distortion is assumed to be suppressed in the expanded lattice and possibility of antiferro-orbital ordering has been proposed for the ferromagnetic super-exchange interactions Co+3(IS)–O–Co+3(IS). The present work provides possible explanation for the ambiguity in the origin of FM in Co and Ni based perovskite cobaltites as well as supports the idea of lattice expansion induced ferromagnetism.

Electronic structure of the spin gapless material Co-doped PbPdO2

First-principles electronic structure calculations are performed for the pure and Co-doped PbPdO2 using plane wave density functional method using different exchange-correlation functionals. These calculations indicate the 25% Co-doped PbPdO2 to be a spin gapless semiconductor, as proposed earlier [X. L. Wang, Phys. Rev. Lett. 100, 156404 (2008)]. Insights into the nature of magnetic interaction between the Co-spins and its origin are developed through calculations over a wide range of Co concentrations.

ChemInform Abstract: Lessons Learned from Dinuclear Lanthanide Nano‐Magnets

AbstractReview: about 50 refs.

Influence of iron ions on the magnetic properties of CaO–SiO 2–P 2O 5–Na 2O–Fe 2O 3 glass–ceramics

Room temperature Electron Paramagnetic Resonance (EPR) spectra and temperature dependent magnetic susceptibility measurements have been performed on 41CaO.(52− x)SiO 2.4P 2O 5. xFe 2O 3.3Na 2O ( 2 ≤ x ≤ 10 mol % ) glass–ceramics. The parent glass samples were prepared by quenching the homogenized melt from 1550 ∘C. The glasses were then heat-treated at 1050 ∘C for 3 h and slowly cooled to room temperature to yield glass–ceramics. EPR and high temperature magnetic susceptibility measurements were made to elucidate the state of Fe +3 ions in the glass–ceramics. The EPR absorption line centered at g ≈ 4.3 disappeared at higher concentrations of Fe 2O 3. The intensity and linewidth of the absorption line centered at g ≈ 2.1 increased as the Fe 2O 3 concentration was increased. Information about the structural changes involving iron ions, their valence state and type of magnetic interactions between the Fe ions was obtained using EPR and magnetic susceptibility measurements. The temperature dependence of the magnetization of the glass–ceramics with low Fe 2O 3 concentrations exhibit both ferrimagnetic and paramagnetic contributions. The results obtained have been used to understand the structural changes occurring in the vicinity of iron ions and the nature of magnetic interactions between the iron ions in these glass–ceramics.

Dilution of two-dimensional antiferromagnetism by Mn site substitution inLa1Sr2Mn2−xAlxO7

We report the effect of Al substitution on the Mn site of the bilayered half doped manganite La{_1}Sr{_2}Mn{_2}O{_7}. This substitution dilutes the magnetically active Mn-O-Mn network without introducing an appreciable distortion in the lattice and ionic considerations leads to a predominant reduction of Mn{^{4+}} with increasing Al. The rate of fall of the long range antiferromagnetic transition temperature as a function of substitution is seen to match well with established quasi 2D Heisenberg systems indicating that the nature of magnetic interactions in this quasi 2-D system is of the short range Heisenberg type. The magnetic contribution of the specific heat estimated using Fisher's relation could be fitted with a function incorporating the presence of a gapped Fermi surface appropriate for this type of systems. The resistivity was seen to increase as a function of substitution due to the weakening of the double exchange within the ferromagnetic layers of these A type of antiferromagnets and justifiably, in the paramagnetic region the data could be fitted to Mott's equation for the variable range hopping of polarons in 2 dimensions.

A M ssbauer study of the magnetic coupling in iron phosphorous trisulfides

The polycrystalline sample of layered compound FePS3 has been investigated by using Mossbauer spectroscopy (12K to 300K), magnetic susceptibility measurements, x-ray diffraction and FTIR spectroscopy. The antiferromagnetic order exists below TN=120.5±1K. The Mossbauer spectra below TN indicate that the magnetization axis is perpendicular to the layer of {FePS}3 and the divalent iron cations are in their high spin configurations. By fitting the hyperfine field parameters near the Neel temperature, we obtain information on the nature of magnetic interactions in the material. The results show that the magnetic coupling can be treated by the two-dimensional Ising model and it can be interpreted on the basis of a crystal-field effect.

Magnetic coupling and site occupancy of impurities inFe3Al

Theoretical electronic-structure calculations have been carried out to examine the site occupancy of $3d$ transition-metal impurities in ${\mathrm{Fe}}_{3}\mathrm{Al}.$ Our studies based on the first-principles gradient-corrected density-functional formalism and carried over representative clusters show that the site occupancy is related to the strength and the nature of magnetic interactions. Impurities to the left of Fe couple antiferromagnetically to Fe and prefer ${\mathrm{Fe}}_{\mathrm{I}}$ sites while the impurities to the right (Co and Ni) couple ferromagnetically and prefer ${\mathrm{Fe}}_{\mathrm{II}}$ sites. The nature of coupling between impurities, Fe and Al sites is examined and its implications on controlling the magnetic behavior is highlighted.