Change In Magnetic Behavior Research Articles

Fe oxide modification of yerba mate waste-derived biochar and activated biochar via three methodologies: Effects of material surface properties on the Fe oxides grown and implications for paracetamol and atenolol sorption

This work presents, for the first time, the development of magnetic composites using activated biochar (BC-Act) derived from yerba mate waste. It includes an analysis of the effect of the activation process on the formation of iron oxides using the most applied methodologies, an aspect that has not been studied before. Three methodologies have been considered for Fe oxides grown: coprecipitation (COP), impregnation-pyrolysis (IP), and alkaline oxidation in the presence of nitrates (AOPN). The materials with magnetic response and good enough BET area have been used to sorb Paracetamol (PCT) and Atenolol (ATE) from aqueous solutions. The activation process has resulted in the formation of mesopores, an increase of surface area due to the destruction/release of impurities, the transformation of whewellite to calcite, and changes in magnetic behavior. These changes seem to affect the formation of Fe oxides. The COP and IP methods allow the development of magnetic composites based on BC-Act, BC-Act-COP and BC-Act-IP, with saturation magnetization of 3.1 Am2/kg and 1.5 Am2/kg, respectively, attributed to magnetite/maghemite formation and a minimal distance for manipulation by a magnetic field of 12.1 mm and 7.9 mm, respectively. These distances must be considered when developing efficient removal systems using magnetic composites. PCT was sorbed faster and more efficiently than ATE, associated with its smaller molecular size. This presents a valuable contribution to environmental sustainability and advancements in water purification, highlighting the dual advantage of converting the widely available waste product, predominantly found in South America, into an effective sorbent with magnetic characteristics, capable of removing pharmaceutical contaminants from aqueous solutions. This is done in the circular economy, avoiding the final deposition of yerba mate waste in landfills, increasing their lifespan, and safeguarding other natural and non-renewable resources, such as clays, whose preservation rather than exploitation improves environmental quality and saves energy.

Improving the Accuracy in the Prediction of Transition-Metal Spin-State Energetics Using a Robust Variation-Based Approach: Density Functional Theory, CASPT2 and MC-PDFT Applied to the Case Study of Tris-Diimine Fe(II) Complexes.

Designing ligands for transition metal complexes with a specified low-spin, high-spin or spin-crossover behavior is challenging. A major advance was recently made by Phan et al. [J. Am. Chem. Soc. 2017, 139, 6437-6447] who showed that the spin state of a homoleptic tris-diimine Fe(II) complex can be predicted from the N-N distance in the free diimine. They could thus predict the change in magnetic behavior on passing from the complexes of 2,2'-bipyridine (bpy), 2,2'-biimidazole (bim) and 2,2'-bis-2-imidazoline (bimz) ligands to those obtained with the modified analogs 4,5-diazafluoren-9-one (dafo), 1,1'-(α,α'-o-xylyl)-2,2'-bisimidazole (xbim) and 2,3,5,6,8,9-hexahydrodiimidazo[1,2-a:2', 1'-c]pyrazine (etbimz), respectively. Theoretically, the challenge lies in the accurate determination of the HS-LS zero-point energy difference ΔEHL°. The issue can be circumvented by using a variation-based approach, wherein ΔEHL° is not directly evaluated but obtained from the estimate of its variation Δ(ΔEHL°) in series of related systems, which include one whose ΔEHL° is accurately known [Phys. Chem. Chem. Phys. 2013, 15, 3752-3763; J. Phys. Chem. A 2022, 126, 6221-6235]. In this study, density functional theory (DFT), second-order multireference perturbation theory in its CASPT2 formulation, multiconfigurational pair DFT (MC-PDFT) and its hybrid formulation (HMC-PDFT) have been applied to the determination of Δ(ΔEHL°) in the pairs of complexes , , , and , . In DFT, we used several semilocal functionals and their global hybrids, as well as their D2, D3, D3BJ and D4 dispersion-corrected forms; and in MC-PDFT, different translated and fully translated functionals. The results are consistent with one another and in very good agreement with experiments. They show small to vanishing dependence on key details of the methods used: namely, the exact-exchange contribution to global hybrids; the ionization potential-electron affinity shift and basis sets used in the CASPT2 calculations; and the active spaces employed for the CASSCF wave functions used in the MC-PDFT and HMC-PDFT calculations. Insights into the change in the spin-state energetics accompanying the ligand exchanges were gained through a complexation energy analysis. Using the accurate CCSD(T) estimate of the HS-LS adiabatic energy difference in [J. Chem. Theory Comput. 2012, 8, 4216-4231], the Δ(ΔEHL°)-approach has been applied to the determination of ΔEHL° in the diimine complexes. The CASPT2 and DFT-D2 methods only give results in agreement with experiments. This suggests for the other methods a limitation in their treatment of dispersion which prevents them from accurately describing the spin-state energetics change accompanying the passing from with the tetragonal arrangement of its nitrile ligands to the tris-diimine complexes with the trigonal packing of their bulkier ligands.

DFT study of intrinsic mechanical properties of Mn2AlB2

Mechanically strong materials are vital components of a high temperature tribosystem. We used density functional theory to investigate the intrinsic elastic and plastic properties of Mn2AlB2- a novel MAB phase tribomaterial. The most vulnerable slip system and direction of Mn2AlB2 are (100)[100] and [001], respectively. The ideal shear strength of Mn2AlB2 is 18.75 GPa and its ideal tensile strength is 20.56 GPa. The deformation mechanisms of Mn2AlB2 are closely related to its magnetic and bonding properties. The shear deformation mechanism involves the breaking of old bonds (i.e. Al-B), formation of new bonds (i.e. Mn-Al, Al-Al (along the a-axis)) and anisotropy of the existing bonds (i.e. Mn-B(short) and B-B). The lattice instability of Mn2AlB2 at the critical strains is triggered by abrupt changes in its magnetic behavior and subtle changes in its bonding properties. The predicted mode I, II and III fracture toughness of Mn2AlB2 are 1.88 MPa.m1/2, 1.58 MPa.m1/2 and 1.40 MPa.m1/2, respectively. This study elucidates the intrinsic mechanical behavior of Mn2AlB2 in terms of lattice stability and plasticity under different loading conditions for extreme environment applications.

Fabrication, characterization, spectroscopic, and magnetic properties of polyaniline/magnetite (PANi/Fe3O4) nanocomposites

In this research, pure polyaniline (PANi), pure magnetite (Fe3O4), and then PANi/ Fe3O4 nanocomposites were prepared and characterized. FT-IR spectra of the prepared samples indicate successful polymerization of PANi onto Fe3O4. PANi/Fe3O4 nanocomposites exhibit broad absorption bands at specific wavenumbers, indicating the presence of various functional groups. The observed blue shift in certain peaks suggests the interaction between nitrogen atoms and oxygen atoms on the magnetite surface through hydrogen bonding. The intensity and wavenumber of the Fe3O4 band decrease, indicating weakened Fe–O bonds. These findings demonstrate a strong interaction and combination between PANi and Fe3O4 in the nanocomposites. Fe3O4 nanoparticles exhibit a regular spherical shape with an average diameter of 16 nm. However, they also show non-uniform size distribution due to aggregation into larger secondary particles, likely driven by attractive forces. PANi/Fe3O4 core-shell nanocomposites demonstrate clear morphological changes, with Fe3O4 nanoparticles well spread and wrapped by the PANi shell. The electron diffraction technique confirms the crystalline structure of Fe3O4 nanoparticles, showing diffraction rings consistent with magnetite. The results confirm the potential of incorporating magnetic Fe3O4 nanoparticles to impart magnetic functionality in the resulting PANi-based nanocomposite materials. Magnetic saturation measurements displayed an enhancement in magnetization with increasing Fe3O4 nanoparticles. The change in magnetic behavior for doped samples provides a means of tuning the magnetization strength of the composites to meet the application requirement such as data storage and magnetic sensors.

Local structure and defect analysis of KVO3 doped BiFeO3–BaTiO3 ceramics facing conductivity, permittivity, and magnetic properties

This study discovers the effects of KVO3 doping on BiFeO3–BaTiO3 regarding phase transitions, defect formation, and changes in electronic and magnetic behavior. The synthesized material (1-x-y)BiFeO3-xBaTiO3-yKVO3 with (x = 0.33, 0.38 and y = 0, 0.01) have pseudo-cubic structure, where the FeO6 octahedron was elongated in the z-axis, and Fe has an oxidation state of 3+ and 4+. The electrons in the 3d subshell initially showed a high spin state, transitioning to a low state after KVO3 doping. Further investigation identified phase transition Rhombohedral + Pseudo Cubic to Rhombohedral for FT33 at T∼100°C and Pseudo Cubic phase to Cubic phase for FT38 at T∼200°C. Conductivity at low temperatures ascribed to unbinding electrons, while the presence of defect-creating dipole strengthened the dipole polarization. The magnetization hysteresis of KVO3-doped samples significantly decreased due to the high spin state transformed to the low spin state of the 3d subshell of Fe in the octahedron FeO6.

Role of A site and B site ion substitutions on the low-temperature magnetic behaviour of Ca2Fe2O5

In the present paper, we report the structural and low-temperature magnetic properties of Sm-substituted Ca2Fe2O5 (Ca2(1-x)Sm2xFe2O5, x = 0.05, 0.1) and Co-substituted Ca2Fe2O5( Ca2Fe2(1-y)Co2yO5, y = 0.1, 0.2). The polycrystalline samples of Sm and Co-based compounds, synthesised by a solid-state reaction route, are found to be crystallised with space group Icmm and Pnma respectively. The gradual substitution/doping of Sm3+ (5 % and 10 %) replacing Ca shows a significant change in temperature dependant magnetic behaviour, assumed to originate from complex interactions of Sm and Fe ions. For Co-substituted samples, the magnetic study as a function of temperature suggests the signature of ferri/ferromagnetic interactions along with the probable signature of a glassy feature. Isothermal magnetisation characterisations indicate the pure antiferromagnetic interactions in Sm samples, whereas the onset of hysteresis in Co samples can be correlated with the ferri/ferromagnetic nature of samples with the antiferromagnetic ground state.

Unraveling the structural, electronic and magnetic properties of Mn1Pd n-1, Mn 2Pd n-2 and Pd n(n=13) clusters

This work presents a systematic study of the geometric, electronic and magnetic properties of Pd clusters pristine and mono- and bi[1]doped with Mn: Pdn, Pdn−1Mn, Pdn−2Mn2 where n ≤13. We have used the density functional formalism with the spin polarized generalized gradient approximation. From the variety of possible structures with thirteen atoms, we found the icosahedral configuration to be the most stable as compared to the hexagonal, cub-octahedral and buckled bi-planar. The change in magnetic behavior of Pd clusters after doping with Mn has been observed. This communication is an attempt to understand that behaviour.

Synthesis and Magnetic Studies of Two Neutral, Bis-Ligand Fe(II) Complexes Containing Carbazole-Bis(tetrazole) Ligands.

Previously reported carbazole-bis(tetrazole) (CzTR) ligands (where R = iPr and CH2-2,4,6-C6H2Me3) were used to synthesize air-stable, six-coordinate, octahedral bis-ligand Fe(II) complexes (CzTR)2Fe. The synthesis and characterization of these complexes using 1H nuclear magnetic resonance (NMR), X-ray crystallography, Mössbauer spectroscopy, and density functional theory (DFT) calculations are reported. Analysis of the magnetic properties revealed that the isopropyl derivative displays thermally induced spin crossover (SCO) over a temperature range of 150-350 K. This transition appears as an abrupt two-step transition in the solid state but simplifies to a smooth one-step transition in solution. The two-step transition in the solid state has been postulated to be due to lattice and solvation effects. In contrast, the slightly bulkier substituted CH2-2,4,6-C6H2Me3 (CH2Mes) Fe complex displays dramatically different magnetic behavior with no SCO and magnetic data suggesting low-spin Fe(II) with a possible TIP contribution. DFT calculations support the postulate that the change in magnetic behavior is primarily due to the nature of the ligand substituents.

Competing magnetic interactions, structure and magnetocaloric effect in Mn3Sn1-xZnxC antiperovskite carbides

Structural, magnetic and magnetocaloric properties of Mn3Sn1-xZnxC antiperovskite carbides have been studied. With increasing Zn content the first-order magnetic transition (FOMT) is weakened. The Curie temperature (TC) reduces first from 273 to 197 K and when x > 0.3, TC increases, reaching its maximum of 430 K for x = 1.0. An increase in TC is accompanied by pronounced changes in magnetic behaviour and a significant rise in magnetization from 21.82(4) to 76.2(2) Am2kg−1 for x = 0.8 in the maximum applied magnetic field of 5 T. Neutron powder diffraction (NPD) was employed to study the magnetic structure of Mn3Sn1-xZnxC compounds. The refinement of the NPD data for x = 0.3 revealed a magnetic structure with propagation vector k = (½,½,0) with a decrease in the canted antiferromagnetic (AFM) moment, which results in a reduction of the negative volume change at the magnetic transition and a decrease in the magnetocaloric effect (MCE). For x = 0.4, the magnetic structure is described by a propagation vector k = (½,½,½) for the AFM moment which dominates at low temperature, with the presence of a minor ferromagnetic (FM) component with a k = (0, 0, 0) propagation vector, which confirms the presence of the ferrimagnetic (FiM) state. For a higher Zn content (x = 0.6), the magnetic moment originates mainly from the FM component found on three independent Mn positions and an additional AFM moment oriented in the a-b plane. The results presented confirm the presence of competing AFM-FM interactions in Mn3Sn1-xZnxC antiperovskite carbides.

Effective and asymptotic criticality of structurally disordered magnets

Changes in magnetic critical behaviour of quenched structurally-disordered magnets are usually exemplified in experiments and in MC simulations by diluted systems consisting of magnetic and non-magnetic components. In our study we aim to show that similar effects can be observed not only for diluted magnets with non-magnetic impurities but may be implemented, e.g., by the presence of two (and more) chemically different magnetic components as well. Therefore we consider a model of the structurally-disordered quenched magnet where all lattice sites are occupied by Ising-like spins of different lengths L. In such a random spin length Ising model, the length L of each spin is a random variable governed by the distribution function p(L). We demonstrate that this model belongs to the universality class of the site-diluted Ising model. This proves that both models are described by the same values of asymptotic critical exponents. However, their effective critical behaviour differs. As a case study, we consider a quenched mixture of two different magnets with values of elementary magnetic moments L1=1 and L2=s, and of concentration c and 1−c, correspondingly. We apply field-theoretical renormalization group approach to analyse the renormalization group flow for different initial conditions, triggered by s and c, and to calculate effective critical exponents further away from the fixed points of the renormalization group transformation. We show how the effective exponents are governed by difference in properties of the magnetic components.

Fe-doping modulated critical behavior and magnetocaloric effect of magnetic Weyl Co3Sn2S2

${\mathrm{Co}}_{2.5}{\mathrm{Fe}}_{0.5}{\mathrm{Sn}}_{2}{\mathrm{S}}_{2}$ single crystal was grown by a flux method, and its magnetocaloric effect and critical behavior were systematically investigated. Significant changes in magnetic properties and critical behavior were observed in Fe-doped ${\mathrm{Co}}_{3}{\mathrm{Sn}}_{2}{\mathrm{S}}_{2}$, compared with undoped ${\mathrm{Co}}_{3}{\mathrm{Sn}}_{2}{\mathrm{S}}_{2}$. Specifically, the magnetization of ${\mathrm{Co}}_{2.5}{\mathrm{Fe}}_{0.5}{\mathrm{Sn}}_{2}{\mathrm{S}}_{2}$ measured at a low magnetic field ($H<500$ Oe, $H\ensuremath{\parallel}c$ axis) does not show the thermal hysteresis phenomenon, whereas it was observed in ${\mathrm{Co}}_{3}{\mathrm{Sn}}_{2}{\mathrm{S}}_{2}$ near ${T}_{\mathrm{c}}$, which is characteristic of a typical second-order phase transition. Previous reports usually attribute the suppression of ferromagnetism by the substitution of Fe for Co to the decrease in the number of $3d$ electrons. Herein, according to the first-principles calculation, the magnetic moments of dopant Fe align antiparallelly to those of Co atoms, which is also the possible reason for the decrease in magnetization. The critical behavior analysis shows that the critical exponents of the Fe-doped sample around magnetic transition are very close to theoretical values of the mean-field model. Furthermore, the exchange interaction distance $J(r)\ensuremath{\approx}{r}^{\ensuremath{-}4.65}$ and the Rhodes-Wolfarth ratio (RWR) (RWR > 1) prove the long-range itinerant ferromagnetism. The hybridization between the $3d$ orbitals of Fe/Co and the orbitals of $\mathrm{Sn}\text{\ensuremath{-}}5p/\mathrm{S}\text{\ensuremath{-}}3p$ may be an important factor for long-range itinerant ferromagnetism. The zero-field cooling magnetization ($H=100$ Oe, $H\ensuremath{\parallel}\phantom{\rule{0.16em}{0ex}}ab$ plane) undergoes the spin reorientation around 76 K, maybe because the magnetic moments of Fe, aligning antiparallelly to moments of Co atoms, reorient from out of plane to in plane. The critical behavior analysis shows that the first-order phase transition may occur below ${T}_{\mathrm{c}}$ in the case of the $H\ensuremath{\parallel}\phantom{\rule{0.16em}{0ex}}ab$ plane.

Preparation and magnetic properties of Co2-based Heusler alloy glass-coated microwires with high Curie temperature

In this article, we studied the effect of annealing (600 °C for 1 h) and the applied magnetic field from 50 Oe to 20 kOe of Co2FeSi glass-coated microwires with ordered L21 structure prepared by Taylor–Ulitovsky technique on the magnetic behavior. The as-prepared and annealed samples show a ferromagnetic behavior at the range of measuring temperature (5 to 400 K) and magnetic field (50 Oe to 20 kOe). M–H loops of as prepared sample do not show a squared shape. Meanwhile, perfectly squared hysteresis loops have detected for the annealed sample. In addition, annealed sample shows high magnetization M/M5K ratio, coercivity, and anisotropy field, as-compared to the as-prepared one. The annealed sample shows considerable irreversibility when the magnetic behavior changes with temperature upon the applied magnetic field at 50 and 200 Oe. Such irreversibility does not found in the as-prepared sample measured at the same magnetic field due to mixed amorphous and crystalline structure. By increasing the external magnetic field higher than 200 Oe and up to 20 kOe a gradual changing in the magnetic behavior has been detected where the irreversibility disappeared at applying magnetic field about 1 kOe and the magnetic behavior is totally change by increasing the external magnetic field up to the maximum 20 kOe. The difference in the magnetic behavior of the annealed glass-coated Co2FeSi glass-coated microwires indicates the effect of internal stresses induced by the presence of the glass-coating and the annealing-induced recrystallization.

Improved magnetic anisotropy of nano-crystalline Na substituted CaNb0.5Ti0.5O3 perovskite synthesized by sol–gel method

Polycrystalline samples of Ca1-xNaxNb0.5Ti0.5O3 were synthesized by sol–gel auto-combustion method. The impact of Na ions on the structural and magnetic properties of CaNb0.5Ti0.5O3 was investigated by X-ray diffraction (XRD), infrared spectroscopy (IR), scanning and transmission electron microscopy (SEM and TEM) and vibrating sample magnetometer (VSM) techniques. XRD data confirmed the perovskite nature of the prepared samples and showed the linear change in its crystallographic dimension upon Na substitution. Fourier transform infrared spectroscopy supports the XRD data, and help to study the vibrations associated with a particular bond type in the sample. SEM and TEM images confirmed the nano-crystalline nature of the prepared samples where average grain size of 110–120 nm and particle size of 60–70 nm is observed. Lattice fringes observed through TEM revealed the polycrystalline nature of the sample. d-spacing between the observed lattice fringes through TEM images also support the lattice planes observed via XRD data. Magnetic data obtained from VSM clearly demonstrate the change in magnetic behaviour of CaNb0.5Ti0.5O3 upon Na substitution. Na ion substitution improves the magnetic interaction in CaNb0.5Ti0.5O3 by improving the magnetization value.

Spin Crossover Coordination Polymers with Pyridine-Like Modification through Selective Guest Molecules

A porous 3D FeII coordination polymer made of 4,4′-bipyridine ligands (bipy) and [N(CN)2]− (dca) organic bridges, [Fe(bipy)2dca]ClO4·CHCl3·CH3OH (1·CHCl3·CH3OH), has been synthesized as single crystals, by a slow diffusion technique at room temperature. Single-crystal X-ray diffraction analysis has shown that the structure of 1·CHCl3·CH3OH presents large volume values of porosity (1790 Å3 per iron atom). It crystallizes in the orthorhombic Cmc21 space group but undergoes a phase transition to Cmca at 298 K, presumably due to solvent release. According to magnetic data, this material displays a gradual spin crossover behavior, along with a thermal hysteresis loop of 15 K around 190 K. However, when lattice solvent molecules are removed, the magnetic behavior changes drastically resulting in more gradual spin conversion or even silencing the spin crossover behavior of the as-synthesized complex (1·CHCl3·CH3OH), evidencing the influence of guest molecules on the magnetic properties by host–guest interactions. This property was confirmed by spatiotemporal optical microscopy studies, performed on several single crystals. The generation of a host lattice that interacts with exchangeable guest species in a switchable fashion has implications for the generation of previously undeveloped advanced materials with applications in areas such as molecular sensing.

Chemical Exfoliation toward Magnetic 2D VOCl Monolayers.

The diversification of magnetic two-dimensional (2D) materials holds the key to the further development of advanced technologies, such as spintronic devices and efficient data storage. However, the search for intrinsic magnetism down to the 2D limit is severely limited by the ability to reliably exfoliate large, air-stable nanosheets. Chemical exfoliation, a relatively underutilized method for delamination, offers many advantages, including a high degree of adaptability and higher yields of uniformly exfoliated materials. van der Waals (vdW) materials, in particular the family of transition-metal oxyhalides, are ideal candidates for chemical exfoliation due to their large interlayer spacing and the wide variety of interesting magnetic properties they exhibit. In this study, we employ a chemical exfoliation method to delaminate the layered antiferromagnet vanadium oxychloride (VOCl) down to the monolayer limit. The resulting nansoheets have lateral sizes of up to 20 μm, are air-stable, and can be easily isolated. Magnetic characterization was performed throughout the exfoliation process, tracking the changes in magnetic behavior among bulk VOCl, its lithiated intercalate, and the restacked nanosheet pellet. The results from this work demonstrate the potential of chemical exfoliation, along with illustrating the effects of low dimensionality on magnetic properties.

Resolving magnetic contributions in BiFeO3 nanoparticles using First order reversal curves

BiFeO3 (BFO) nanoparticles (NPs) were studied using First-Order Reversal Curve (FORC) and temperature-dependent magnetometry measurements. The BFO NPs were fabricated by a sol–gel method, while the crystal structure and the average particle radius were obtained by powder X-ray diffraction analysis and Small-Angle X-Ray Scattering (SAXS) measurements, respectively. The NP size varies below and above the typical bulk BFO spin cycloid length (λ= 62 nm). Below λ, the NPs show ferromagnetic-like hysteresis loops where the saturation magnetization decreases while nanoparticle size rises. This magnetic behavior changes for NP size over λ, which only exhibits a paramagnetic contribution. The FORC distributions indicate the presence of two competing size-dependent contributions to the observed magnetic signal Also, the FORC distributions show that in the ferromagnetic regime there are two competing size-dependent contributions to the observed magnetic signal. Our results suggest the existence of a magnetic core–shell structure in NPs below λ, possibly driven by the strong spin–lattice coupling.

Annealing effects on NiO nanoparticles for magnetic behaviour and antibacterial activity

The aim of this work is to synthesise nickel (II) oxide (NiO) nanoparticles through the co-precipitation method and study their applications. Thermal gravimetric analysis was used to measure the thermal stability of the synthesised nanoparticles. The X-ray diffraction patterns of nickel (II) oxide showed a face-centred cubic structure and an average crystallite size of 16–36 nm. Fourier transform infrared spectra confirmed the formation of Ni–O bonds. The surface morphology was analysed using scanning electron microscopy. The mean particle size was about 50.76 nm, measured from high-resolution transmission electron microscopy images. The elements present in the samples were identified using energy-dispersive X-ray analysis. Vibrating-sample magnetometer analysis was used to determine the changes in magnetic behaviour of nickel (II) oxide nanoparticles due to an annealing temperature increase. As regards the antibacterial activities of nickel (II) oxide nanoparticles against Escherichia coli and Staphylococcus aureus bacterial strains, it was found that the zone of inhibition expanded as the nanoparticle concentration increased.

Composition and magnetic properties of thin films grown by interdiffusion of Mn and Sn-Rich, Ge lattice matched SixGe1-x-ySny layers

We report on the structure and magnetic properties of Mn based ferromagnetic layers on the semiconductor SixGe1-x-ySny with Sn content up to y = 0.15 in comparison with layers on Ge and Si0.75Ge0.25. The ferromagnetic layers grow by interdiffusion between an evaporated Mn layer and molecular-beam-epitaxy grown semiconductor layers. This approach enables the preparation of Mn based layers, e.g., as a ferromagnetic contact material for SixGe1-x-ySny using a self-aligned interdiffusion process, opening up the opportunity for large-scale manufacturing. The samples show a clear phase separation into Si-rich and Ge-rich Mn compounds. All samples are ferromagnetic and exhibit a decrease in saturation magnetization and an increase in coercive field with increasing Si content x. The Curie temperature shows no decisive trend with increasing Si content with values around room temperature. Based on the composition, structure and magnetic properties, we propose a two-layer model to correlate the structure and composition with the observed magnetic properties. We show that the changes in magnetic behavior can be explained solely by considering the Si content of the SixGe1-x-ySny substrates with the Sn being largely passive.

Role of Fe (x = 0–0.15) Substitution on Structural, Magnetic, and Transport Properties of the La0.7Sr0.3FexMn1−xO3 System

This paper investigates the effect of Fe substitution on the structural, magnetic and transport properties of the La0.7Sr0.3MnxFe1−xO3 (LSMO) system where x ranged between 0 and 0.15. Samples were prepared using a non-aqueous sol-gel synthesis method. Structural and chemical analysis confirmed the Fe3+ substitution at Mn3+ sites without any impurity phase resulted in a small change in structural parameters of the LSMO. The change in magnetic behavior and Curie temperature of the Fe-doped LSMO is explained through competitive exchange interactions developed in the system. The temperature-dependent resistivity demonstrated that the resistivity of the samples increased with Fe concentration due to different conduction mechanisms related to the ferromagnetic-metallic and paramagnetic-insulating regions. The magneto-transport measurement showed significant improvement in the magnetoresistance due to Fe doping at Mn site, which was attributed to enhancement of the spin-glass phase in Fe doped LSMO system. The reduction in magnetoresistance for higher Fe concentration is explained with the help of percolation threshold mechanism.

Growth behavior, physical structure, and magnetic properties of iron deposited on Tris(8-hydroxy quinoline)-aluminum

Growth behavior and evolution of magnetism as a function of Fe thin film thickness onto organic semiconductor tris(8-hydroxyquinoline)-aluminum, (Alq3) thin film was investigated in-situ using electrical resistance and magneto-optic Kerr effect (MOKE) measurements, respectively. The variation of electrical resistance with Fe film thickness reveals the Volmer-Weber growth of Fe on Alq3 film. Reflection high energy electron diffraction (RHEED) pattern resembles polycrystalline BCC structure of Fe. Ex-situ x-ray reflectivity (XRR) measurement from the Fe/Alq3/Si sample reveals that Fe diffuses into Alq3 to form an alloy layer of 50 Å thickness with Fe volume fraction of 0.4. In-situ MOKE study affirms anomalous magnetic behavior at the initial stage of Fe growth. Initially hysteresis loop appears and develops in a particular direction, and then vanishes at certain thickness. With further growth of Fe hysteresis loop appears again and grows in the opposite direction. The observed unusual changes in magnetic behavior as a function of Fe thickness may be explained in terms of the contribution from the magnetic Fe-Alq3 alloy present in the intermix layer, the metallic Fe on top of Alq3 layer, and their antiferromagnetic coupling.