Ferrimagnetic Materials Research Articles

Effect of Zn–Cr substitution on the structural, magnetic and electrical properties of magnesium ferrite materials

The ferrite having the general chemical formula Mg1-xZnxFe2-xCrxO4 (x = 0.0, 0.1, 0.3, 0.5 and 0.7) prepared by the solid state technique. The XRD analysis depicted the presence of single phase cubic spinel structure. They showed an increasing trend of lattice parameter with the expansion of the spinel lattice which resulted from the partial incorporation of larger radii. The FT-IR absorption bands are observed at 590 and 430 cm−1 for tetrahedral and octahedral location. These bands are shifting toward 604.7 and 474.15 cm−1 for Zn–Cr substitution due to the change in Me–O covalence. DC electrical resistivity has found to show the highest magnitude 107 Ω cm at x = 0.1, decreases with further increase in content. The hysteresis curves measured at 300 K demonstrate the coercivity and it varies from 146.33 to 9.427 Oe for increasing the content which confirms decreasing the grain size as well as soft ferrimagnetic material.

Unidirectional-propagating surface magnetoplasmon based on remanence and its application for subwavelength isolators

Ferrimagnetic material with remanence holds the potential to realize unidirectional propagation of the electromagnetic field by taking advantage of magnetoplasmon in the subwavelength regime. Here, we theoretically investigate magnetoplasmons in a layered structure consisting of a dielectric sandwiched by two magnetic materials with anti-parallel remanent magnetization directions, which shows a complete unidirectional propagating region for both even and odd symmetry modes when the thickness of the dielectric is smaller than a certain value. Additionally, the even symmetry mode supported by such a one-way waveguide can be effectively, with low insertion loss, excited by the fundamental transverse-electric mode of a traditional metal slab waveguide. Relying on low insertion loss and a one-way propagation feature, we propose a broadband and subwavelength isolator working at the microwave region. Our results demonstrate that remanence based magnetoplasmons provide a promising way to realize devices below the diffraction limit with new functionalities.

Ferrimagnetism and ferromagnetism behavior in (C, Mn) co-doped SnO2 for microwave and spintronic: Ab initio investigation

Abstract In this paper, the challenge is to investigate the possibility to have the ferromagnetic or/and ferrimagnetic behavior connected to Sn0.98Mn0.02(O1-xCx)2 system at low concentration (x = 0.02, 0.03, 0.04 and 0.05) at room temperature (RT). We utilized the Korringa-Kohn-Rostoker method combined with the Coherent Potential Approximation (KKR-CPA). The C-doped SnO2 induced the half-metallic characteristic located on the Fermi level and the presence of the double-exchange coupling type belongs to the ferromagnetic (FM). The Sn0.98Mn0.02O2 shows the antiferromagnetic (AFM) stability belongs to super-exchange coupling type. For Sn0.98Mn0.02(O1-xCx)2 system, we predicted two statements, the presence of the FM stability where (x = 0.03) and the ferrimagnetic stability where (x = 0.02, 0.04, 0.05). The Curie temperature (TC) can be estimated within the mean field approximation (MFA), our calculations predicted 358.45 K for Sn(O0.95C0.05)2 and 402.26 K for Sn0.98Mn0.02(O0.95C0.05)2. The ferrimagnetic materials are useful for many applications.

Magnetism and phase diagrams of the doubles perovskite Sr[formula omitted][formula omitted]: Monte Carlo simulations

The double perovskite Sr2CrIrO6 has very important characteristics for spintronic applications. It is a ferrimagnetic material distinguished by its high Curie temperature. This manuscript presents a model representing the double perovskite Sr2CrIrO6 in order to simulate and to predict its magnetic properties. This compound contains only two magnetic atoms, namely: Cr (S = 3/2) and Ir (σ=2). Our simulations are done using the Monte Carlo method under the Metropolis algorithm. We present the behavior of the magnetization and the susceptibilities as a function of the temperature. Also, we discuss the effect of the physical parameters such as the coupling exchange interactions, the crystal field and the external magnetic field. To complete this study, we have presented the ground state by exposing the different phase diagrams in different planes of the physical parameters. Moreover, we establish the magnetic hysteresis loops of this compound.

Microscopic and mesoscopic understanding of magnetization compensation phenomenon in ferrimagnetic Li0.5FeCr1.5O4 spinel

Structural and magnetic properties of the spinel compound, Li0.5FeCr1.5O4, have been investigated using dc magnetization, neutron depolarization, and neutron diffraction techniques. DC magnetization measurement at 200 Oe has revealed a ferrimagnetic ordering at 417 K and a negative magnetization state between the two compensation temperatures (TComp) of 244 and 256 K. TComp varies with an applied magnetic field and two TComp merge at 256 K for magnetic fields ≥ 500 Oe. The existence of zero domain magnetization around TComp is evident from full recovery of the transmitted neutron beam polarization in a neutron depolarization study. The Rietveld refinement of the neutron diffraction pattern at 430 K reveals that the compound possesses a face centred cubic structure with Fe0.81Li0.19 and Cr1.5Li0.31Fe0.19 as cation distributions at the tetrahedral and octahedral sites, respectively. A temperature dependent neutron diffraction study reveals that the net magnetic moment changes sign near 265 K, across the spin compensation temperature. Both neutron diffraction and mean field calculation show that an asymmetric variation of the sublattice moments as a function of temperature yields a dominance of the ordered tetrahedral site moment over the octahedral site moment below TComp, and vice versa above TComp, and gives a microscopic understanding of the observed magnetization reversal phenomenon. The achieved understanding of magnetization compensation and the high coercivity near TComp have implications for possible use of such ferrimagnetic materials with finite spin polarization as effective spin polarizers/analyzers in spintronic devices.

Ferrimagnetism in a system of two antiferromagnetically coupled Heisenberg models

We phenomenologically investigate the phase diagram of some ferrimagnetic materials on the basis of two bilinearly coupled Heisenberg models sitting on two interpenetrating simple magnetic cubic lattices. Computations were performed with the help of the Landau free energy obtained through applying the Hubbard-Stratonovich transformation to the initial microscopic Heisenberg Hamiltonian. The transitions to the magnetically ordered phases within the model are found to be of second order with the occurrence of a compensation point at lower temperatures for some values of the system’s parameters. It is found that the main stable phase is a two-sublattice collinear ferrimagnet in addition to a metastable non-collinear phase. The numerical results give a detailed description of temperature dependence of magnetization on the strength of intersublattice interaction and the difference between the effective exchanges of two ferromagnetically ordered sublattices. Our results are in qualitative agreement with the experimental results on Y3Fe5O12 in the strong coupling limit and the compounds ErFe2 and GdCo12B6 for weak couplings.

Magnetoimpedance effect in ferrimagnetic insulator yttrium iron garnet films capped by copper

Abstract We investigate the magnetization dynamics through magnetoimpedance effect in films of ferrimagnetic insulator yttrium iron garnet capped by copper. Thereby, we explore the magnetoimpedance in systems with magnetic insulators by varying the thickness of the magnetic material, and probe current frequency. We observe that the difference of electrical nature of the layers composing the films gives rise to the magnetoinductive effect in the whole frequency range, as well as favors the appearance of the ferromagnetic resonance effect even at low frequencies. We discuss the experimental results in terms of the structural features of the magnetic material, its magnetic properties, and the different mechanisms governing the magnetization dynamics. The results place the films of ferrimagnetic insulator yttrium iron garnet capped by copper exhibiting magnetoimpedance effect as very attractive candidates for application as probe element in magnetic sensors operating at low frequencies and with energy-efficient technologies. Further, we disclose an auspicious technique to look at the magnetization dynamics in magnetic materials and we provide a new perspective to solve questions related to the integration of insulator ferrimagnetic materials with the coplanar waveguide in broadband frequency applications.

3d-Metal Induced Magnetic Ordering on U(IV) Atoms as a Route toward U(IV) Magnetic Materials.

Uranium(IV) 5f2 magnetism is dominated by a transition from a triplet to a singlet ground state at low temperatures. For the first time, we achieved magnetic ordering of U(IV) atoms in a complex fluoride through the incorporation of 3 d transition metal cations. This new route allowed us to obtain an unprecedented series of U(IV) ferrimagnetic materials of the new composition Cs2MU3F16 (M = Mn2+, Co2+, and Ni2+), which were comprehensively characterized with respect to their structural and magnetic properties. Magnetic susceptibility measurements revealed ferromagnetic-like phase transitions at temperatures of ∼14.0, 3.5, and 4.8 K for M = Mn2+, Co2+, and Ni2+, respectively. The transition is not observed when the magnetic M cations are replaced by a diamagnetic cation, Zn2+. Neutron diffraction measurements revealed the magnetic moments of 0.91(6)-1.97(3) μB on the U atoms, which are only partially compensated by antiparallel moments of 1.53(14)-3.26(5) μB on the 3 d cations. This arrangement promotes suppression of the transition to a diamagnetic ground state characteristic of U(IV), and in doing so, induces magnetic ordering on uranium via 3 d-5 f exchange coupling.

Study of Surface Character of Micrometer-Scale Dipole-Exchange Spin Waves in an Yttrium Iron Garnet Film

We demonstrate that micrometer-scale spin waves can be excited in a thin film of the ferrimagnetic material yttrium iron garnet (YIG) using patterned, multi-element antennas. The magnitude of the dynamic magnetic field generated by such antennas decays exponentially along the thickness direction, and this leads to an enhanced coupling to modes having a surface-like character as opposed to a more sinusoidal bulk-like character. We have used this property to identify spin waves having a mixed bulk/surface character.

Physical-chemical properties of M@Fe3O4 core@shell nanowires (M = Cu, Co, CoO).

Interest in low dimensional magnetic systems has been growing due to the novel and dramatically differentiated effects of their physical properties, which give them special behaviors and uses in biomedical, environmental and technological fields. In this study we report extensive first-principles calculations on the geometric optimization as well as electronic, magnetic, mechanical and thermal properties of several quasi one-dimensional core/shell nanowires: Cu/Fe3O4, Co/Fe3O4, and CoO/Fe3O4. The main focus lies on the quantum confinement effects as well as on the effect of the interaction between the ferrimagnetic semiconductor shell material (magnetite nanotube) and core compounds with differentiated magnetic behavior such as (i) a ferromagnetic material (Co), (ii) an antiferromagnetic transition metal oxide (CoO) and (iii) a non-magnetic simple metal (Cu). The mechanical properties of the related nanosystems are studied through the effects of axial deformations, and their thermal behavior is evaluated by considering the electronic contribution of each sample to the heat capacity, and some potential technological applications are suggested.

Spectra of Collective Excitations and Low-Frequency Asymptotics of Green’s Functions in Uniaxial and Biaxial Ferrimagnetics

The paper studies the dynamic description of uniaxial and biaxial ferrimagnetics with spin s=1/2 in alternative external field. The nonlinear dynamic equations with sources are obtained, on basis on which low-frequency asymptotics of two-time Green functions in the uniaxial and biaxial cases of the ferrimagnet are obtained. Energy models are constructed that are specific functions of Casimir invariants of the algebra of Poisson brackets for magnetic degrees of freedom. On their basis, the question of the stable magnetic states has been solved for the considered systems. These equations were linearized, an explicit form of the collective excitations spectra was found, and their character was analyzed. The article studies the uniaxial case of a ferrimagnet, as well as biaxial cases of an antiferromagnet, easy-axis and easy-plane ferrimagnets. It is shown that for a uniaxial antiferromagnet the spectrum of magnetic excitations has a Goldstone character. For biaxial ferrimagnetic materials, it was found that the spectrum has either a quadratic character or a more complex dependence on the wave vector. It is shown that in the uniaxial case of an antiferromagnet the Green function of the type Gsα,sβ(k,0), Gsα,nβ(k,0) and Gsα,sβ(0,ω) have regular asymptotic behavior, and the Green function of type Gnα,nβ(k,0)≈1/k2 and Gsα,nβ(0,ω)≈1/ω, Gnα,nβ(0,ω)≈1/ω2 have a pole feature in the wave vector and frequency. Biaxial ferrimagnetic states have another type of the features of low-frequency asymptotics of the Green's functions. In the case of a ferrimagnet, the “easy-axis” of the asymptotic behavior of the Green functions Gsα,sβ(0,ω), Gsα,nβ(0,ω), Gnα,nβ(0,ω), Gsα,sβ(k,0), Gsα,nβ(k,0), Gnα,nβ(k,0) have a pole character. For the case of the “easy-plane” type ferrimagnet, the asymptotics of the Green functions Gsα,nβ(0,ω), Gnα,nβ(0,ω), Gsα,nβ(k,0), Gnα,nβ(k,0), have a pole character, and the Green function Gsα,sβ(k,ω) contains both the pole component and the regular part. A comparative analysis of the low-frequency asymptotics of Green functions shows that the nature of magnetic anisotropy significantly effects the structure of low-frequency asymptotics for uniaxial and biaxial cases of ferrimagnet. Separately, we note the non-Bogolyubov character of the Green function asymptotics for ferrimagnet with biaxial anisotropy Gnα,nβ(k,0)≈1/k4.

Coercivity enhancement and magnetic property evaluation of Bi doped Mn2Sb

Abstract Mn2Sb is a well-known ferrimagnetic material, which has been investigated thoroughly to understand the effect of doping on its magnetic properties. Present work reports the synthesis of Bi doped Mn2Sb employing arc-melting and melt spinning followed by characterization with a view to establish a correlation in the structure and magnetic properties. Bi doping in Mn2Sb lattice produces a significant change in the latter’s magnetic properties, giving rise to a saturation magnetization of 27.2 emu/g (27.2 Am2/Kg) and a high coercivity value of 3.4 kOe (279.2 kA/m), in comparison to Mn2Sb, which has a coercivity of 0.1 kOe (7.96 kA/m). Theoretical studies were carried out to understand the changes in magnetic properties. Ab-initio electronic and atomic structure calculations show that Bi atom occupies equally the MnI and MnII sites and this leads to ferromagnetic ordering, which results in enhancement of the saturation magnetisation. The coercivity mechanism has also been studied in detail; the large coercivity is attributed to the nucleation mechanism achieved via the inclusion of diamagnetic Bi particles in Mn2Sb.

Physical Conditions for Realization of Large Magnetocaloric Effect in Magnets

Physical quantities affecting the magnitude of magnetocaloric effect in ferro- and ferrimagnetic materials with first and second order magnetic phase transitions are considered. Governing equations for the main characteristics of the magnetocaloric effect are given and analyzed. Their outcomes are compared with the experimental results.

Spin–Orbit Torque Switching in a Nearly Compensated Heusler Ferrimagnet

Ferrimagnetic materials combine the advantages of the low magnetic moment of an antiferromagnet and the ease of realizing magnetic reading of a ferromagnet. Recently, it was demonstrated that compensated ferrimagnetic half metals can be realized in Heusler alloys, where high spin polarization, zero magnetic moment, and low magnetic damping can be achieved at the same time. In this work, by studying the spin-orbit torque induced switching in the Heusler alloy Mn2 Ru1- x Ga, it is found that efficient current-induced magnetic switching can be realized in a nearly compensated sample with strong perpendicular anisotropy and large film thickness. This work demonstrates the possibility of employing compensated Heusler alloys for fast, energy-efficient spintronic devices.

Unidirectional Loop Metamaterials (ULM) as Magnetless Artificial Ferrimagnetic Materials: Principles and Applications

This paper presents an overview of Unidirectional Loop Metamaterial (ULM) structures and applications. Mimicking electron spin precession in ferrites using loops with unidirectional loads (typically transistors), the ULM exhibits all the fundamental properties of ferrite materials, and represents the only existing magnetless ferrimagnetic medium. We present here an extended explanation of ULM physics and unified description of its component and system applications.

Si-related ferrimagnetic material consisting of Eu and Fe layers

In order to explore Si-related spintronic materials, we use a full-potential density-functional-theory method to study electronic structure and magnetic properties of EuFe2Si2 with the layered ThCr2Si2 structure. Our comparative optimization investigation among 25 magnetic configurations reveals that its ground state phase is a ferrimagnet, in which the spins in both of Eu and Fe layers are aligned ferromagnetically, but the Eu spins are aligned antiferromagnetically with the Fe spins. This is very different from the striped antiferromagnetic ground state for the Fe spins in FeAs-based materials. The filled Eu 4f bands in the majority-spin channel, very flat, are just below the Fermi level and the Fe 3d bands cover an energy range of 4 eV astride the Fermi level. The Eu atom is ionic and contributes a moment of nearly 7μB, and Fe is bonded strongly with Si, which results in a low-moment state for Fe. Our results are of interest to explore the physical properties of the Fe-based materials, and can stimulate further effort to seek useful Si-related spintronic materials.

Order Parameter Profiles near Surfaces of Super-weak Ferrimagnetic Materials Exhibiting a Paramagnetic-Ferrimagnetic Transition

The aim of this paper is to determine the full order parameter profiles close to the surface for a system made of two strongly coupled paramagnetic sublattices of respective moments and . The material exhibits a para-ferrimagnetic transition at some critical temperature Tc greater than the room temperature. The free energy describing the physics of the system is of Landau type, and involves, beside quadratic and quartic terms in both and , a lowest-order coupling, -Co where CoL, and the free energy is then a sum of bulk and surface contributions expanded in terms of the local order parameters. The magnetization at the surface are s and s. As in a recent paper (whom the present work is an extension), we first reduce the model to an effective 4 -theory written in terms of the overall magnetization =+ and the associated fraction of magnetization a=/(+). For the ordinary transition where the extrapolation length is positive s>0, we determine the order parameter profile near surfaces. We show, in particular, that the magnetization behavior is governed, in addition of s and the bulk correlation length b-, by a new length La. We have interpreted this latter as the width of the ordered ferrimagnetic layer close to the surface. Finally, we examine the extraordinary (ss=) and surface (at Tcs>Tc) transitions.

Use of Vanadium Oxide as a Liquid Phase Sintering Aid for Barium Hexaferrite

The use of V₂OSUB5/SUB as a liquid phase sintering aid for BaFeSUB12/SUBOSUB19/SUB is studied. Three weight % of V₂OSUB5/SUB is added to a BaFeSUB12/SUBOSUB19/SUB powder, samples are sintered at temperatures between 900-1250 °C and the effects of sintering aid addition on densification, microstructure, phase purity and magnetic properties are examined. Compared to BaFeSUB12/SUBOSUB19/SUB without sintering aid addition, addition of 3 wt% V₂OSUB5/SUB leads to a moderate improvement in densification behavior. Samples with 3 wt% V₂OSUB5/SUB addition contain considerable amounts of Fe₂O₃ and Ba₃(VO₄)₂ second phases. The BaFeSUB12/SUBOSUB19/SUB sample without sintering aid addition has a Magnetization-Field hysteresis loop typical of a hard ferrimagnetic material, whereas the 97 wt% BaFe12O19 - 3 wt% V₂OSUB5/SUB sample has a hysteresis loop with reduced saturation magnetization and coercivity.

The compensation temperature behavior in a diluted extended ferrimagnetic material structure

In this work, we study the magnetic properties in a diluted ferrimagnetic materials structure, composed with three areas, by Monte Carlo simulations. The system consists of two non-equivalent types of atoms A and B, two arrangements ABA and BAB are considered. The dilution effect concerns only the B atoms. The ground state phase diagrams are reported. The effect of exchange coupling interactions on the compensation temperature is investigated. The obtained results show that the system presents a compensation temperature and different behaviors when varying the coupling parameters and the dilution probability.

Current-Induced Domain Wall Motion in a Compensated Ferrimagnet.

Owing to the difficulty in detecting and manipulating the magnetic states of antiferromagnetic materials, studying their switching dynamics using electrical methods remains a challenging task. By employing heavy-metal-rare-earth-transition-metal alloy bilayers, we experimentally study current-induced domain wall dynamics in an antiferromagnetically coupled system. We show that the current-induced domain wall mobility reaches a maximum at the angular momentum compensation point. With experiment and modeling, we further reveal the internal structures of domain walls and the underlying mechanisms for their fast motion. We show that the chirality of the ferrimagnetic domain walls remains the same across the compensation points, suggesting that spin orientations of specific sublattices rather than net magnetization determine Dzyaloshinskii-Moriya interaction in heavy-metal-ferrimagnet bilayers. The high current-induced domain wall mobility and the robust domain wall chirality in compensated ferrimagnetic material opens new opportunities for high-speed spintronic devices.