Ferrimagnetic Phase Transition Research Articles

High-pressure synthesis and magnetic characterization of quadruple perovskites SmA′3Co4O12 (A′ = Cu, Mn)

In this study, two novel quadruple perovskite compounds SmA′3Co4O12 (A′ = Cu, Mn) were synthesized using a high-pressure synthesis method. Structural analysis of the perovskites using synchrotron X-ray powder diffraction revealed that both SmCu3Co4O12 and SmMn3Co4O12 have cubic Im3‾ structure. In the temperature range of 2–300 K, SmCu3Co4O12 did not exhibit a magnetic phase transition, whereas SmMn3Co4O12 exhibited a paramagnetic to ferrimagnetic phase transition at ∼90 K. A comparison of structural information, X-ray absorption near edge structure, and magnetic properties revealed that the low-spin state (S = 0) characterizes the spin state of Co3+ when the A′ site is occupied by Cu3+. However, when the A′ site is occupied by Mn3+, the Co3+ spin state is in a high-spin state (S = 2), indicating that a long-range magnetic phase transition occurs owing to the magnetic interaction between the Mn and Co ions.

High-Pressure Synthesis of Semiconducting PbCu3Mn4O12 with Near-Room-Temperature Ferrimagnetic Order.

A transition-metal oxide of PbCu3Mn4O12 was prepared at 1523 K and 10 GPa. An A-site-ordered quadruple perovskite structure with the space group Im3̅ is assigned for this compound. Based on bond-valence-sum calculations and X-ray absorption spectroscopy, the charge combination is determined to be PbCu32+Mn44+O12. Due to Cu2+(↑)-Mn4+(↓) antiferromagnetic coupling, a near-room-temperature ferrimagnetic phase transition is observed at approximately 287 K. PbCu3Mn4O12 exhibits a semiconducting electric transport property with the energy band gap Eg ≈ 0.2 eV. In addition, considerable low-field magnetoresistance effects are observed at lower temperatures. This study provides an intrinsic near-room-temperature ferrimagnetic semiconductor that exhibits potential applications in next-generation spintronic devices.

Study of structural, X-ray photoelectron spectroscopy, Raman and temperature-dependent magnetic studies of NiFe2O4/CoCr2O4 nanocomposites

In recent years, cobalt chromites/nickel ferrites have been attractive candidates for significant applications as nanomagnets. In the present work, structural, electronic, vibrational and low-temperature magnetic properties of NiFe2O4, CoCr2O4, and NiFe2O4/CoCr2O4 nanocomposites were investigated. Refined XRD patterns and the Raman spectra confirm the formation of the pure crystalline spinel cubic phase. The estimated crystallite size is in the range of 14 - 29 nm. X-ray photoelectron spectroscopy (XPS) confirm the oxidation state of all elements present in the synthesized samples. The studies of the photoemission core level lines prove the cations distribution in the tetrahedral and octahedral sites with the expected valence states. The magnetic studies reveal the S-type hysteresis loops, confirming the ferrimagnetic nature. The remanent and saturation magnetization increase with increasing NiFe2O4 concentration and decrease with increasing temperature. The magnetization also increases with increase of crystallite size. The temperature-dependent magnetization curve of CoCr2O4 shows the ferrimagnetic phase transition at Curie temperature TC = 86 K. The performed density functional theory (DFT) calculations indicate a significant distribution of the density of states over the Fermi level in NiFe2O4/CoCr2O4 composites as compared to bare NiFe2O4 and CoCr2O4 materials, confirming the improved electronic properties. The overall magnetic analysis proved the magnetization enhancement by increasing x concentration.

High temperature magneto-dielectric response and dielectric relaxations in PrIG

A high temperature MD effect has been observed in Pr3Fe5O12 (PrIG) which is a new member of rare earth iron garnets (RIG) family. Research indicates that this material has two dielectric relaxations in the temperature range from 370 K to 565 K and a dielectric anomaly around 580 K. The first dielectric relaxation is attributed to the conduction for the similar activation energy with conduction. The other dielectric relaxation in the higher temperature range originated from the inhomogeneous structure. And, the coupling between the ferrimagnetic phase transition and the dielectric response was observed at 1 kHz 0.35 T 580K.

CaCu3Mn2Te2O12: An Intrinsic Ferrimagnetic Insulator Prepared Under High Pressure.

CaCu3Mn2Te2O12 was synthesized using high-temperature and high-pressure conditions. The compound possesses an A- and B site ordered quadruple perovskite structure in Pn3̅ symmetry with the charge combination of CaCu32+Mn22+Te26+O12. A ferrimagnetic phase transition originating from the antiferromagnetic interaction between A' site Cu2+ and B site Mn2+ ions is found to occur at TC ≈ 100 K. CaCu3Mn2Te2O12 also shows insulating electric conductivity. Optical measurement demonstrates the energy bandgap to be about 1.9 eV, in agreement with the high B site degree of chemical order between Mn2+ and Te6+. The first-principles theoretical calculations confirm the Cu2+(↓)-Mn2+(↑) ferrimagnetic coupling as well as the insulating nature with an up-spin direct bandgap. The current CaCu3Mn2Te2O12 provides an intriguing example of an intrinsic ferrimagnetic insulator with promising applications in advanced spintronic devices.

Ferrimagnetic quantum phase transitions and Weyl-Kondo semimetal in a dimerized organic polymer

We study the ferrimagnetic quantum phase transitions (QPTs) and thermodynamics of a dimerized organic polymer, which is described as a periodic Anderson-like model using Green’s function theory. In the absence of magnetic field, it is shown that the Kondo coupling could destroy the Dirac semimetal and induce spin splitting, and the dimerization could open up an energy gap. In a magnetic field, the ferrimagnetic and ferromagnetic insulators as well as Weyl-Kondo semimetal are unveiled. The mechanism of Kondo-singlet competition with dimer-singlet is unveiled to account for the 1/3 magnetization plateau. The field induces second and first order QPTs in the small and large hybridization limit, which is demonstrated by the field scaling of Grüneisen ratio and temperature scaling of specific heat at low temperatures, providing novel thermodynamic means to diagnose the order of QPTs.

Broadband magnetic and dielectric properties of U-type hexaferrite Sr4CoZnFe36O60

Sr4CoZnFe36O60 ceramics with U-type hexaferrite crystal structure were for the first time prepared and their structural, dielectric, magnetic and magnetoelectric properties were characterized. Broadband dielectric spectra (1 Hz −1 GHz) showed giant permittivity due to two Maxwell-Wagner dielectric relaxations whose frequencies follow the Arrhenius law. These relaxations are caused by inhomogeneous conductivity in the ceramic grains and their boundaries. Temperature and magnetic field dependences of magnetization revealed ferrimagnetic phase transition at Tc1 = 635 K and other two magnetic phase transitions at Tc2 = 305 K and Tc3 = 145 K. Magnetoelectric measurement at 10 K revealed only small polarization 35 nC/m2 which has probably extrinsic origin, so the sample is probably not multiferroic. The observed magnetocapacitance effect (-0.8 %) was attributed to the magnetoresistance (-4 %) caused by non-homogeneous conductivity of the ceramics. High-frequency magnetic permeability measured up to 1.8 GHz evidences the Curie-Weiss behavior above Tc2 and Tc3 and two magnetic field-dependent excitations which exhibit anomalies at magnetic phase transitions. We attributed these excitations to the magnetic domain wall dynamics.

High-pressure synthesis and magnetic properties of a Fe/Ru disordered quadruple perovskite CaCu3Fe2Ru2O12

A new quadruple perovskite oxide CaCu3Fe2Ru2O12 was synthesized at 10 GPa and 1400 K. The compound crystallizes into an AA′3B4O12-type perovskite structure with space group Im3¯, where the Ca and Cu ions are 1: 3 ordered at A sites, whereas Fe and Ru ions are disordered at B sites. X-ray photoelectron spectroscopy measurement reveals the charge state formation of CaCu2+3Fe3+2Ru5+2O12. Magnetic measurement shows that ferrimagnetic phase transition occurs at TC ∼348 K. Meanwhile, in a high applied magnetic field, a rapid decrease of zero-field-cooled magnetization MZFC occurs at low temperatures (TH), which may be due to spin-reorientation transition. When the applied pressure increases, TC moves to lower temperatures implying that ferrimagnetic exchange interaction becomes weak, while TH is almost unchanged. Electrical transport measurement shows that the intrinsic electrical behavior is metallic, which is consistent with the specific heat result.

Mixed Spin Ising Ferrimagnetic System in the Oguchi Approximation

It has been investigated an Ising ferrimagnet with mixed spin-2 and spin-5/2 and various crystal field parameters on a body-centered cubic lattice. In this research paper, ferrimagnetic compensation temperatures and phase transitions to clarify the characteristic features, in a series of molecular-based magnets AFeIIFeIII(C2O4)3[A=N(n-CnH2n+1)4, n=3-5] are examined in the Oguchi approximation (OA). The spin crystal domain dependence of compensation behavior acting on ions contain the Oguchi lattice, is mainly studied. It is discovered, specifically, that magnetic anisotropies in the disordered for the two sublattices of the model depend on the negative values of the crystal fields to produce a characteristic ferrimagnetic behavior. For DA/|J|=-1.5 and DB/|J|=-5.5, there are two compensation points are induced at an ordered phase(2,-1.5).

Tunable magnetic and electronic transport properties of Co1+xV2-xO4

Here we present a study on the electronic and magnetic properties of the members of Co1+xV2-xO4 series. The solid-state reaction method was used to grow the polycrystalline samples. Using the localised electron relationship and the various hopping transport regimes, we analyse the electronic transport outcomes. Also, the results of magnetic measurements reveal the ferrimagnetic phase transition and non-collinear spin configuration of these vanadate samples. Additionally, our work illustrates the variation of electronic and magnetic properties with the Co-concentration values.

The structure, magnetic and dielectric properties of the CaBaCo4-xNixO7 (0 ≤ x ≤ 0.1) compounds

We report the structure, magnetic and dielectric behaviors of the polar magnet CaBaCo4-xNixO7 (0 ≤ x ≤ 0.1). The Rietveld refinements results for polycrystalline samples shows that the orthorhombic distortion gradually decreases with the increase of Ni2+ content. Different from the undoped sample, two antiferromagnetic phases and a ferrimagnetic phase can be observed in M-T curves for Ni-doped samples. For x = 0.06, the antiferromagnetic phase around 79K competes with another antiferromagnetic phase that appears around 62K, giving a magnetic plateau between 62K and 79K. With increasing Ni-doping, the ferrimagnetic phase transition peak moves to lower temperature and it fades gradually, while the antiferromagnetic phase transition peak around 79K shifts to higher temperature. The magnetization behaviors could be attributed to the enhanced antiferromagnetic interactions and the reorientation of the adjacent spins of cobalt ions due to the introduction of Ni2+ doping. As a result, the Ni-doped samples present stronger magnetoelectric coupling than the undoped sample, as well as an enhanced polarization.

Critical behavior at paramagnetic to ferrimagnetic phase transition in A-site ordered perovskite CaCu3Cr2Nb2O12

A new perovskite-type oxide, CaCu3Cr2Nb2O12, has been synthesized at 10 GPa and 1100 °C. The compound crystallizes in space group Im3¯ with 1:3 ordered Ca and Cu cations at the A sites and disordered Cr and Nb cations at the octahedral B sites. CaCu3Cr2Nb2O12 exhibits a paramagnetic–ferrimagnetic transition at around 192.3 K and the Arrott plots manifest this transition is a second-order transition. We investigate the critical behavior of CaCu3Cr2Nb2O12 using the modified Arrott plots, Kouvel–Fisher plot, and the scale theory. The estimated critical exponents β, γ and δ, which yield β = 0.465 ± 0.006, γ = 1.312 ± 0.019 and δ = 3.833 ± 0.019 with TC = 197 K, fall within the predicted values from the mean-field model and three-dimensional Heisenberg model. The renormalization group analysis suggests that the exchange interaction decays as J(r)∼ r−4.871, indicating the magnetic interactions may be long-range coupling in CaCu3Cr2Nb2O12.

Spin reorientation in CoV2O4 thin film: A first principles study

Spinel vanadates (AV2O4) are a class of materials where an interesting interplay between spin and orbital degrees of freedom on a frustrated lattice is manifested in the multiple structural and magnetic phase transitions. CoV2O4 is unique among the spinel vanadates as it shows no or very weak cubic to tetragonal structural phase transition but two magnetic (paramagnetic to collinear ferrimagnetic and collinear to noncollinear ferrimagnetic) phase transitions at lower temperatures in its bulk form. In a recent experiment (Thompson et al., Phys. Rev. Mater. 2 (2018) 104411), an epitaxial thin film of CoV2O4 grown on the SrTiO3 (001) substrate, is observed to have an orthorhombic structural phase accompanied by a noncollinear magnetic state where the spin moments of Co and V are reoriented from [001] (seen in the bulk form) to the [110] direction. In this work, we have explored the mechanism behind this complex spin-reorientation and noncollinear magnetic ground state by investigating the electronic structure, magnetic, and structural properties of CoV2O4 in its orthorhombic phase and compared with the corresponding properties of the cubic phase using the first principles density functional theory. Our GGA+U+SO calculations on orthorhombic CoV2O4 reveal that spin moments prefer to lie in the ab-plane with the crystallographic b-direction being the preferred direction in the collinear ferrimagnetic state where it has a larger band gap and orbital moment (of V) as compared to the cases with spin moments aligned parallel to a and c-directions. We further observe competing magnetic exchange interaction values in orthorhombic phase when the spins lie in the ab-plane giving rise to more frustration and hence more canting in the non-collinear magnetic ground stateas compared to the cubic phase, consistent with experiment. With the help of source-free exchange–correlation (XC) functional we were able to capture the non-collinear magnetic ground state and the spin-reorientation in this system. We also discussed the possible orbital ordering in the orthorhombic phase of CoV2O4.

Differences of the temperatures of ferroelectric and magnetic phase transitions of perovskites

Binary and ternary AB′0.5 B″0.5O3 oxides with a complex perovskite structure, possessing the consecutive ferroelectric or antiferroelectric phase transitions at T C and ferromagnetic, antiferromagnetic, or ferrimagnetic phase transitions at T N, are considered together with classical ferroelectrics and antiferroelectrics. The common correlations between these temperatures, their differences T С-T N and interatomic bond A-O (δ AO) or B-O (δ BO) strains are revealed. Some common correlations between their temperatures T С, T N, T С-T N differences, and δ AO or δ BO are revealed. It is established that these differences for multiferroics are in common dependences with classical ferroelectrics and antiferroelectrics.

Spin-phonon coupling in ferrimagnet spinel CoMn2O4.

Coupling of material properties provides new fundamental insights and possibilities toward multifunctional devices. The spinel structures display strong coupling between different order parameters, as a consequence, exhibiting many fascinating properties, such as multiferroicity and superconductivity. Here, we have investigated the structural, magnetic, and vibrational properties of mixed-spinel CoMn2O4 stabilized in distorted tetragonal structures as evidenced from x-ray diffraction measurements. Magnetization measurements reveal two ferrimagnetic phase transitions at 185 and 90K. Raman scattering measurements reveal the renormalization of phonon parameters for a few phonon modes at low temperatures, arising from spin-phonon coupling. The obtained value for λS2 is ∼2cm-1. The strength of spin-phonon coupling (λ) is estimated according to the spins involved in the corresponding lattice vibrations and discussed.

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.

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.

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

Anisotropically large anomalous and topological Hall effect in a kagome magnet

Recently, kagome materials have become an engrossing platform to study the interplay among symmetry, magnetism, topology, and electron correlation. The latest works on $R{\mathrm{Mn}}_{6}{\mathrm{Sn}}_{6}$ ($R$ = rare-earth metal) compounds have illustrated that this family could be intriguing to investigate various physical phenomena due to large spin-orbit coupling and strong magnetic ordering. However, combined transport and spectroscopic studies in $R{\mathrm{Mn}}_{6}{\mathrm{Sn}}_{6}$ materials are still limited. Here, we report magnetic, magnetotransport, and angle-resolved photoemission spectroscopy measurements of a kagome magnet ${\mathrm{ErMn}}_{6}{\mathrm{Sn}}_{6}$ that undergoes antiferromagnetic (${T}_{N}=345\phantom{\rule{0.28em}{0ex}}\mathrm{K}$) to ferrimagnetic (${T}_{C}=68\phantom{\rule{0.16em}{0ex}}\mathrm{K}$) phase transitions in the presence of a field. We observe large anomalous and topological Hall effects serving as transport signatures of the nontrivial Berry curvature. The isothermal magnetization exhibits strong anisotropic nature and the topological Hall effect of the compound depends on the critical field of metamagnetic transition. Our spectroscopic results complemented by theoretical calculations show the multiorbital kagome fermiology. This Letter provides new insight into the tunability and interplay of topology and magnetism in a kagome magnet.

Unveiling the shape-selective CoCr2-yScyO4 nanomagnetism

In this study CoCr2-yScyO4 (y = 0, 0.01, 0.02, and 0.03) nanoparticles (NPs) have been synthesized following the solution combustion method and characterized by combining experimental techniques with high-throughput Density Functional Theory calculations. The structural analysis confirmed the crystalline nature with spinel cubic structure exhibiting an average particle size between 7 and 10 nm. The morphological analysis confirmed the exposure of the (220), (311), (400), and (422) planes in agreement with theoretical results based on Wulff Construction. Magnetic analysis indicated the existence of paramagnetic to ferrimagnetic phase transition at the critical temperature (Tc) and a conical spiral spin phase was found at the spiral transition temperature (Ts). In both the cases, the transition temperature was seen to decrease with increase in the Sc content in agreement with the exchange-coupling constants calculated by DFT, where a singular magneto-structural behavior was observed. Theoretical results for shape-oriented magnetic properties indicate the anisotropic spin density distribution and surface exposure, providing a general picture of shape-selective control of nanomagnetism.