Ferrimagnetic Properties Research Articles

Compositional dependence of structural, magnetic and spin-phonon coupling properties in Fe2−xGaxO3 (x = 0.6–1.2) system with orthorhombic symmetry

A combined technique of mechanical alloying and heat treatment has been used to prepare the polycrystalline samples of Fe2−xGaxO3 (x = 0.6–1.2) system in orthorhombic phase. It has been possible to reduce the sintering temperature by ~350 °C for stabilizing the orthorhombic phase in comparison to the temperature reported in literature. The Rietveld refinement of X-ray diffraction patterns indicated the distribution of Ga and Fe atoms in the Ga1, Ga2, Fe1 and Fe2 sites of the lattice structure. A linear variation of the lattice parameters with Ga/Fe content showed application of Vegard’s law. The temperature-dependent magnetization measurements confirmed ferrimagnetic order of Fe spin moments. The ferrimagnetic transition temperature (TC) has decreased from 320 K to 100 K with the increase of Ga content in the range of x = 0.6–1.2. Temperature-dependent Raman spectroscopy data ruled out any structural phase transition at TC, but an anomalous behaviour of the position and width of the peaks of Raman active phonon modes near to TC confirmed a strong spin–phonon coupling in the material. The spin–phonon coupling strength (η) for the A9 mode has been found around 1.64 cm−1 for x = 1 and 3.34 cm−1 for x = 0.8, and η for the A21 mode has been found around 2.12 cm−1 for x = 1 and 3.28 cm−1 for x = 0.8. The spin-phonon coupling strength has been diluted in the samples with higher content of Ga. The experimental results indicated that the variation of Ga/Fe content and its distribution in lattice sites determine the ferrimagnetic properties, magnetic anisotropy and spin-phonon coupling in Fe2−xGaxO3 system. The results are expected to be useful for understanding the spin-phonon coupling in multiferroic-magnetoelectric materials with magnetic and electric transitions near to room temperature.

Epitaxial Ferrimagnetic Mn4N Thin Films on GaN by Molecular Beam Epitaxy

Direct epitaxial integration of magnetic layers with wide bandgap nitride semiconductors will enable spin-controlled transport and photonic phenomena, seeding ideas for functional spintronic devices. Using plasma-assisted molecular beam epitaxy (MBE) in a previously unexplored window, significantly improved ferrimagnetic Mn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> N layers are successfully grown on GaN with ~1 nm surface roughness. Distinct from earlier reports, the Mn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> N layers grown on GaN are found to be [001] oriented with 12-fold in-plane symmetry in the diffraction pattern. This unique epitaxial registry originates from three equivalent rotational domains. The ferrimagnetic magnetotransport properties of low growth temperature Mn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> N layers on GaN are comparable to those reported on cubic substrates such as MgO. However, a sign-flip of the Hall resistance is discovered for Mn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> N layers grown above 300 °C.

Quaternary Selenides EuLnCuSe3: Synthesis, Structures, Properties and In Silico Studies.

In this work, we report on the synthesis, in-depth crystal structure studies as well as optical and magnetic properties of newly synthesized heterometallic quaternary selenides of the Eu+2Ln+3Cu+1Se3 composition. Crystal structures of the obtained compounds were refined by the derivative difference minimization (DDM) method from the powder X-ray diffraction data. The structures are found to belong to orthorhombic space groups Pnma (structure type Ba2MnS3 for EuLaCuSe3 and structure type Eu2CuS3 for EuLnCuSe3, where Ln = Sm, Gd, Tb, Dy, Ho and Y) and Cmcm (structure type KZrCuS3 for EuLnCuSe3, where Ln = Tm, Yb and Lu). Space groups Pnma and Cmcm were delimited based on the tolerance factor t’, and vibrational spectroscopy additionally confirmed the formation of three structural types. With a decrease in the ionic radius of Ln3+ in the reported structures, the distortion of the (LnCuSe3) layers decreases, and a gradual formation of the more symmetric structure occurs in the sequence Ba2MnS3 → Eu2CuS3 → KZrCuS3. According to magnetic studies, compounds EuLnCuSe3 (Ln = Tb, Dy, Ho and Tm) each exhibit ferrimagnetic properties with transition temperatures ranging from 4.7 to 6.3 K. A negative magnetization effect is observed for compound EuHoCuSe3 at temperatures below 4.8 K. The magnetic properties of the discussed selenides and isostructural sulfides were compared. The direct optical band gaps for EuLnCuSe3, subtracted from the corresponding diffuse reflectance spectra, were found to be 1.87–2.09 eV. Deviation between experimental and calculated band gaps is ascribed to lower d states of Eu2+ in the crystal field of EuLnCuSe3, while anomalous narrowing of the band gap of EuYbCuSe3 is explained by the low-lying charge-transfer state. Ab initio calculations of the crystal structures, elastic properties and phonon spectra of the reported compounds were performed.

Role of structural dimensionality in the magneto-chiral dichroism of chiral molecular ferrimagnets

The optical and magneto-chiral optical properties of a 3D chiral molecular ferrimagnet based on CrIII and MnII building blocks have been investigated to unveil the role of structural dimensionality on magneto-chiral dichroism.

Ferrimagnetism and reentrant behavior in a coronene-like superlattice with double-layer

Phase diagrams and temperature dependences of magnetizations in a coronene-like lattice have been studied based on the effective-field theory with correlations. For the spin-3/2 and 2 atoms in the superlattice with double-layer Ising model, both the transverse field and anisotropy are included. Novel features, such as the possibility of compensation and reentrant behaviors, are found for the ferrimagnetic properties in such systems.

Self-assembly of 1D FeSe2 chains and Fe(dien)2 complexes for ferrimagnetic inorganic-organic hybrid cuboids

Challenges still remain in producing room-temperature ferromagnetism/ferrimagnetism in inorganic–organic hybrid compounds. Here, we report the Fe vacancy-doped inorganic–organic (FexSe2)2Fe(dien)2 (dien = diethylenetriamine, x = 0.86) hybrid cuboids by self-assemble of finite one-dimensional (1D) FeSe2 chains and Fe(dien)2 complexes. A growth model is proposed by kinetically controllable syntheses of novel Fe2x+1Se4(dien)2 hybrids. The Rietveld refinement reveals that Fe vacancies in the Fe2.71Se4(dien)2 hybrid cuboids induce large distortions of the FeSe2 chains and the room-temperature lattice parameters are a = 9.225(4) Å, b = 18.021(8) Å and c = 11.609(6) Å. Magnetic measurements and electron spin resonance spectra of the Fe2.71Se4(dien)2 hybrid cuboids show the ferrimagnetism with the Curie temperature (TC) of 600 K and the spin glass state with the freezing temperature (Tf) of 108 K. Impressive room-temperature ferrimagnetic properties of the Fe2.71Se4(dien)2 hybrid cuboids were ascribed to the high concentration of Fe3+ vacancies (0.29 per cell) in the hybrid cuboids, which is supported by the 57Fe Mössbauer spectrum fitting based on the ferrimagnetic model.

Effects of co-substitution of Al3+ and Cr3+ on structural and magnetic properties of nano-crystalline CoFe2O4 synthesized by the sucrose technique

Al–Cr substituted CoFe2O4 nano spinels (CoAlxCrxFe2−2xO4 where x = 0.1 to 0.6) were successfully prepared for the first time via sucrose sol–gel auto-combustion technique. The structural parameters as well as magnetic and electrical properties of the prepared ferrites have been investigated. X-ray diffraction (XRD) confirmed single-phase formation and showed a decrease in the calculated values of lattice parameters by substitution attributed to the difference in the ionic radii. Based on the obtained structural parameters, an appropriate cation distribution was proposed and discussed. In this distribution, most of Al3+ and Cr3+ ions preferred octahedral sites occupation however, small amount of Al3+ seek the tetrahedral sites. Accordingly, the magnetic characterization via vibrating sample magnetometer (VSM) measurements revealed a decrease in the saturation magnetization (Ms) by successive substitution from 57.9 to 4.7 emu/g, indicating the incorporation of non-magnetic Al3+ and anti-ferromagnetic Cr3+ ions in the octahedral sites instead of Fe3+ ions. The much lower magnetization values obtained than that prepared by other methods could be attributed to the present lower sizes. The coercivity measurements indicated soft ferrimagnetic properties favoring their uses as high frequency transformers. Ac-conductivity as well as dielectric properties, as a function of frequency and temperature, indicated semiconducting behavior with decreasing trend by Al–Cr substitution due to decreasing in the Fe3+-Fe2+ hopping probability in octahedral sites. The obtained results suggest the using of the present materials in electronic inductors, electromagnets and transformers and microwave devices.

Experimental demonstration of a concave grating for spin waves in the Rowland arrangement

We experimentally demonstrate the operation of a Rowland-type concave grating for spin waves, with potential application as a microwave spectrometer. In this device geometry, spin waves are coherently excited on a diffraction grating and form an interference pattern that focuses spin waves to a point corresponding to their frequency. The diffraction grating was created by focused-ion-beam irradiation, which was found to locally eliminate the ferrimagnetic properties of YIG, without removing the material. We found that in our experiments spin waves were created by an indirect excitation mechanism, by exploiting nonlinear resonance between the grating and the coplanar waveguide. Although our demonstration does not include separation of multiple frequency components, since this is not possible if the nonlinear excitation mechanism is used, we believe that using linear excitation the same device geometry could be used as a spectrometer. Our work paves the way for complex spin-wave optic devices—chips that replicate the functionality of integrated optical devices on a chip-scale.

Hyperthermia of breast cancer tumor using graphene oxide-cobalt ferrite magnetic nanoparticles in mice

Herein, the graphene oxide (GO)/cobalt ferrite nanoparticles were used to apply the heat treatment on the breast cancer cell line of MCF7. The synthesized nanoparticles were evaluated before in vitro and in vivo studies, using transmission electron microscopy (TEM), X-ray diffraction (XRD), vibrating sample magnetometer (VSM), X-ray photoelectron spectroscopy (XPS), thermal property and relaxivity measurement. The nanoparticles showed a diameter of 5 nm with the ferrimagnetic property. Also, the nanoparticles were well distributed on the GO nanosheets. The related peaks of cobalt ferrite nanoparticles were approved by using XRD and XPS assays. During the in vitro investigations, IC50 with the cell survival of 58% was obtained after 72 h treatment with the nanoparticles. However, the cell viability value was decreased to 30% after applying the hyperthermia process. Moreover, the in vivo studies were performed using BALB/c mice and the results indicated the smaller size of the tumor with the concentrations of 0.001 and 0.002 gr/ml and the respective magnetic frequencies of 400 and 250 kHz for 10 min after 27 days. The magnetic resonance imaging (MRI) studies also confirmed the presence of the nanoparticles not only within the tumor, but also in other tissues. The molecular gene expression of the treated tumor showed the higher expression of apoptotic genes. On the other hand, the hematoxylin and eosin (H&E) staining approved that the tumor cytoskeleton was ruined specially by the nanoparticle concentration of 0.002 gr/ml at the frequency of 250 and 350 kHz. As a whole, the findings could recommend a useful therapeutic strategy of the hyperthermia by using the magnetic nanoparticles.

Tuning Exchange Coupling in NiO-Based Bimagnetic Heterostructured Nanocrystals.

A series of bimagnetic heterostructured nanocrystals having an antiferromagnetic NiO core and a ferrimagnetic MnxNi1-xO and/or FiM Mn3O4 island nanophase overgrowth has been synthesized under varying aqueous solution pH conditions. The two-step self-assembly process employs a thermal decomposition method to synthesize NiO nanoparticles, followed by growth of the MnxNi1-xO and/or Mn3O4 nanophase over the NiO core using hydrothermal synthesis at pH values ranging from 2.4-7.0. The environmentally benign hydrothermal process involves pH control of the protonation vs hydroxylation reactions occurring at the nanoparticle surface. TEM analysis and Rietveld refinement of XRD data show that three distinct types of heterostructured nanocrystals occur: NiO/MnxNi1-xO core-shell-like heterostructures at the pH of 2.4, mixed NiO/MnxNi1-xO and/or/Mn3O4 core-overgrowth structures for 2.4 < pH < 4.5, and predominantly NiO/Mn3O4 core-island structures for pH > 4.5. The magnetic coercivity and exchange bias of the heterostructured nanocrystals vary systematically with the pH of the aqueous solution used to synthesize the samples. The temperature-dependent magnetization and hysteresis loop data are consistent with the nature of overlayer coverage of the NiO core. Our DFT based calculations show that the MnxNi1-xO phase has ferrimagnetic properties with a stable spin orientation along the ⟨111⟩ orientation. Furthermore, the calculations show that the magnetic anisotropy constant (K1) of the Mn3O4 phase is considerably larger than that of the MnxNi1-xO phase, which is confirmed by our experimental results. The coercivity and exchange bias field are the largest for the NiO/Mn3O4 core-island nanocrystals, synthesized at a pH value of 5.0, with robust values of nearly 6 kOe and 3 kOe, respectively. This work demonstrates the tunability of hydrothermal deposition, and concomitant magnetic coercivity and exchange bias properties, of MnxNi1-xO and/or Mn3O4 nanophase overgrowth over a NiO core with pH, that makes these heterostructured nanocrystals potentially useful for magnetic device, biomedical, and other applications.

Existence of two spin dynamics in the temperature and magnetic field dependence of the magnetization curves of ferrimagnetic Co1.75Fe1.25O4 and its composite with BaTiO3

The present work describes ferrimagnetic properties of spinel oxide Co1.75Fe1.25O4 (CFO) and its composite (CFO_BTO) with ferroelectric and non-magnetic BaTiO3 (BTO). Rietveld refinement of the synchrotron X-ray diffraction patterns provided detailed structural phase information of the CFO and CFO_BTO samples. The dc magnetization measurements confirmed blocking temperature of the samples around 300 K for applied magnetic field 500 Oe and exchange bias effect at 5 K. On the other hand, both the samples exhibited a strong magnetic memory effect at around 250 K and the memory effect gradually suppressed at low temperatures. Apart from conventional modifications of magnetic moment and coercivity in composite system with reference to pure spinel ferrite system, the present work has shown that ferrimagnetic parameters can be varied by adopting some unconventional measurement protocols, where time dependent magnetization has been recorded during measurements of the temperature and field dependent magnetization curves. The analysis of waiting time dependent magnetization data confirmed the existence of two non-equilibrium spin dynamics, defined by different time constants, both in CFO ferrite and CFO_BTO composite systems. The measurements also confirmed the dilution of magnetic exchange interaction and faster spin relaxation in the composite system.

Synthesis, Composition, and Magnetic Properties of Cadmium-Doped Lanthanum Ferrite Nanopowders

Nanocrystalline La1 – xCdxFeO3 (x = 0, 0.05, 0.1, 0.15, 0.2) powders with a narrow homogeneity range (xmax = 0.09 according to X-ray microanalysis and X-ray diffraction data) have been synthesized via coprecipitation followed by thermal annealing at 950°C for 1 h. The addition of Cd2+ cations leads to a decrease in average crystallite size from 10–70 nm at x = 0 to 5–60 nm at x = 0.1 (according to transmission electron microscopy data). The synthesized nanocrystals have ferrimagnetic properties.

Enhanced electrical and ferrimagnetic properties of bismuth substituted yttrium iron garnets

Y3-xBixFe5O12 (0 ≤ x ≤ 1.0) powders are successfully prepared by sol-gel auto-combustion method. The structural, morphological, electrical and magnetic properties of bismuth substituted YIG are systematically studied and reported. The phase formation and position of vibrational modes are studied using XRD, FTIR and Raman Spectroscopy respectively. The XRD patterns of Bi-YIG powders confirm the formation of polycrystalline, single phasic and cubic garnet structure with average crystallite size around 39 nm. FTIR spectra show well resolved bands corresponding to the tetrahedral and octahedral voids of Fe–O in YIG which is characteristic of garnets. The observed translational Raman active vibrational modes confirm the presence of cubic YIG phase. SEM micrographs reveal the formation of adense homogenous network of spherical shaped Y3-xBixFe5O12 grains. Magnetic properties of Bi-YIG show an enhancement compared to the host YIG, confirming the presence of ferrimagnetic ordering at room temperature. The observation of hysteresis loop along with low coercivities are typical of soft magnetic materials. Impedance measurements of Bi-YIG show an increase in electrical resistance up to two orders compared to YIG. The Bi-YIG sample having x = 0.6 exhibits a low dielectric loss equal to 0.045 and a low conductivity of the order of 10−6 Scm−1 at 100 kHz. The observations from magnetic and electrical studies illustrate the distinct role played by bismuth ions in the YIG lattice making it a potential candidate for microwave and magnetic-optical applications.

(111), (001), and (110) surface effects on the stability and electronic-magnetic properties of Mn3P alloy

Abstract In this theoretical study, we predict the (111), (001), and (110) Mn3P compounds with a DO3-Type-structure. We first calculated the stability, and surface effects on the pure terminations of Mn3P (111), (001), and (110) surfaces using first-principle computations. Pure (111), (110), as well as the Mn2 -(001) terminations, lose their half-metallic (HM) ferrimagnetic property, with higher spin polarization (SP) (75%) for Mn 2-(111) than for the other terminations. These terminations present metallic properties because the spin-up and spin-down pass the Fermi level (єF). The Mn1–P termination remained HM with full SP; this is because of the strong coupling between the surface and subsurface, which indicates that this surface is a typical candidate for spin devices. The spin magnetic moments (SMMs) were investigated in all surface states. The SMM values of the central layers of the (111), (001), and (110) terminations were similar to those in the bulk, while the SMMs in the surface layer were higher than those in the bulk Mn3P.

Synthesis of BaTiO3-CoFe2O4 nanocomposites using a one-pot technique

Low-cost and scalable sol–gel chemistry was employed to obtain ferroelectric-ferrimagnetic BaTiO3-CoFe2O4 nanocomposites. In a novel one-pot synthesis method, both the constituent phases of nanocomposites are formed during the same time and symbiotically participate to each other’s growth. X-ray powder diffraction evidences the phase purity of the systems, with average crystallite sizes in the order of 20 nm for the BaTiO3 phase. The optimization of the synthesis conditions, precursors, and chemical agents for nanoscale BaTiO3 and BaTiO3-CoFe2O4 nanocomposites is presented, together with the magnetic and/or dielectric properties of the obtained materials. BaTiO3-CoFe2O4 nanocomposites with up to 20% CoFe2O4 volume fractions were found to display ferrimagnetic properties at room temperature akin to those of CoFe2O4, while preserving a dielectric behavior reminiscent of BaTiO3. Preliminary results describing the spin coating of BaTiO3 and BaTiO3-CoFe2O4 nanocomposites as thin films are also reported.

Ferrimagnetic and relaxor ferroelectric properties of R2MnMn(MnTi3)O12 perovskites with R = Nd, Eu, and Gd

A-site columnar-ordered quadruple perovskites R2MnMn(MnTi3)O12 (R = Nd, Eu, Gd) exhibit relaxor-like ferroelectric properties and ferrimagnetic transitions with large moments.

The Properties of xBiFeO3–(1 – x)SrTiO3 (x = 0.2–1.0; Δx = 0.1) Solid Solutions: Mössbauer Studies

The magnetic structure and phase transition in xBiFeO3–(1 – x)SrTiO3 solid solutions, where x is from 0.2 to 1.0 with a step of 0.1, are studied systematically with Mossbauer spectroscopy. The multiferroic BiFeO3 was modified via incorporation of a perovskite SrTiO3, and xBiFeO3–(1 – x)SrTiO3 solid solutions that possess both ferrimagnetic and ferroelectric properties at room temperature were prepared. X-ray diffraction data indicate that there are no any additional phases in the xBiFeO3–(1 – x)SrTiO3 systems, whereas Mossbauer data show that there is a mullinite (Bi2Fe4O9), when amount x of SrTiO3 in the solid solution is from 1.0 to 0.8. The Mossbauer spectra of the xBiFeO3–(1 – x)SrTiO3 system at room temperature show that when amount of BiFeO3 in the solid solution decreases, the magnetic hyperfine field values decrease as well and the widths of absorption line increase due to the weakening of the magnetic exchange interaction. The Mossbauer spectra of the systems with x < 0.5 indicate that the solid solution is paramagnetic. A relationship between the intensity of Zeeman lines and an amount of BiFeO3 in BiFeO3–(1 – x)SrTiO3 solid solution showed that the transition of this system to the paramagnetic state proceeded at room temperature, when x value was 0.4 (between x = 0.3 and 0.5).

Nuclear Magnetic Relaxation Time near the Compensation Temperature in a Ferrimagnetic Insulator

The nuclear magnetic relaxation time $T_1$ in ferrimagnetic insulators is calculated by a Raman process of hyperfine interaction with a meanfield approximation. It is found that the 1/$T_1$ on one site rapidly increases near the compensation temperature $T_0$, whereas that on another site does not increase up to Curie temperature $T_c$. This is due to that the band width of soft magnon becomes comparable to $T_0$. The increasing behavior of 1/$T_1$ below $T_c$ is found also in another type ferrimagnet, which shows hump structure in the temperature dependence of magnetization instead of compensation. Also in this case, we find the rapid increase of 1/$T_1$ below $T_c$, even though the magnetization does not show the compensation. Such a coexistence of soft and hard magnons will lead to remarkable properties of ferrimagnet.

Enhancement of Mn-doped magnetite by mesoporous silica for technological application

Mn0.6Fe2.4O4 was synthesized by the co-precipitation method. A simple method was developed for preparing Mn0.6Fe2.4O4@SiO2 nanocomposite via few steps. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) images, BET surface area measurements were used to characterize the physical structures of the investigated samples. The crystallite size of the nanocomposite is greater than that of the parent sample. The dielectric constant (e/) of the Mn0.6Fe2.4O4 is greater than that of the sample Mn0.6Fe2.4O4@SiO2. The investigated samples have a semiconductor-like behavior with two different conduction mechanisms. M-H loops of the samples show ferrimagnetic properties. Mesoporous silica increased the coercive field and decreases the values of both Ms and Mr of Mn0.6Fe2.4O4. Mn0.6Fe2.4O4@SiO2 nanocomposite exhibits higher removal efficiency than Mn0.6Fe2.4O3. The maximum removal of the heavy metals is observed for Pb2+ and Cr6+.

Theoretical analysis on O vacancy and cation inversion in NiCo2O4

We have implemented polarized density function theory (DFT) on the transition metal d orbitals to explore the effects of oxygen vacancy and cation inversion on properties of NiCo2O4. The results show that NiCo2O4 has ferrimagnetic half-metallic ground states. Oxygen vacancy introduces additional energy levels in the majority spin band gap, which increases the chance of electron transition. In addition, O vacancy only affects the magnetic moment of the neighbor Oct Ni and Oct Co atoms. Calculations on NiCo2O4 with cation inversion confirms that coordinated sites of metal ions affect their spin state and valence, which further influence the conductivity and ferrimagnetic properties. The valence information of metal ions in NiCo2O4 was given. And the increased electron states in top of valence band make great contributions to p-type conductivity of NiCo2O4.