Ferrimagnetic Phase Research Articles

Magnetic-glass-like transition induced by kinetic arrest in ferrimagnetic Mn1.975Cr0.025Sb alloy

The magnetic glass state has been proposed and studied in the ferromagnetic (FM) compounds undergoing the first-order FM-antiferromagnetic (AFM) transition. In this work, we have unequivocally demonstrated the occurrence of magnetic-glass-like transition during the field cooling process in the ferrimagnetic (FIM) Mn1.975Cr0.025Sb alloy showing a first-order FIM-AFM transition. The magnetic, resistance and relaxation studies characterize the formation of a nonergodic magnetic glass-like state at low temperature arising from the coexistence of AFM and kinetically arrested FIM phases above a critical applied field. The magnetic field-temperature (μ0H-T) phase diagram based on magnetic and resistance measurements further evidences the generality of onset of glassy behavior in the first-order magnetic transition materials, in which the transition temperature shifts strongly with increasing applied field.

Magnetic enhancement of ferroelectric polarization in a particulate multiferroic composite derived in situ via additive assisted sintering of a pseudo ternary alloy system BiFeO3–PbTiO3–DyFeO3

We report here the synthesis of a self-grown 0–3 particulate multiferroic composite by controlled precipitation of the ferrimagnetic garnet phase using additive (MnO2) assisted sintering of a multi-cation ferroelectric system (Bi, Pb, Dy)(Fe, Ti)O3. The particulate multiferroic composite derived in this manner exhibits a favorable microstructure, wherein, although the volume fraction of the garnet phase is kept low (6%), which helps in retaining the electrical insulating character of the specimen, the number fraction of the garnet grains vis-à-vis the ferroelectric grains is ∼1:1. The composite shows a nearly ∼50% increase in saturation polarization at room temperature under a modest magnetic field of 1 T, suggesting a considerable improvement in ferroelectric domain switching due to the efficient strain transfer from the minority garnet grains to the majority piezoelectric grains.

Preparation of the noncentrosymmetric ferrimagnetic phase La0.9Ba0.1Mn0.96O2.43 by topochemical reduction

Topochemical reduction of La0.9Ba0.1MnO3 with NaH at 225 ​°C yields the brownmillerite phase La0.9Ba0.1MnO2.5. However, reduction with CaH2 at 435 ​°C results in the formation of La0.9Ba0.1Mn0.96O2.43 via the deintercalation of both oxide anions and manganese cations from the parent perovskite phase. Electron and neutron diffraction data reveal La0.9Ba0.1Mn0.96O2.43 adopts a complex noncentrosymmetric structure, described in space group I23, confirmed by SHG measurements. Low-temperature neutron diffraction data reveal La0.9Ba0.1Mn0.96O2.43 adopts an ordered magnetic structure in which all the nearest neighbor interactions are antiferromagnetic. However, the presence of ordered manganese cation-vacancies results in a net ferrimagnetic structure with net saturated moment of 0.157(2) μB per manganese center.

Novel mixed precursor approach to prepare multiferroic nanocomposites with enhanced interfacial coupling

In the present work, we report the preparation of multiferroic PbZr0.52Ti0.48O3 (PZT)/CoFe2O4 (CFO) nanocomposites using a new synthesis technique that can maximize the surface area of contact, and hence, the interfacial coupling between the ferroelectric (PZT) and ferrimagnetic (CFO) phases. The samples have been characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM), and the physical (magnetic and dielectric) properties have been investigated. XRD confirms the presence of the desired PZT and CFO phases in the samples without any undesired secondary phases. We also observe a reduction in the particle size of CFO in the nanocomposites as evidenced by a line broadening of the XRD reflections corresponding to the pure CFO phase. The nanocomposites show hysteresis loops and ferrimagnetic-like behaviors in their M vs H curves at room temperature, even for samples with very low fraction of the CFO phase. The coercivity of the nanocomposites is marginally larger compared to that of pure CFO, which can be due to the change in magnetic anisotropy of the CFO phase due to its reduced particle size in the nanocomposites. Room temperature polarization versus electric field measurements show a significant increase in the coercive field after the incorporation of CFO inside the PZT matrix. This work illustrates a simple, cost-effective synthesis technique that can be used to prepare nanocomposites of functional materials with desired room temperature functionalities and enhanced interfacial coupling between the two phases.

Electronic structure investigation of GdNi using x-ray absorption, magnetic circular dichroism, and hard x-ray photoemission spectroscopy

GdNi is a ferrimagnetic material with a Curie temperature Tc = 69 K which exhibits a large magnetocaloric effect, making it useful for magnetic refrigerator applications. We investigate the electronic structure of GdNi by carrying out x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) at T = 25 K in the ferrimagnetic phase. We analyze the Gd M$_{4,5}$-edge ($3d$ - $4f$) and Ni L$_{2,3}$-edge ($2p$ - $3d$) spectra using atomic multiplet and cluster model calculations, respectively. The atomic multiplet calculation for Gd M$_{4,5}$-edge XAS indicates that Gd is trivalent in GdNi, consistent with localized $4f$ states. On the other hand, a model cluster calculation for Ni L$_{2,3}$-edge XAS shows that Ni is effectively divalent in GdNi and strongly hybridized with nearest neighbour Gd states, resulting in a $d$-electron count of 8.57. The Gd M$_{4,5}$-edge XMCD spectrum is consistent with a ground state configuration of S = 7/2 and L=0. The Ni L$_{2,3}$-edge XMCD results indicate that the antiferromagnetically aligned Ni moments exhibit a small but finite magnetic moment ( $m_{tot}$ $\sim$ 0.12 $\mu_B$ ) with the ratio $m_{o}/m_{s}$ $\sim$ 0.11. Valence band hard x-ray photoemission spectroscopy shows Ni $3d$ features at the Fermi level, confirming a partially filled $3d$ band, while the Gd $4f$ states are at high binding energies away from the Fermi level. The results indicate that the Ni $3d$ band is not fully occupied and contradicts the charge-transfer model for rare-earth based alloys. The obtained electronic parameters indicate that GdNi is a strongly correlated charge transfer metal with the Ni on-site Coulomb energy being much larger than the effective charge-transfer energy between the Ni $3d$ and Gd $4f$ states.

Magnetization plateaus and bipartite entanglement of an exactly solved spin-1/2 Ising-Heisenberg orthogonal-dimer chain

Spin-1/2 orthogonal-dimer chain composed of regularly alternating Ising and Heisenberg dimers is exactly solved in a presence of the magnetic field by the transfer-matrix method. It is shown that the ground-state phase diagram involves in total six different phases. Besides the ferromagnetic phase with fully polarized spins one encounters the singlet antiferromagnetic and modulated antiferromagnetic phases manifested in zero-temperature magnetization curves as zero magnetization plateau, the frustrated ferrimagnetic and singlet ferrimagnetic phases causing existence of an intermediate one-half magnetization plateau, and finally, the intriguing modulated ferrimagnetic phase with a translationally broken symmetry leading to an unconventional one-quarter magnetization plateau. The quantum character of individual ground states is quantified via the concurrence, which measures a strength of the bipartite entanglement within the pure and mixed states of the Heisenberg dimers at zero as well as nonzero temperatures. The parameter region, where the bipartite entanglement may be in contrast to general expectations reinforced upon increasing of temperature and/or magnetic field, is elucidated.

Magnetic properties of Cr-substituted ε-(Fe1-xCrx)2O3 nanoparticles with epsilon structure

ε-Fe2O3 has gained considerable interest due to its intriguing properties and great application potentials. In this work ε-(Fe1−xCrx)2O3 (x = 0, 0.03, 0.075) nanoparticles encapsulated in silica have been successfully prepared by sol–gel chemistry. Synchrotron diffraction confirms that the polar Pna21 structure of ε-Fe2O3 is robust against the substitution of Fe by Cr. The incorporation of chromium is accompanied by a softer magnetic behaviour, and also a gradual decrease in the ferromagnetic signal associated to the super-hard FM2 ferrimagnetic phase. While the Cr substitution has little impact on the low temperature incommensurate transition, it is found that Cr substitution shifts the super-hard and soft ferrimagnetic transitions (respectively, TN2 and TN1) to notably lower temperatures.

Out-of-plane electric polarization in double-fan magnetic phase of Y-type hexaferrite

It has been revealed that a Y-type hexaferrite ${\mathrm{BaSrCo}}_{2}{\mathrm{Fe}}_{11.1}{\mathrm{Al}}_{0.9}{\mathrm{O}}_{22}$ hosts not only an in-plane $({P}_{ab})$ but also an out-of-plane $({P}_{c})$ component of magnetically induced electric polarization in the double-fan magnetic phase. With an increasing in-plane magnetic field, the magnitude of ${P}_{c}$ reaches a maximum at around $2\phantom{\rule{0.28em}{0ex}}\text{T}$ and decreases as approaching the critical field $(3.8\phantom{\rule{0.28em}{0ex}}\text{T})$ of the transition to the collinear ferrimagnetic phase. ${P}_{c}$ has also been verified to show a ${120}^{\ensuremath{\circ}}$-period oscillation as a function of the in-plane magnetic field direction. These results are reproduced by a model combining the inverse Dzyaloshinskii-Moriya interaction and the spin-dependent $pd$ hybridization mechanisms.

Surface Compositional Change of Iron Oxide Porous Nanorods: A Route for Tuning their Magnetic Properties.

The capability of synthesizing specific nanoparticles (NPs) by varying their shape, size and composition in a controlled fashion represents a typical set of engineering tools that tune the NPs magnetic response via their anisotropy. In particular, variations in NP composition mainly affect the magnetocrystalline anisotropy component, while the different magnetic responses of NPs with isotropic (i.e., spherical) or elongated shapes are mainly caused by changes in their shape anisotropy. In this context, we propose a novel route to obtain monodispersed, partially hollow magnetite nanorods (NRs) by colloidal synthesis, in order to exploit their shape anisotropy to increase the related coercivity; we then modify their composition via a cation exchange (CE) approach. The combination of a synthetic and post-synthetic approach on NRs gave rise to dramatic variations in their magnetic features, with the pores causing an initial magnetic hardening that was further enhanced by the post-synthetic introduction of a manganese oxide shell. Indeed, the coupling of the core and shell ferrimagnetic phases led to even harder magnetic NRs.

Exact magnetic properties for classical delta-chains with ferromagnetic and antiferromagnetic interactions in applied magnetic field

We study the thermodynamics of the delta-chain with competing ferro- and antiferromagnetic interactions in an external magnetic field which generalizes the field-free case studied previously. This model plays an important role for the recently synthesized compound Fe$_{10}$Gd$_{10}$ which is nearly quantum critical. The classical version of the model is solved exactly and explicit analytical results for the low-temperature thermodynamics are obtained. The spin-$s$ quantum model is studied using exact diagonalization and finite-temperature Lanzos techniques. Particular attention is focused on the magnetization and the susceptibility. The magnetization of the classical model in the ferromagnetic part of the phase diagram defines the universal scaling function which is valid for the quantum model. The dependence of the susceptibility on the spin quantum number $s$ at the critical point between the ferro- and ferrimagnetic phases is studied and the relation to Fe$_{10}$Gd$_{10}$ is discussed.

Evidence for the coexistence of spin-glass and ferrimagnetic phases in BaFe12O19 due to basal plane freezing.

We present here the results of low-temperature magnetization and X-ray magnetic circular dichroism studies on the single crystals of BaFe12O19 which reveal for the first time the emergence of a spin glass phase, in coexistence with a long-range ordered ferrimagnetic phase, due to the freezing of the basal plane spin component.

Coupled hard-soft spinel ferrite-based core-shell nanoarchitectures: magnetic properties and heating abilities.

Bi-magnetic core–shell spinel ferrite-based nanoparticles with different CoFe2O4 core size, chemical nature of the shell (MnFe2O4 and spinel iron oxide), and shell thickness were prepared using an efficient solvothermal approach to exploit the magnetic coupling between a hard and a soft ferrimagnetic phase for magnetic heat induction. The magnetic behavior, together with morphology, stoichiometry, cation distribution, and spin canting, were investigated to identify the key parameters affecting the heat release. General trends in the heating abilities, as a function of the core size, the nature and the thickness of the shell, were hypothesized based on this systematic fundamental study and confirmed by experiments conducted on the water-based ferrofluids.

Secondary phase strengthened high coercivity in sputtered D022 Mn3−xGa films

Rare-earth-free permanent magnet Mn-Ga alloys have attracted wide interest owing to their large magnetocrystalline anisotropy and high Curie temperature. In this work, we reported a large coercivity of ~22 kOe at room temperature in the Mn3−xGa film, deposited by magnetron sputtering on the Si(0 0 1)/SiO2 substrate. Combined analyses of the x-ray diffraction, magnetization and high-resolution transmission electron microscopy revealed a cubic α-Mn phase coexisting with the main D022 ferrimagnetic phase in the film. It is proved that the mixed structures can refine the magnetic domains, thus enhancing the coercivity in the high temperature annealed sample.

A magnetocaloric study on the series of 3d-metal chromites ACr2O4 where A = Mn, Fe, Co, Ni, Cu and Zn

The 3d-metal chromites ACr2O4 where A is a magnetic ion, show the paramagnetic to ferrimagnetic phase transition at TC while for non-magnetic A-site ion, ACr2O4 show paramagnetic to antiferromagnetic phase transition at TN. In this report, we present the detailed study of magnetic and the magnetocaloric effect (MCE) of the 3d-metal chromites ACr2O4 (where A = Mn, Fe, Co, Ni, Cu, and Zn) near TC and TN. We find the magnitude of MCE (-ΔSM) decreases on decreasing the magnetic moment of A-site ion with an exception for CuCr2O4. Additionally, to know more about the order and nature of phase transition, we have made a scaling analysis of (-ΔSM) for all the chromites across the phase transition temperatures TC and TN.

Anomalous magnetic behavior and complex magnetic structure of proximate LaCrO3—LaFeO3 system

We investigated complex magnetic properties of multifunctional LaCrO3-LaFeO3 system. The magnetic measurements substantiate the presence of competing complex magnetic ordering against temperature, showing paramagnetic to ferrimagnetic transition at ∼300 K, followed by antiferromagnetic (AFM) transition near ∼250 K superimposed on ferrimagnetic phase. The onset of weak ferrimagnetic ordering is attributed to the competing complex interaction between two AFM LaCrO3-LaFeO3 sublattices. The low-temperature AFM ordering is also substantiated by temperature-dependent Raman measurements, where the intensity ratio of 700 cm−1 Raman active mode showed a clear enhancement with lowering the temperature. The non-saturating nature of magnetic moments in LaCrO3-LaFeO6 suggests the predominating AFM ordering in conjunction with ferrimagnetic ordering between 250 K–300 K up to 5 T magnetic field. A complex magnetic structure of LaCrO3-LaFeO3 is constructed, emphasizing the metastable magnetic phase near room temperature and low-temperature antiferromagnetic state.

Weyl nodes and magnetostructural instability in antiperovskite Mn3ZnC

The room temperature ferromagnetic phase of the cubic antiperovskite Mn3ZnC is suggested from first-principles calculation to be a nodal line Weyl semimetal. Features in the electronic structure that are the hallmark of a nodal line Weyl state—a large density of linear band crossings near the Fermi level—can also be interpreted as signatures of a structural and/or magnetic instability. Indeed, it is known that Mn3ZnC undergoes transitions upon cooling from a paramagnetic to a cubic ferromagnetic state under ambient conditions and then further into a noncollinear ferrimagnetic tetragonal phase at a temperature between 250 K and 200 K. The existence of Weyl nodes and their destruction via structural and magnetic ordering are likely to be relevant to a range of magnetostructurally coupled materials.

Revisiting Goodenough-Kanamori rules in a new series of double perovskites LaSr1\u2212xCaxNiReO6

The magnetic ground states in highly ordered double perovskites LaSr1−xCaxNiReO6 (x = 0.0, 0.5, 1.0) are studied in view of the Goodenough-Kanamori rules of superexchange interactions in this paper. In LaSrNiReO6, Ni and Re sublattices are found to exhibit curious magnetic states separately, but no long range magnetic ordering is achieved. The magnetic transition at ~255 K is identified with the independent Re sublattice magnetic ordering. Interestingly, the sublattice interactions are tuned by modifying the Ni-O-Re bond angles through Ca doping. Upon Ca doping, the Ni and Re sublattices start to display a ferrimagnetically ordered state at low temperature. The neutron powder diffraction data reveals long range ferrimagnetic ordering of the Ni and Re magnetic sublattices along the crystallographic b-axis. The transition temperature of the ferrimagnetic phase increases monotonically with increasing Ca concentration.

Tuning the dielectric, ferroelectric and electromechanical properties of Ba0.83Ca0.10Sr0.07TiO3–MnFe2O4 multiferroic composites

We report the successful synthesis of Ba0.83Ca0.10Sr0.07TiO3–MnFe2O4 multiferroic composites showing significant improvement in electromechanical and magnetoelectric properties. All the composite samples have formed a diphasic perovskite-ferrite composite without the presence of any impurity or intermediate phase. The bare as well as composite samples have shown classical dielectric behavior even at higher ferrite substituted samples. The electrical characteristics of composite samples have shown slight deterioration, which is mainly attributed to non-ferroelectric MnFe2O4. However, the composites still exhibit high enough piezoelectric behavior and the modification in the electromechanical response of composites is mainly caused by a change in applied stress with MnFe2O4 addition. The M-H loops of composites have demonstrated a ferrimagnetic behavior with a substantial increase in saturation magnetization on increasing the ferrite concentration. Further, the composites have shown better coupling between the ferroelectric and ferrimagnetic phases, which has resulted in an improved magnetoelectric characteristic. The role of oxygen vacancies on ferroelectric and magnetic properties of prepared composites has been systematically studied.

Interplay between the ferrimagnetic and ferroelectric phases on the large magnetoelectric coupling of xLi0.1Ni0.2Mn0.6Fe2.1O4–(1 − x)Bi0.8Dy0.2FeO3 composites

The multiferroic composites of ferromagnetic Li0.1Ni0.2Mn0.6Fe2.1O4 (LNMFO) and ferroelectric Bi0.8Dy0.2FeO3 (BDFO) with the general formula xLi0.1Ni0.2Mn0.6Fe2.1O4–(1 − x) Bi0.8Dy0.2FeO3 have been prepared by the solid-state reaction route. The XRD analysis has ensured that the composites are composed of a mixture of cubic spinel LNMFO and orthorhombic perovskite BDFO phases. Field Emission Scanning Electron Microscope is used to investigate the surface morphology of the studied compositions. The average grain size of the composites has reduced slightly with the enhancement of ferrite part up to 20% and after that it has increased again. The real part of the initial permeability $$(\mu^{\prime}_{i} )$$ was found to be increasing with ferrite content. The real part of dielectric constant $$(\varepsilon^{\prime})$$ exhibits dispersion at low-frequency region because of Maxwell–Wagner type interfacial polarization. The complex impedance spectroscopy has been used to separate the grain and grain boundary contribution to the total resistance. Existence of the hopping conduction mechanism has been confirmed through the study of electric modulus. The hysteresis loops of the compositions are studied to confirm the response of ferrite part to the applied magnetic field. The magnetoelectric voltage coefficients of the composites have reduced with the ferrite part. The maximum magnetoelectric voltage coefficient is nearly 158 × 103 Vm−1 T−1 for the 0.1LNMFO–0.9BDFO composite, which is about three times of the reported value compared to other composites.

Magnetic and magnetoelectric properties of Y-type Ba0.6Sr1.4Zn2Fe12O22 hexaferrite single crystal

Magnetic and magnetoelectric properties of Y-type hexaferrite single crystal Ba0.6Sr1.4Zn2Fe12O22 were investigated using vibrating sample magnetometer and ferromagnetic resonance (FMR) techniques. It was found that this compound orders magnetically below 400 K and magnetization exhibits a sharp peak at 331 K, which corresponds to magnetic transition from collinear ferrimagnetic phase to a proper screw spin phase with decreasing temperature. Magnetic hysteresis measurements showed stepwise behavior of initial magnetization curve due to sequential metamagnetic transitions with increasing magnetic field. Using novel and sensitive method of electrically modulated FMR it was shown that this Y-type hexaferrite has significant magnetoelectric coupling, which was determined quantitatively at room temperature. Obtained results show that Y-type hexaferrite Ba0.6Sr1.4Zn2Fe12O22 has a rare combination of magnetoelectric coupling and large magnetization at room temperature, which is important for applications in magnetoelectric devices.