Ferromagnetic Hysteresis Loops Research Articles

Enhanced magnetic response in single-phase Bi0.80La0.15A0.05FeO3−δ (A=Ca, Sr, Ba) ceramics

Abstract Single phase Bi0.80La0.15A0.05FeO3−δ (A=Ca, Sr, Ba) dense ceramics were synthesized via solid state reaction method. Structural studies through X-ray diffraction shows that all prepared ceramics crystallized in a rhombohedrally (R 3 ¯ C)distorted BiFeO3 structure with compressive lattice distortion induced by the rare earth (La3+) ion and divalent co-doping at the Bi-site for the Raman study. Scanning electron micrograph of the compounds showed the uniform distribution of grains on the sample surface with high density. A large ferromagnetic hysteresis loop is observed for La/Ba co-doped BiFeO3 as compared with BiFeO3 prepared under similar conditions, with saturation magnetization of 6.85 emu/g and remnant magnetization of 2.72 emu/ g at 300 K. Clear ferromagnetic ground state was observed in Bi0.80La0.15Ba0.05FeO3 and weak ferromagnetism in BLCFO and BLSFO samples. Dielectric constant and dielectric loss were found to decrease with increase in frequency for all the compounds. These improved properties of La/Ba co-doped BFO demonstrate the possibility of enhancing the magnetic applicability and makes very promising for industrial applications such as new devices in information storage.

(Ba1−xKx)(Cu2−xMnx)Se2: A copper-based bulk form diluted magnetic semiconductor with orthorhombic BaCu2S2-type structure

A new copper-based bulk form diluted magnetic semiconductor (DMS) (Ba1−xKx)(Cu2−xMnx)Se2 (x=0.075, 0.10, 0.125, and 0.15) with TC ∼18K has been synthesized. K substitution for Ba introduces hole-type carriers, while Mn substitution for Cu provides local spins. Different from previous reported DMSs, this material crystallizes into orthorhombic BaCu2S2-type crystal structure. No ferromagnetism is observed when only doping Mn, and clear ferromagnetic transition and hysteresis loop have been observed as K and Mn are codoped into the parent compound BaCu2Se2.

Effects of donor W6+-ion doping on the microstructural and multiferroic properties of Aurivillius Bi7Fe3Ti3O21 thin film

Aurivillius phase Bi7Fe3(Ti3−xWx)O21+δ (x=0 and 0.06) thin films were deposited on Pt(111)/Ti/SiO2/Si(100) substrates by using a chemical solution deposition method. The W6+-ion doped Bi7Fe3Ti3O21 thin film exhibited tremendous improvements in the electrical and multiferroic properties, namely a low leakage current density, good stability against electrical breakdown, large ferroelectric polarization and large magnetization as compared to the un-doped thin film. The Bi7Fe3(Ti2.94W0.06)O21+δ thin film was stable against electrical break down at applied electric fields up to 1275kV/cm, at which the measured remnant polarization (2Pr) and the coercive field (2Ec) values were 33.5μC/cm2 and 825kV/cm, respectively whereas, the measured 2Pr value of the un-doped Bi7Fe3Ti3O21 thin film was 3.5μC/cm2 at an applied electric field of 318kV/cm. Furthermore, the Bi7Fe3(Ti2.94W0.06)O21+δ thin film showed a well-saturated ferromagnetic hysteresis loop with large magnetization at room temperature.

Nd and Sc co-doped BiFeO3 nanopowders displaying enhanced ferromagnetism at room temperature

We have developed a novel synthetic route for the preparation of single phase NdxBi1−xFe0.95Sc0.05O3 (NBFSO) nanopowder materials by a surfactant-assisted combustion-derived method. Rietveld fitting of the Powder X-ray diffraction data showed the nanopowder structure evolves from a distorted rhombohedral BiFeO3 crystalline structure (R3c, x=0) to a orthorhombic structure (Pbnm, x=0.10). Differential thermal analysis and thermogravimetric analysis (DTA/TGA) showed a crystallization temperature of 200°C. Transmission electron microscopy (TEM) images revealed the presence of clusters formed by fine nanoparticles less than 60nm in diameter. From Raman spectroscopy, the change from rhombohedral structure to cubic structure was observed by a drastic intensity reduction of the A1−2 and A1−3 Raman modes, with the A1−1 and A1−2 modes gradually merging together, indicating the merge of the orthorhombic phase. Despite the antiferromagnetic nature of bulk BiFeO3, the NBFSO nanopowders obtained displayed a ferromagnetic hysteresis loop, with coercivities of 0.08T and remanent magnetizations of 0.65–4.05Am2/kg when measured at room temperature. The increasing and uncompensated spins at the surface of nanoparticles and the canted internal spin by the tilt of FeO6 octahedral units and the structure transition appear to be the main reason for observed this ferromagnetic behavior.

Preparation of LSMO/PLZT Composite Film by Sol-Gel Technique and its Ferroelectric and Ferromagnetic Properties

La0.67Sr0.33MnO3 (LSMO)/Pb0.92La0.08Zr0.65Ti0.35O3 (PLZT) composite film was fabricated on a (001) LaAlO3 (LAO) single crystal substrate by a sol-gel technique. The results from X-ray diffraction (XRD) indicated that LSMO and PLZT could grow successively on LAO substrate with (001) preferred orientation. The ferroelectric and ferromagnetic properties of LAO/LSMO/PLZT composite film were also investigated. The results showed that the remnant polarization Pr, and coercive field Ec of the composite film at room temperature were 36.38 μC/cm2 and 512.43 kV/cm respectively. Moreover, the composite film exhibited significant ferromagnetic hysteresis loops and soft magnetic behavior at temperatures lower than 250 K.

Magnetic and superconductivity studies on (In1−xFex)2O3 thin films

Magnetic, magnetoresistivity and superconductivity studies were carried out on (In1−xFex)2O3 (x=0.00, 0.03, 0.05 and 0.07) thin films (2D structures) grown on glass substrate by electron beam evaporation technique at 350°C. The films have an average size of 120nm particles. All the samples shown soft ferromagnetic hysteresis loops at room temperature and saturation magnetization increased with iron dopant concentration. Observed magnetization could be best interpreted by F-center mediated magnetic exchange interaction in the samples. Temperature dependent resistivity of the sample (x=0.00 and 0.07) showed metallic behavior down to very low temperatures and superconductivity at 2K for undoped In2O3 whereas the In1.86Fe0.14O3 sample shows superconductivity below 2K in the absence of magnetic fields. The reduction in transition temperature was attributed to increase electrical disorder with iron doping. Both samples showed positive magnetoresistivity (MR) in superconducting state due to increase of resistivity resulting from breaking of superconducting Cooper pairs upon application of magnetic field. In addition, both the samples show feeble negative MR in normal electrical state. The observed MR in normal state is not due to spin polarized tunneling instead it is due to suppression of scattering of charge carrier by single occupied localized states.

Theoretical study of mutual control mechanism between magnetization and polarization in multiferroic materials**Project supported by the National Basic Research Program of China (Grant No. 2012CB927402) and the National Natural Science Foundation of China (Grant Nos. 61275028 and 11074145).

The mutual control mechanism between magnetization and polarization in multiferroic materials is studied. The system contains a ferromagnetic sublattice and a ferroelectric sublattice. To describe the magneto–electric coupling, we propose a linear coupling Hamiltonian between ferromagnetism and ferroelectricity without microscopic derivation. This coupling enables one to retrieve the hysteresis loops measured experimentally. The thermodynamic properties of the system are calculated, such as the temperature dependences of the magnetization, polarization, internal energy and free energy. The ferromagnetic and ferroelectric hysteresis loops driven by either a magnetic or an electric field are calculated, and the magnetic spin and pseudo-spin are always flipped synchronously under the external magnetic and electric field. Our theoretical results are in agreement with the experiments.

Multiferroic properties of a BiCrO3/BiFeO3 double-layered thin film prepared by chemical solution deposition

This study involved an investigation of the structural, electrical, and multiferroic properties of a BiCrO3/BiFeO3 (BCO/BFO) double-layered thin film that was prepared on a Pt(111)/Ti/SiO2/Si(100) substrate by using a chemical solution deposition method. X-ray diffraction and Raman spectroscopy studies revealed the formation of tetragonal and rhombohedral structures for the BCO/BFO double-layered thin film without any detectable secondary phases. A saturated ferroelectric hysteresis loop with a remnant polarization (2Pr) of 37μC/cm2 and a coercive field (2Ec) of 1004kV/cm at an applied electric field of 1154kV/cm and a ferromagnetic hysteresis loop with a 2Mr value of 0.044emu/cm2 and a 2Hc value of 276Oe at a magnetic field of 10kOe were observed for the BCO/BFO double-layered thin film at room temperature. The leakage current density of the BCO/BFO double-layered thin film was 2.88×10−4A/cm2 at an external electric field of 100kV/cm. The enhanced multiferroic properties observed for the BiCrO3/BiFeO3 thin film correlated with its net effects, such as a decrease in the oxygen vacancy density, a stabilization of the perovskite structure, and small changes in the lattice parameter caused by compressive strain resulting from the coupling of the BiFeO3 and BiCrO3 layers.

Investigation of structural, electrical and multiferroic properties of Co-doped Aurivillius Bi6Fe2Ti3O18 thin films

In this study, the structural, electrical and multiferroic properties of Bi6Fe2Ti3O18 and Bi6Fe1.5Co0.5Ti3O18−δ thin films were investigated. A chemical solution deposition method was used to prepare the thin films on Pt(111)/Ti/SiO2/Si(100) substrates. Both of the thin films crystallized with single phase Aurivillius orthorhombic structures were confirmed by means of X-ray diffraction and Raman spectroscopy studies. X-ray diffraction study further revealed Co2+-ion doping to have a significant influence on the orientation of the Bi6Fe2Ti3O18 thin film. Electrical studies revealed that the leakage current density of the Bi6Fe1.5Co0.5Ti3O18−δ thin film was about two orders of magnitude lower than that of the Bi6Fe2Ti3O18 thin film. An enhanced remnant polarization (2Pr) of 7.4μC/cm2 and a remnant magnetization (2Mr) of 0.97emu/cm3 was obtained for the Bi6Fe1.5Co0.5Ti3O18−δ thin film by measuring the ferroelectric and ferromagnetic hysteresis loops at room temperature.

Characterization and magnetic properties of Nd Bi1−Fe0.95Co0.05O3 nanopowders synthesized by combustion-derived method at low temperature

Nd x Bi 1− x Fe 0.95 Co 0.05 O 3 ( x =0, 0.05, 0.10, 0.15) nanopowders were prepared by a combustion-derived method. The Rietvelt fitting of the X-Ray diffraction data from the Nd x Bi 1− x Fe 0.95 Co 0.05 O 3 (NBFCO) powders showed nanopowders with rhombohedral BiFeO 3 crystalline structure (R3c) for x ≤10 and a partial structural transition to orthorhombic phase (Pnma) for x =0.15. The differential thermal analysis and thermogravimetric analysis (DTA/TGA) showed a crystallization temperature of 180 °C. Transmission electronmicroscopy (TEM) images revealed that the NBFCO nanopowders were composed of fine particles under 60 nm. From Raman spectroscopy , a band of disordered anion lattice was observed at 653 cm −1 . In spite of the antiferromagnetic nature of bulk BiFeO 3 , the NBFCO nanopowders obtained displayed a ferromagnetic hysteresis loop, with coercivity about 0.1 T and remanent magnetization of 1.02–4.33 A m 2 /kg were obtained at room temperature. This ferromagnetic behavior is due to increasing and uncompensated spins at the surface and the canted internal spin by the tilt of FeO 6 octahedral units. We have developed a novel synthetic route for the preparation of ferromagnetic BFO-derived nanopowder materials by a surfactant-assisted combustion-derived method. • The structure of materials obtained is studied. • A new synthesis method was proposed to obtain ferrimagnetic–ferromagnetic BiFeO 3 nanoparticles. • Synthesis temperature does not exceed 200 °C. • The obtained nanoparticles have sizes less than 52 nm.

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NdxBi1−xFe0.95Co0.05O3 (x=0, 0.05, 0.10, 0.15) nanopowders were prepared by a combustion-derived method. The Rietvelt fitting of the X-Ray diffraction data from the NdxBi1−xFe0.95Co0.05O3 (NBFCO) powders showed nanopowders with rhombohedral BiFeO3 crystalline structure (R3c) for x≤10 and a partial structural transition to orthorhombic phase (Pnma) for x=0.15. The differential thermal analysis and thermogravimetric analysis (DTA/TGA) showed a crystallization temperature of 180 °C. Transmission electronmicroscopy (TEM) images revealed that the NBFCO nanopowders were composed of fine particles under 60 nm. From Raman spectroscopy, a band of disordered anion lattice was observed at 653 cm−1. In spite of the antiferromagnetic nature of bulk BiFeO3, the NBFCO nanopowders obtained displayed a ferromagnetic hysteresis loop, with coercivity about 0.1 T and remanent magnetization of 1.02–4.33 A m2/kg were obtained at room temperature. This ferromagnetic behavior is due to increasing and uncompensated spins at the surface and the canted internal spin by the tilt of FeO6 octahedral units. We have developed a novel synthetic route for the preparation of ferromagnetic BFO-derived nanopowder materials by a surfactant-assisted combustion-derived method.

FeGa/MgO/Fe/GaAs(001) magnetic tunnel junction: Growth and magnetic properties

Research on spintronics and on multiferroics leads now to the possibility of combining the properties of these materials in order to develop new functional devices. Here we report the integration of a layer of magnetostrictive material into a magnetic tunnel junction. A FeGa/MgO/Fe heterostructure has been grown on a GaAs(001) substrate by molecular beam epitaxy (MBE) and studied by X-ray magnetic circular dichroism (XMCD). The comparison between magneto optical Kerr effect (MOKE) measurements and hysteresis performed in total electron yield allowed distinguishing the ferromagnetic hysteresis loop of the FeGa top layer from that of the Fe buried layer, evidencing a different switching field of the two layers. This observation indicates an absence of magnetic coupling between the two ferromagnetic layers despite the thickness of the MgO barrier of only 2.5nm. The in-plane magnetic anisotropy has also been investigated. Overall results show the good quality of the heterostructure and the general feasibility of such a device using magnetostrictive materials in magnetic tunnel junction.

Structural and Magnetic properties of Cr-diffused CdTe nanocrystalline thin films deposited by electron beam evaporation

Cr-diffused cadmium telluride (CdTe) thin films with different Cr content were prepared using electron beam evaporation method at a substrate temperature of 373 K followed by annealing at 573 K. The structures, composition, chemical and magnetic properties of the prepared films were studied using appropriate techniques. The X-ray diffraction spectra showed a predominant (1 1 1) reflection corresponding to the zinc blende structure of CdTe. Increase of lattice parameter with increase in Cr content has been observed. The cross-sectional HRSEM images displayed a columnar grain growth in the films. EDAX data exposed the presence of Cr, Cd and Te with near stoichiometry. The Raman spectra revealed emission peaks corresponding to A1, TO and LO modes of CdTe showing gradual shift in peak position and decreased intensity confirming the incorporation of Cr into CdTe host lattice. M–H plots displayed a clear well-defined room temperature ferromagnetic hysteresis loop with increase in Cr content.

Local polar structure and multiferroic properties of (1−x)Bi0.9Dy0.1FeO3−xPbTiO3 solid solution

The multiferroic (1–x)[0.9BiFeO3–0.1DyFeO3]–xPbTiO3 (BDF–xPT) solid solution with compositions around the morphotropic phase boundary (x = 0.25, 0.28, 0.31, 0.34, and 0.37) has been synthesized in the form of ceramics. The phase symmetry, microstructure, ferroelectricity, piezoresponse, and ferromagnetic properties have been characterized by various techniques. It is found that, with increasing content of lead titanate from x = 0.25 to x = 0.37, the grain size increases and the ferroelectric property is improved. The ferroelectric performance is further enhanced by the introduction of an excess amount (2%) of TiO2 or by sintering in oxygen atmosphere, which reduces the leakage. The local polar structure is imaged by piezoresponse force microscopy. Both the out-of-plane and in-plane images reveal distinct ferroelectric domain structures, with the amplitude and the average domain size decreasing with the increase of lead titanate amount. Compared with the (1–x)BiFeO3–xPbTiO3 binary solid solution of about the same concentration of PT, the magnetic properties are enhanced in BDF–xPT due to the presence of dysprosium, as demonstrated by the ferromagnetic hysteresis loops displayed at room temperature and at 10 K, but the remnant magnetization decreases with increasing PT content. The simultaneous presence of ferroelectricity and ferromagnetism entitles the BDF–xPT solid solution a room-temperature multiferroic material.

Structural, optical and magnetic properties of Cr doped SnO2 nanoparticles stabilized with polyethylene glycol

Pure and Cr (1, 3, 5 and 7 at%) doped SnO2 nanoparticles were synthesized in aqueous solution by a simple chemical co-precipitation method using polyethylene glycol (PEG) as a stabilizing agent. The effect of Cr doping on the structural, optical and magnetic properties of SnO2 nanoparticles was investigated. EDAX spectra confirmed the presence of Sn, O and Cr in near stoichiometry. XRD patterns revealed that particles of all samples were crystallized in single phase rutile type tetragonal crystal structure (P42/mnm) of SnO2. The peak positions with Cr concentration shifted to higher 2θ values. Lattice parameters were also decreased with increasing Cr concentration. TEM studies indicated that the particle size is in the range of 8–10nm. The optical absorption studies indicated that the absorption edge shifted towards lower wavelengths with inclusion of Cr content. FTIR spectrum displays various bands that are due to fundamental overtones of PEG and O–Sn–O entities. Further it revealed that the undoped and as well as Cr doped SnO2 nanoparticles were capped by PEG. Magnetization measurements at room temperature revealed that all the doped samples were ferromagnetic in nature. Well defined strong room temperature ferromagnetic hysteresis loop was observed for 1% Cr doped SnO2 nanoparticles.

Optimization of excess Bi doping to enhance ferroic orders of spin casted BiFeO3 thin film

Multiferroic Bismuth Ferrite (BiFeO3) thin films with varying excess bismuth (Bi) concentration were grown by chemical solution deposition technique. Room temperature multiferroic properties (ferromagnetism, ferroelectricity, and piezoelectricity) of the deposited BiFeO3 thin films have been studied. High resolution X-ray diffraction and Raman spectroscopy studies reveal that the dominant phases formed in the prepared samples change continuously from a mixture of BiFeO3 and Fe2O3 to pure BiFeO3 phase and, subsequently, to a mixture of BiFeO3 and Bi2O3 with increase in the concentration of excess Bi from 0% to 15%. BiFeO3 thin films having low content (0% and 2%) of excess Bi showed the traces of ferromagnetic phase (γ-Fe2O3). Deterioration in ferroic properties of BiFeO3 thin films is also observed when prepared with higher content (15%) of excess Bi. Single-phased BiFeO3 thin film prepared with 5% excess Bi concentration exhibited the soft ferromagnetic hysteresis loops and ferroelectric characteristics with remnant polarization 4.2 μC/cm2 and saturation magnetization 11.66 emu/g. The switching of fine spontaneous domains with applied dc bias has been observed using piezoresponse force microscopy in BiFeO3 thin films having 5% excess Bi. The results are important to identify optimum excess Bi concentration needed for the formation of single phase BiFeO3 thin films exhibiting the improved multiferroic properties.

New optical transition, structural, and ferromagnetic properties of InCrP:Zn implanted with Cr

InCrP:Zn was prepared using the implantation with Cr concentrations of 0.3% and 0.7%, respectively. It was confirmed that the photoluminescence peaks near 0.85(D, Cr)eV and 0.96(e,Cr)eV were Cr-correlated PL bands by the implantation of Cr. Especially, each 0.85(D, Cr)eV and 0.96(e,Cr)eV peaks were separately observed based on InP. In triple-axis x-ray diffraction patterns, the samples revealed a shoulder peak indicative of intrinsic InCrP. Ferromagnetic hysteresis loops measured at 10K and 300K were observed and the temperature-dependent magnetization showed ferromagnetic behavior ≥300K, which reveals obvious and enhanced ferromagnetic spin coupling mediated by hole.

Structural and Magnetic Properties of Co diffused CdTe Nanocrystalline Thin Films Deposited by Electron Beam Evaporation

Co diffused cadmium telluride (CdTe) nanocrystalline thin films with different Co content were prepared by depositing CdTe/Co stacked layers on glass substrates at 373 K using electron beam evaporation technique. The effect of Co content on structural, morphological, chemical, Raman, and magnetic studies were carried out. X-ray diffraction (XRD) patterns confirmed that all Co diffused CdTe films are in zinc blende structure. The lattice parameter increased with increase of Co content. The high-resolution scanning electron microscopy (HRSEM) images illustrated the grain size of the films. EDAX data confirmed the presence of Co, Cd, and Te with nearly stoichiometic. Raman spectra revealed peaks corresponding to A1, TO, and LO modes of CdTe and gradual shift in peak position. The increase in intensity confirmed the incorporation of Co into CdTe host lattice. Magnetic measurements showed a clear well-defined room temperature ferromagnetic hysteresis loop.

Magnetism in a Spintronic Compound Zr<sub>0.8</sub>Cr<sub>0.2</sub>O<sub>2</sub> of Small Crystallites

A transition metal ion Cr4+(3d2 spins) doped ZrO2 of small crystallites presents tailored magnetic, electrical and optical properties useful for magnetodielectric and spintronic applications. A liquid polymer precursor gel (Cr4+ and Zr4+ complex with glycerol) when heated in an autoclave at a small pressure 0.6-0.7 atm at 420–470 K results in a compound Zr0.8Cr0.2O2 with an average 5 nm crystallite size of a stabilized cubic (c)-ZrO2-type phase (after 2 h annealing at 773 K in air). A broad Raman band is observed at ~300 cm-1 in acoustic and transverse optic phonons characteristic of the c-ZrO2-type structure, with a prominent O–Cr–O stretching band at 878 cm-1 in a ferromagnetic order. A CrO2/Cr2O3 surface layer exhibits two weak bands at ~1011 cm-1 and 1032 cm-1. The sample exhibits an ‘S’-shaped ferromagnetic hysteresis loop (does not saturate below 60 kOe fields) at 5 K, with a magnetization M = 85.79 emu/g (in the CrO2 part) at 60 kOe and coercivity Hc = 100 Oe. With warming above 5 K, the loop converges progressively with only a weak ferromagnetism at room temperature, M = 9.08 emu/g and Hc = 54.2 Oe. As a pinning barrier, the uncompensated spins in the surface layer supports coercivity at low temperature. A model magnetic structure describes the magnetic properties in correlation to the microstructure.

Structure, conduction mechanisms and multiferroic properties of (Sm, Cr) co-doped Bi0.89Sm0.11Fe0.97Cr0.03O3–NiFe2O4 composition thin films

(Sm, Cr) co-doped Bi0.89Sm0.11Fe0.97 Cr0.03O3 (BSFC)–NiFe2O4 (NFO) composition thin films were successfully prepared on FTO/glass (SnO2:F) substrates via a sol–gel method. The structure, surface morphology, leakage current, ferroelectricity and ferromagnetism of BSFC–NFO composition thin film have been investigated. X-ray diffraction analysis indicates that the thin film is polycrystalline and consisted of a rhombohedral perovskite (R3m space group) BiFeO3 phase and a cubic (Fd-3m space group) inverse spinel NiFe2O4 phase. The BSFC–NFO composition thin film is promising in practical application because of its well saturated ferromagnetic (Ms = 19.45 emu/cm3) and ferroelectric (Pr = 39 µC/cm2) hysteresis loops with low order of leakage current density (J = 6.73 × 10−6 A/cm2, at an applied electric field of 100 kV/cm). Which suggest the ferroelectric and ferromagnetic properties can be improved by this composition thin film structure. Moreover, the various conduction mechanisms of BSFC–NFO composition thin film have also been studied.