Ferrimagnetic Phase Research Articles

Magnetization reversal driven by electron localization-delocalization crossover in the inverse spinel Co2VO4

Neutron diffraction, magnetization, and muon spin relaxation measurements, supplemented by density functional theory (DFT) calculations are employed to unravel temperature-driven magnetization reversal in inverse spinel ${\mathrm{Co}}_{2}{\mathrm{VO}}_{4}$. All measurements show a second-order magnetic phase transition at ${T}_{\mathrm{C}}=168\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ to a collinear ferrimagnetic phase. Neutron diffraction measurements reveal two antiparallel ferromagnetic (FM) sublattices, belonging to magnetic ions on two distinct crystal lattice sites, where the relative balance between the two sublattices determine the net FM moment in the unit cell. As the evolution of the ordered moment with temperature differs between the two sublattices, the net magnetic moment reaches a maximum at ${T}_{\mathrm{NC}}=138\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ and reverses its sign at ${T}_{\mathrm{MR}}=65\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. The DFT results suggest that the underlying microscopic mechanism for the reversal is a delocalization of the unfilled $3d$-shell electrons on one sublattice just below ${T}_{\mathrm{C}}$, followed by a gradual localization as the temperature is lowered. This delocalized-localized crossover is supported by muon spectroscopy results, as strong ${T}_{1}$ relaxation observed below ${T}_{\mathrm{C}}$ indicates fluctuating internal fields.

A combined study of magnetic, granulometric and geochemical properties from lacustrine sediment in the arid Central Asia: Implications for paleoenvironmental variations

Lacustrine sediments in areas of arid Central Asia are sensitive records for paleoenvironmental variations largely associated with the westerlies, targeting the possible transitional linkage between the North Atlantic climate zone and monsoonal eastern Asia. An extensive cognition of paleoenvironmental proxies is a precondition for better deciphering and refining the paleoenvironmental setting. In this study, a combined analysis of magnetic, granulometric and geochemical properties was carried out on lacustrine sediment from the northeastern part of the Yili Basin in northwest China. Results show that magnetic properties within different sedimentary layers may largely respond to the mineral preservation in relation to hydrodynamic inputs and post-depositional alteration. Magnetic concentration was potentially dominated by the input flux of detrital materials, but the depletion of magnetic concentration in the middle part of the section probably arises from post-depositional alteration of the ferrimagnetic phases in sediment with high organic content. This depletion also leads to an enhancement of the fine-grained magnetic phases. Based on the analysis of magnetic and other non-magnetic proxies, three phases of paleoenvironmental variation were identified with regard to the changes in hydrodynamic conditions. Strong hydrodynamic conditions dominated in the lower part of the sections, while there were weaker conditions operated in the middle part of the section, which also underwent post-depositional processes. The upper part of the section experienced undulating hydrodynamic conditions. In addition, this study proposed that the χARM/SIRM ratio possibly has the potential to indicate paleoenvironmental changes and emphasized that the sole usage of magnetic data alone would not deliver comprehensive information of paleoenvironmental evolution. Furthermore, this study also suggests that interdisciplinary study of magnetic transformation in lacustrine sediments is still essential in the future.

Ultrafast probe of magnetization dynamics in multiferroic CoCr2O4 and Co0.975Ge0.025Cr2O4

We report on element-resolved ultrafast magnetization dynamics in multiferroic ${\mathrm{CoCr}}_{2}{\mathrm{O}}_{4}$ and ${\mathrm{Co}}_{0.975}{\mathrm{Ge}}_{0.025}{\mathrm{Cr}}_{2}{\mathrm{O}}_{4}$ after optical excitation above the electronic band gap. We observe demagnetization dynamics in the range of several picoseconds, up to two orders of magnitude faster than previously reported demagnetization in other ferrimagnetic insulators. Moreover, we find that the dynamics of the two magnetic ions differ significantly just below the Curie point. The dynamics of the low-temperature multiferroic phase are almost two times slower than those in the ferrimagnetic phase. This suggests that the additional magnetic cycloidal component, which is coupled to electric polarization at low temperatures, might influence the ultrafast magnetization dynamics.

Spin-polarized imaging of strongly interacting fermions in the ferrimagnetic state of the Weyl candidate CeBi

CeBi has an intricate magnetic phase diagram whose fully polarized state has recently been suggested as a Weyl semimetal, though the role of $f$ states in promoting strong interactions has remained elusive. Here we focus on the less-studied but also time-reversal symmetry-breaking ferrimagnetic phase of CeBi, where our density functional theory (DFT) calculations predict additional Weyl nodes near the Fermi level ${E}_{F}$. We use spin-polarized scanning tunneling microscopy and spectroscopy to image the surface ferrimagnetic order on the itinerant Bi $p$ states, indicating their orbital hybridization with localized Ce $f$ states. We observe suppression of this spin-polarized signature at ${E}_{F}$, coincident with a Fano line shape in the conductance spectra, suggesting the Bi $p$ states partially Kondo screen the $f$ magnetic moments, and this $p\ensuremath{-}f$ hybridization causes strong Fermi-level band renormalization. The $p$-band flattening is supported by our quasiparticle interference measurements, which also show band splitting in agreement with DFT, painting a consistent picture of a strongly interacting magnetic Weyl semimetal.

Magnetic interaction between soft and hard ferrimagnetic phases in BaFe12O19 + CuFe2O4 composite

Magnetic behavior of (with x = 1, 2, and 4) has been explored. These composites were prepared by the standard sol-gel route. X-ray diffraction, Field Emission Scanning Electron Microscopy, and Transmission Electron Microscopy techniques were employed to characterize the composites. The magnetic interaction between and particles in the composite has been studied by recording the M–H hysteresis loops by employing the Vibrating Sample Magnetometer technique. The role of copper ferrite in the composite has been explored. It is interesting to note that the (i.e. x =1) composite shows the maximum magnetic parameters (M s , H c , and (BH) max) among all the composite samples under study. Hence, this composition has been investigated extensively by annealing at different temperatures to optimize its magnetic properties. The + composite annealed at 1000 oC exhibits the maximum energy product (BH) max and saturation magnetization (M s ). The magnetic interaction between two different magnetic phases in the composite has been explored by using the Henkel plot study with the help of isothermal remanent magnetization (IRM) and direct current demagnetization (DCD) M–H curves. The exchange coupling between soft and hard magnetic phases in the composite is also examined by the derivative of magnetization with the magnetic field.

First Order Transitions Between the Gapped Spin-Liquid and Ferrimagnetic Phases in \((1/2,1/2,1)\) Mixed Diamond Chains with Bond Alternation

The ground-state phases of mixed diamond chains with bond alternation $\delta$, and ($S, \tau^{(1)}, \tau^{(2)})=(1/2,1/2,1)$, where $S$ is the magnitude of vertex spins, and $\tau^{(1)}$ and $\tau^{(2)}$ are those of apical spins, are investigated. The two apical spins in each unit cell are connected by an exchange coupling $\lambda$. The exchange couplings between the apical spins and the vertex spins take the values $1+\delta$ and $1-\delta$ alternatingly. This model has an infinite number of local conservation laws. For large $\lambda$ and $\delta \neq 0$, the ground state is equivalent to that of the spin $1/2$ chain with bond alternation. Hence, the ground state is a gapped spin liquid. This energy gap vanishes for $\delta=0$. With the decrease of $\lambda$, the ground state undergoes a transition at $\lambda=\lambda_{\rm c0}(\delta)$ to a series of ferrimagnetic phases with a spontaneous magnetization $m_{\rm sp}=1/p$ per unit cell where $p$ is a positive integer. It is found that this transition is a first order transition for $\delta\neq 0$ with a discontinuous change in $m_{\rm sp}$, while no discontinuity is found for $\delta=0$. The critical behaviors of $m_{\rm sp}$ and $\lambda_{\rm c0}(\delta)$ around the critical point $(\delta,\lambda) =(0, \lambda_{\rm c0}(\delta))$ are also discussed analytically.

Large Magnetic-Field-Induced Strain at the Spin-Reorientation Transition in A-Site Ordered Spinel Oxide LiFeCr4O8

Sintered samples of a spinel oxide LiFeCr4O8, where Cr3+ and Fe3+ ions have localized moments, were found to show a large magnetic-field-induced volume increase approaching 500 ppm by applying a magnetic field of 9 T. This large volume increase appeared only at around 30 K. At 30 K, a spin-reorientation transition from ferrimagnetic to conical order occurs, giving rise to this large volume increase. The coexistence of ferrimagnetic and conical phases at this transition was found to be important, suggesting that such a large magnetic-field-induced volume change can be realized at various magnetic transitions in localized magnets with strong spin-lattice coupling.

A -site Mn2+ tuned magnetism and electrical transport properties in the transition-metal-only perovskite oxide MnCu3Mn4O12

An $A{A}_{3}^{\ensuremath{'}}{B}_{4}{\mathrm{O}}_{12}$-type transition-metal-only quadruple perovskite oxide $\mathrm{Mn}{\mathrm{Cu}}_{3}{\mathrm{Mn}}_{4}{\mathrm{O}}_{12}$ was prepared by high-pressure and high-temperature methods. The compound has a cubic $Im$-3 symmetry with charge distribution of ${\mathrm{Mn}}^{2+}{\mathrm{Cu}}_{3}^{2+}{\mathrm{Mn}}_{4}^{4+}{\mathrm{O}}_{12}$. A long-range ferrimagnetic phase transition caused by ${\mathrm{Cu}}^{2+}(\ensuremath{\uparrow}){\mathrm{Mn}}^{4+}(\ensuremath{\downarrow})$ spin interaction is found to occur at a Curie temperature ${T}_{\mathrm{C}}\ensuremath{\approx}365\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ . Different from the isostructural compound $\mathrm{Ca}{\mathrm{Cu}}_{3}{\mathrm{Mn}}_{4}{\mathrm{O}}_{12}$, the susceptibility of $\mathrm{Mn}{\mathrm{Cu}}_{3}{\mathrm{Mn}}_{4}{\mathrm{O}}_{12}$ experiences a second anomaly \ensuremath{\sim}200 K due to the effects of $A$-site ${\mathrm{Mn}}^{2+}$ spin ordering. Moreover, the $A$-site ${\mathrm{Mn}}^{2+}$ spins also considerably decrease the magnitude of resistivity. Theoretical calculations reveal that the $A$-site Mn $3d$ orbitals locate near the Fermi level and hybridize with the Cu $3d$ and O $2p$ orbitals, playing a crucial role on the magnetic and electrical transport properties of $\mathrm{Mn}{\mathrm{Cu}}_{3}{\mathrm{Mn}}_{4}{\mathrm{O}}_{12}$. In this paper, we provide an interesting example using $A$-site magnetic ions to significantly tune the physical properties in $A{A}_{3}^{\ensuremath{'}}{B}_{4}{\mathrm{O}}_{12}$-type quadruple perovskite oxides.

Epitaxial growth and magnetic characterization of EuSe thin films with various crystalline orientations

We report different growth modes and corresponding magnetic properties of thin EuSe films grown by molecular beam epitaxy on BaF2, Pb1−xEuxSe, GaAs, and Bi2Se3 substrates. We show that EuSe grows predominantly in the (001) orientation on GaAs(111) and Bi2Se3, but along the (111) crystallographic direction on BaF2 (111) and Pb1−xEuxSe (111). High resolution transmission electron microscopy measurements reveal a sharp and highly crystalline interface for both (001) and (111) EuSe films. In agreement with previous studies, ordered magnetic phases include antiferromagnetic, ferrimagnetic, and ferromagnetic phases. In contrast to previous studies, we found a strong hysteresis of the antiferromagnetic–ferrimagnetic transition. The ability to grow epitaxial films of EuSe on Bi2Se3 and of Bi2Se3 on EuSe enables further investigation of interfacial exchange interactions between various phases of an insulating metamagnetic material and a topological insulator.

Emergence of exchange bias and giant coercive field enhancement by internal magnetic frustration in La0.67Sr0.33MnO3 thin films

We have studied the influence of controlled defects on the magnetic properties of La0.67Sr0.33MnO3 (LSMO) thin films. We used 100 nm thick epitaxial LSMO films, which were grown on SrTiO3 substrates and introduced stoichiometry changes and defects using oxygen ion irradiation through nanoporous alumina masks. Oxygen irradiation through the mask creates cascades of defects in spatially-modulated regions in the plane of the LSMO film. The magnetic properties of the samples were compared before and after the irradiation. We have found that irradiation reduces the ferromagnetic ordering temperature, decreases the total magnetization, enhances the coercivity, and induces exchange bias below 50 K. The coercivity enhancement is dramatically higher below 50 K and can be associated with exchange bias. These results can be explained by the formation of Mn-rich antiferromagnetic or ferrimagnetic phases within the bombarded regions that are exchange coupled to the non-irradiated - ferromagnetic host.

Structural, microstructural and temperature dependent magnetic properties of Mg–Ni doped CoCr2O4 ceramics

In the present work, [Co(1-(x + y)) MgxNiy][Cr2]O4 (CMNCr)(where, x = y = 0, 0.10, 0.20) NPs are examine in detail by using experimental results. Solution combustion method is adopted to prepare the CMNCr NPs. Experimental results were studied to understand structure (using XRD), microstructure (using SEM) and magnetic behaviour (using SQUID). The structural analysis was confirmed a single-phase spinel cubic structure with singular structural distortions associated with Mg–Ni doping and the generation of metal vacancies. SEM micrographs of all samples reveal their highly porous nature. EDS was utilized to examine the elemental analysis of the samples. The formation of spinel cubic structure without impurity were also confirmed by Fourier-transform infrared (FTIR) spectroscopy and the same tool is used to investigate the absorption bands related to the A-site and B-site. For all samples, paramagnetic phase to ferrimagnetic phase transition observed at TC and conical spiral spin order transition observed at TS. The curie temperature is found to be 98 K, 89 K, and 85 K for [Co][Cr2]O4, [Co0.8 Mg0.1Ni0.1][Cr2]O4 and [Co0.6 Mg0.2Ni0.2][Cr2]O4 samples, respectively. The spiral transition temperature is found to be 26 K, 14 K and 8 K for [Co][Cr2]O4, [Co0.8 Mg0.1Ni0.1][Cr2]O4 and [Co0.6 Mg0.2Ni0.2][Cr2]O4 samples, respectively. All of the samples exhibit paramagnetic behaviour above TC. The negative magnetization effect were observed in [Co0.6 Mg0.2Ni0.2][Cr2]O4 NPs. 20% of Mg and 20% of Ni substitution to Co site in [Co][Cr2]O4 leads to the evident magnetization reversal at the compensation temperature with an applied magnetic field of 100 Oe. The M − H loop at 10 K exhibits large coercivity due to the spiral spin ordering. This phenomenon of negative magnetization in the material results in a stable state of magnetization in the material, which has significant applications in the field of magnetic storage devices.

Dynamic multicritical phase diagrams of the mixed spin (2, 5/2) Blume-Emery-Griffiths model with repulsive biquadratic coupling

We investigated the dynamic phase transitions (DPTs) in the mixed spin (2, 5/2) Blume-Emery Griffiths model with repulsive biquadratic interaction in the presence of a time-varying magnetic field. We used the path probability method to obtain the set of the dynamic equations. We numerically solved these dynamic equations to characterize the nature of first- and second-order phase transitions and to find the DPT temperatures as well as obtain the phases in the system. We constructed the dynamic phase diagrams (DPDs) in reduced temperature and amplitude of oscillating magnetic field plane. We observed that the DPDs display richer, complex and more topological various type of phase diagrams. In particular, DPDs exhibit the disordered phase, antiquadrupolar or staggered phase, six different ferrimagnetic phases, three different nonmagnetic phases, and numerous mixed phases. DPDs also display two dynamic tricritical points for only smaller values of crystal-field interactions, multiple critical end and double critical end points, one zero-temperature critical point, one inverse critical end point, and a quadruple point depending on interaction parameters. The system always shows the reentrant behaviors for the higher values of magnetic field amplitude, but it does not exhibit the dynamic tricritical behavior for higher values of crystal-field parameter.

Негейзенберговский ферримагентик с одноионной анизотропией

We have investigated the effect of single-ion anisotropy of the "easy plane" type on the phase states of a ferrimagnet with S = 1 and σ=1/2 sublattices and non-Heisenberg (bilinear and biquadratic in spins) exchange interaction for the sublattice with S = 1. It is shown that taking into account both the non-Heisenberg exchange interaction and the single-ion anisotropy of the sublattice with S = 1 leads to the realization of a phase with vector order parameters (ferrimagnetic phase) and a phase characterized by both vector and tensor order parameters (quadrupole-ferrimagnetic). It is shown that taking into account single-ion anisotropy changes the type of phase transition in comparison with an isotropic non-Heisenberg ferrimagnet. A phase diagram is constructed, and the condition for the compensation of the sublattice spins is determined.

Non-Heisenberg ferrimagnet with single-ion anisotropy

We have investigated the effect of single-ion anisotropy of the "easy plane" type on the phase states of a ferrimagnet with S=1 and sigma=1/2 sublattices and non-Heisenberg (bilinear and biquadratic in spins) exchange interaction for the sublattice with S=1. It is shown that taking into account both the non-Heisenberg exchange interaction and the single-ion anisotropy of the sublattice with S=1 leads to the realization of a phase with vector order parameters (ferrimagnetic phase) and a phase characterized by both vector and tensor order parameters (quadrupole-ferrimagnetic). It is shown that taking into account single-ion anisotropy changes the type of phase transition in comparison with an isotropic non-Heisenberg ferrimagnet. A phase diagram is constructed, and the condition for the compensation of the sublattice spins is determined. Keywords: ferrimagnet, biquadratic exchange interaction, single-ion anisotropy "easy plane", quadrupole-ferrimagnetic phase, phase transition.

Tuning the magnetic properties of NiPS3 through organic-ion intercalation.

Atomically thin van der Waals magnetic crystals are characterized by tunable magnetic properties related to their low dimensionality. While electrostatic gating has been used to tailor their magnetic response, chemical approaches like intercalation remain largely unexplored. Here, we demonstrate the manipulation of the magnetism in the van der Waals antiferromagnet NiPS3 through the intercalation of different organic cations, inserted using an engineered two-step process. First, the electrochemical intercalation of tetrabutylammonium cations (TBA+) results in a ferrimagnetic hybrid compound displaying a transition temperature of 78 K, and characterized by a hysteretic behavior with finite remanence and coercivity. Then, TBA+ cations are replaced by cobaltocenium via an ion-exchange process, yielding a ferrimagnetic phase with higher transition temperature (98 K) and higher remanent magnetization. Importantly, we demonstrate that the intercalation and cation exchange processes can be carried out in bulk crystals and few-layer flakes, opening the way to the integration of intercalated magnetic materials in devices.

Critical Behavior at Paramagnetic to Ferrimagnetic Phase Transition in A-Site Ordered Perovskite Cacu3cr2nb2o12

Critical Behavior at Paramagnetic to Ferrimagnetic Phase Transition in A-Site Ordered Perovskite Cacu3cr2nb2o12

Effect of a uniform random external magnetic field with spatiotemporal variation on compensation in Ising spin-1/2 trilayered square ferrimagnets.

Trilayered spin-1/2 Ising ferrimagnets are interesting thin systems for compensation phenomenon. In this work, a Metropolis Monte Carlo study is performed on the magnetic and thermodynamic response of such a system on square Bravais lattice, driven by uniform random external magnetic field with spatiotemporal variations. In two distinct configurations, the surface layers are made up of A and the middle layer is made up of B atoms in an ABA-type stacking while in AAB-type stacking, the top layer and the middle layer is made up of A atoms while the bottom layer is made up of B atoms. The magnetic coupling between the like atoms (A-A and B-B) is ferromagnetic while between the unlike atoms (A-B), it is antiferromagnetic. For the time-dependent external uniform random field, the mean is always set to zero and the standard deviation is varied until spin-field energy is comparable to the dominant cooperative energy of the system. The findings show that the observed compensation and critical points shift and steady-state magnetic behaviors shift among N, L, P, and Q, etc., type of ferrimagnetic behaviors, depending on the strength of external uniform random field. The compensation phenomenon even vanishes after crossing a finite threshold of standard deviation of the magnetic field for particular choices of the other controlling parameters. Thus islands of ferrimagnetic phase without compensation appear within the phase area with compensation of field-free case, in the two-dimensional Hamiltonian parameter space. For both the configurations, the areas of such islands even grow with increasing standard deviation of the external field, σ, obeying a scaling relation of the form: f(σ,A(σ))=σ^{-b}A(σ) with b_{ABA}=1.958±0.122 and b_{AAB}=1.783±0.118.

Ground State, Magnetization Process and Bipartite Quantum Entanglement of a Spin-1/2 Ising-Heisenberg Model on Planar Lattices of Interconnected Trigonal Bipyramids.

The ground state, magnetization scenario and the local bipartite quantum entanglement of a mixed spin- Ising–Heisenberg model in a magnetic field on planar lattices formed by identical corner-sharing bipyramidal plaquettes is examined by combining the exact analytical concept of generalized decoration-iteration mapping transformations with Monte Carlo simulations utilizing the Metropolis algorithm. The ground-state phase diagram of the model involves six different phases, namely, the standard ferrimagnetic phase, fully saturated phase, two unique quantum ferrimagnetic phases, and two macroscopically degenerate quantum ferrimagnetic phases with two chiral degrees of freedom of the Heisenberg triangular clusters. The diversity of ground-state spin arrangement is manifested themselves in seven different magnetization scenarios with one, two or three fractional plateaus whose values are determined by the number of corner-sharing plaquettes. The low-temperature values of the concurrence demonstrate that the bipartite quantum entanglement of the Heisenberg spins in quantum ferrimagnetic phases is field independent, but twice as strong if the Heisenberg spin arrangement is unique as it is two-fold degenerate.

Strain dependence of Berry-phase-induced anomalous Hall effect in the non-collinear antiferromagnet Mn3NiN

The anomalous Hall effect (AHE) has been shown to be present in certain non-collinear antiferromagnets due to their symmetry-breaking magnetic structure, and its magnitude is dependent primarily on the non-zero components of the Berry curvature. In the non-collinear antiferromagnet Mn3NiN, the Berry phase contribution has been predicted to have strong strain dependence, although in practice, direct observation may be obscured by other strain-related influences—for instance, magnetic phase transitions mediated by strain. To unravel the various contributions, we examine the thickness and temperature dependence of the AHE for films grown on the piezoelectric substrate BaTiO3. We observe a systematic reduction in TN due to increased compressive strain as film thickness is reduced and a linear decrease in the AHE magnitude as the films are cooled from their ferrimagnetic phase above TN to their antiferromagnetic phase below. At 190 K, we applied an electric field across a 0.5 mm thick BaTiO3 substrate with a 50 nm thick Mn3NiN film grown on top and we demonstrate that at the coercive field of the piezoelectric substrate, the tensile in-plane strain is estimated to be of the order of 0.15%, producing a 20% change in AHE. Furthermore, we show that this change is, indeed, dominated by the intrinsic strain dependence of the Berry curvature.

Colossal angular magnetoresistance in ferrimagnetic nodal-line semiconductors.

Efficient magnetic control of electronic conduction is at the heart of spintronic functionality for memory and logic applications1,2. Magnets with topological band crossings serve as a good material platform for such control, because their topological band degeneracy can be readily tuned by spin configurations, dramatically modulating electronic conduction3-10. Here we propose that the topological nodal-line degeneracy of spin-polarized bands in magnetic semiconductors induces an extremely large angular response of magnetotransport. Taking a layered ferrimagnet, Mn3Si2Te6, and its derived compounds as a model system, we show that the topological band degeneracy, driven by chiral molecular orbital states, is lifted depending on spin orientation, which leads to a metal-insulator transition in the same ferrimagnetic phase. The resulting variation of angular magnetoresistance with rotating magnetization exceeds a trillion per cent per radian, which we call colossal angular magnetoresistance. Our findings demonstrate that magnetic nodal-line semiconductors are a promising platform for realizing extremely sensitive spin- and orbital-dependent functionalities.