10-kOe Field Research Articles

Improved exchange bias and blocking temperature of PtCr/PtMn bilayer antiferromagnets

Herein, we investigated exchange coupling in PtCr/CoFe, PtCr/PtMn/CoFe, and PtMn/CoFe film structures, demonstrating that Pt51Cr49(30 nm)/Co90Fe10(10 nm), Pt51Cr49(27.2 nm)/Pt50Mn50/(2.8 nm)/Co90Fe10(10 nm), and Pt50Mn50(30 nm)/Co90Fe10(10 nm) structures annealed at 350 °C for 20 h in a 10-kOe field featured unidirectional anisotropy constants (Jk) of 0.09, 0.56, and 0.32 erg/cm2, respectively. In the case of the Ni50Fe12Cr38(4 nm)/Pt51Cr49(30 − X nm)/Pt50Mn50(X nm)/Co90Fe10(10 nm)/Ta(10 nm) [X = 0–30 nm] film system, Jk linearly and steeply increased with increasing X to reach a maximum of 0.56 erg/cm2 at X = 2.8 nm and then decreased in a complicated nonlinear fashion as X further increased to 30 nm. On the other hand, the blocking temperature of Pt51Cr49(28 nm)/Pt50Mn50/(2 nm)/Co90Fe10(10 nm) was determined as 500 °C and nearly equaled that of Pt51Cr49(30 nm)/Co90Fe10(10 nm), significantly exceeding the value of 400 °C determined for Pt50Mn50(30 nm)/Co90Fe10(10 nm). These results imply that the exchange bias field of the Ni50Fe12Cr38(4 nm)/Pt51Cr49(30 − X nm)/Pt50Mn50/(X nm)/Co90Fe10(10 nm)/Ta(10 nm) system is ultimately determined by the chemical composition and the modification of the antiferromagnetic spin structure at the ferromagnet–antiferromagnet interface, while the blocking temperature is almost entirely determined by the volume fraction of the PtCr component.

Tuning magnetic properties of BiFeO3 thin films by controlling Mn doping concentration

Mn-doped BiFeO3 (BiFe1–xMnxO3, x = 0, 0.03, 0.05, 0.10, 0.15 and 0.20) polycrystalline multiferroic thin films were successfully synthesized using the facile sol-gel spin-coating method. The crystal structures, surface features, elements valences, and magnetic properties of as-prepared samples were systematically explored. X-ray diffraction and Raman spectroscopy studies revealed the substitutions of Mn into the Fe site and a rhombohedral-to-orthorhombic phase transition. The Field Emission Scanning Electron Microscopy showed a decrease in the average particle sizes and an improvement of surface morphology with increasing the concentration of the substitutes. Energy-dispersive X-ray spectroscopy confirmed the doping concentration of Mn2+ in the samples. X-ray photoelectron spectroscopy indicated the co-existence of Mn2+/Mn3+ ions in the doped films. The remnant magnetization value of BiFe0.90Mn0.10O3 thin film was found to be approximately six times than that of pure BiFeO3 thin film under a magnetic field of 10kOe. The enhanced magnetic property of BiFe0.90Mn0.10O3 thin film was mainly ascribed to the structural distortion of spin cycloid and the enhancement of super-exchange interaction between the Fe3+ (Mn2+) and O2- ions.

Multiferroic and magnetoelectric properties of Pb0.99[Zr0.45Ti0.47(Ni1/3Sb2/3)0.08]O3–CoFe2O4 multilayer composites fabricated by tape casting

A 2-2 type multiferroic composite device encompassing three CoFe2O4 (CFO) layers confined between four Pb0.99[Zr0.45Ti0.47(Ni1/3Sb2/3)0.08]O3 (PZT) layers was fabricated by tape casting. X-ray diffraction data showed good chemical compatibility between the two phases, whereas Scanning Electron Microscopy imaging also revealed an intimate contact between CFO and PZT layers. Under an applied electric field of 65kV/cm, this multilayer device shows a saturated polarisation of 7.5μC/cm2 and a strain of 0.12%, whereas under a magnetic field of 10kOe it exhibits a typical ferromagnetic response and a magnetic moment of 33 emu/g. This device can be electrically poled, after which it exhibits magnetoelectric coupling.

Magnetostriction and spin reorientation studies on [formula omitted] (x = 0, 0.12, 0.2, 0.24, 0.32, 0.36) compounds

Polycrystalline Sm0.9-xNdxPr0.1Fe1.93 (x=0, 0.12, 0.2, 0.24, 0.32 and 0.36) intermetallic compounds were found to stabilize in MgCu2-type cubic Laves phase structure. The easy direction of magnetization (EMD) was seen to be along 〈111〉 direction, accompanied by a rhombohedral distortion in all the compounds, at room temperature. The spin reorientation temperatures were observed at 59K (TSR1) and 190K (TSR2) from the temperature dependent magnetization studies. The spin reorientation temperature (TSR2) was due to the change of EMD from 〈011〉 to 〈111〉. The order–disorder transition (Curie temperature: TC) was found to decrease with increasing Nd content. The anisotropy compensated Sm0.9Pr0.1Fe1.93 compound was found to exhibit the largest induced magnetostriction (λ‖-λ⊥) value of -1822×10-6, from the present studies, at an applied field of 10kOe.

Temperature span of magnetocaloric effect in Nb-doped La0.7Ca0.3Mn1−xNbxO3 (x=0, 0.002 and 0.01)

In this work, we report magnetocaloric effect of Nb-doped on La0.7Ca0.3Mn1-xNbxO3 (x=0, 0.002 and 0.01). Maximum magnetic entropy change under applied field of 10kOe obtained was –ΔSM max of 4.69Jkg−1K−1, 1.75Jkg−1K−1 and 1.95Jkg−1K−1 for x=0.0, 0.002 and 0.01, respectively. Total temperature span of both Nb-doped samples was 51K. A slight Nb-doped obtained a temperature span that went through the temperature span of the sample without Nb-doped, meanwhile more increasing Nb-doped might cause a little enhancement of maximum magnetic entropy change.

Giant magnetic coercivity in YNi4B-type SmNi3TB (T=Mn–Cu) solid solutions

The effects of transition metal substitution for Ni on the magnetic properties of the YNi4B-type SmNi4B via SmNi3TB (T=Mn, Fe, Co, Cu) solid solutions have been investigated. SmNi4B, SmNi3MnB, SmNi3FeB, SmNi3CoB and SmNi3CuB show ferromagnetic ordering at 40K, 210K, 322K, 90K and 57K and field sensitive metamagnetic-like transitions at 15K, 100K, 185K, 55K and 15K in a magnetic field of 10kOe, respectively. The magnetocaloric effects of SmNi3TB (T=Mn–Cu) were calculated in terms of isothermal magnetic entropy change (ΔSm). The magnetic entropy ΔSm reaches value of –0.94J/kgK at 40K for SmNi4B, –1.5J/kgK at 205K for SmNi3MnB, –0.54J/kgK at 320K for SmNi3FeB, –0.49J/kgK at 90K for SmNi3CoB and –0.54J/kgK at 60K for SmNi3CuB in field change of 0–50kOe around the Curie temperature. They show positive ΔSm of +0.71J/kgK at ~10K for SmNi4B, +1.69J/kgK at 30K for SmNi3MnB, +0.89J/kgK at 110K for SmNi3FeB, +1.08J/kgK at 25K for SmNi3CoB and +1.12J/kgK at 10K for SmNi3CuB in field change of 0–50kOe around the low temperature metamagnetic-like transition. Below the field induced transition temperature (change of magnetic structure), SmNi3TB (T=Mn–Cu) exhibits giant magnetic coercivity of 74kOe at 5K for SmNi4B, 69kOe at 20K (90kOe at 10K) for SmNi3MnB, 77kOe at 60K for SmNi3FeB, 88kOe at 20K for SmNi3CoB and 52kOe at 5K for SmNi3CuB.

Structural and Magnetic Properties of Flux-Free Large FeTe Single Crystal

We report synthesis of non superconducting parent compound of iron chalcogenide, i.e., FeTe single crystal by self flux method. The FeTe single crystal is crystallized in tetragonal structure with the P4/nmm space group. The detailed SEM (scanning electron microscopy) results showed that the crystals are formed in slab like morphology and are near (slight deficiency of Te) stoichiometric with homogenous distribution of Fe and Te. The coupled structural and magnetic phase transition is seen at around 70K in both electrical resistivity and magnetization measurements, which is hysteric (deltaT = 5K) in nature with cooling and warming cycles. Magnetic susceptibility (chi-T) measurements showed the magnetic transition to be of antiferromagnetic nature, which is substantiated by isothermal magnetization (M-H) plots as well. The temperature dependent electrical resistivity measured in 10kOe field in both in plane and out of plane field directions showed that the hysteric width nearly becomes double to deltaT = 10K, and is maximum for the out of plane field direction for the studied FeTe single crystal. We also obtained a sharp spike like peak in heat capacity Cp(T) measurement due to the coupled structural and magnetic order phase transitions.

Anomalous magnetic properties of Tb/Cr multilayer

We report the magnetic properties of [Tb/Cr]8 multilayer in which the Curie temperature(TC)of ferromagnetic Tb is much lower than the Néel temperature (TN) of antiferromagnetic Cr. An unexpected coercivity enhancement is observed at temperature above TN. Furthermore, the magnetic hysteresis loops measured after cooling in an applied field of 10kOe exhibit “double hysteresis loops” behaviors at 156–216K. The abnormal temperature dependence of coercivity is correlated with the spin-density wave structure of Cr, the competition between ferromagnetic and antiferromagnetic coupling at the interface of Tb and Cr layers as well as the interlayer coupling of the adjacent Tb layers.

Theoretical investigation of the magnetocaloric effect on La0.7(Ba, Sr)0.3Mn0.9Ga0.1O3 compound at room temperature

Based on a phenomenological model, the magnetic and magnetocaloric properties of La0.7(Ba, Sr)0.3Mn0.9Ga0.1O3 oxide have been studied. Indeed, the magnetic measurements have demonstrated that the sample exhibits a ferromagnetic–paramagnetic transition at room temperature. The value of the magnetocaloric effect such as magnetic entropy change, full width at half-maximum, relative cooling power and magnetic specific heat change has been determined from the calculation of magnetization as a function of temperature under different external magnetic fields. The maximum magnetic entropy change (−ΔSMmax) and the relative cooling power (RCP) are, respectively, 0.57Jkg−1K−1 and 28.68Jkg−1 for a 10kOe field change at 300K, which are the characteristics of a good magnetocaloric material. Hence, the La0.7(Ba, Sr)0.3Mn0.9Ga0.1O3 compound can be considered as a promising material in magnetic refrigeration technology.According to the master curve behavior for the temperature dependence of ΔSM predicted for different maximum fields, this work has confirmed that the paramagnetic–ferromagnetic phase transition observed for our sample is of a second order.

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.

Magnetocaloric effect of Mn5+xGe3−x alloys

Magnetic properties and magnetocaloric effect (MCE) of off-stoichiometric Mn5+xGe3−x (x=−0.1 and 0.3) were studied. Depletion of Mn (x=−0.1) decreased the magnetic moment of the compound due to the reduction of the ferromagnetic Mn–Mn interactions. Mn5.1Ge2.9 appeared to be near the optimal composition since Mn5.1Ge2.9 exhibited increase in the magnetic moment compared to the stoichiometric compound and further Mn-enrichment beyond x=0.1 led to the formation of the weakly magnetic secondary phase. Mn5.1Ge2.9 produced the maximum entropy change of 2.9Jkg−1K−1 at 296K and the refrigeration capacity of 44.5Jkg−1 with an applied field of 10kOe, making Mn5.1Ge2.9 a possible candidate magnetic refrigerant with reasonably high magnetic entropy change and negligible hysteresis.

Modeling and Effects of In Situ Magnetization of Isotropic Ferrite Magnet Motors

This paper outlines a method using finite-element analysis (FEA) to model the magnetization process of a small brushless surface-magnet three-phase motor with isotropic ferrite magnets and concentrated windings. This is aimed at allowing in situ magnetization using the three-phase machine winding. Radial magnetization is the nominal manufactured magnetization pattern; however, the in situ method leads to a variation in the magnetization pattern, and the performance is examined using open-circuit simulations. The properties of the magnet material (a ferrite 5 type) are examined in order to simulate the magnetization. Bulk magnetization Hs-sat levels for ferrite type 5 indicate that a 10-kOe field is required. In this paper, localized magnetization is examined using FEA, and it is measured in actual rotors by examination of the surface flux density when removed from the stator. Methods for deriving the approximate back electromotive force from both the FEA and the surface measurements are put forward; these show a reasonable correlation. The use of magnetization functions allows the magnetization pattern to be applied to the simulations. This paper uses a standard manufactured machine to carry these out. Open-circuit experiments are conducted to validate the presented method.

Role of oxygen concentration on ferromagnetism and electronic transport properties of Co0.53Ti0.47Oδ nanocomposite films

Surface morphology, microstructure, magnetic and transport properties of nonuniform Co0.53Ti0.47Oδ nanocomposite films fabricated by reactive cosputtering have been investigated. We change the oxygen partial pressure (PO) to modulate the oxygen concentration in the films. The average surface roughness first decreases, and then increases with the increase of PO. The films are composed of Co0, Co2+, Ti3+, Ti4+ and O2− ions, and small metal Co grains appear. The saturation magnetization of the films decreases with the increase of PO, which can be ascribed to the antiferromagnetic superexchange interaction between Co2+–O2−Co2+ since the number of Co2+–O2−Co2+ may increase with the increased PO. The resistivity of the samples decreases with the increase of temperature, showing a semiconducting mechanism. The room-temperature resistivity increases with PO, following a relation of logρ=AlogPO. Magnetoresistance (MR) of the films saturated at a field of 10kOe, and varies with the measuring temperature with a relation of logMR=ClogT, where at PO<2.5% MR increases, but at PO⩾2.5% MR decreases with the increase of temperature.

Magnetic properties of NiMn2O4−δ (nickel manganite): Multiple magnetic phase transitions and exchange bias effect

We present magnetic properties of NiMn2O4−δ (nickel manganite) which was synthesized by complex polymerization synthesis method followed by successive heat treatment and final calcinations in air at 1200°C. The sample was characterized by using X-ray powder diffractometer (XRPD), scanning electron microscopy (SEM), field-emission scanning electron microscopy (FE-SEM) and superconducting quantum interference device (SQUID) magnetometer. The XRPD and FE-SEM studies revealed NiMn2O4−δ phase and good crystallinity of particles. No other impurities have been observed by XRPD. The magnetic properties of the sample have been studied by measuring the temperature and field dependence of magnetization. Magnetic measurements of M(T) reveal rather complex magnetic properties and multiple magnetic phase transitions. We show three magnetic phase transitions with transition temperatures at TM1=35K (long-range antiferromagnetic transition), TM2=101K (antiferromagnetic-type transition) and TM3=120K (ferromagnetic-like transition). We found that the TM1 transition is strongly dependent on the strength of the applied magnetic field (TM1 decreases with increasing applied field) whereas the TM3 is field independent. Otherwise, the TM2 maximum almost disappears in higher applied magnetic fields (H=1kOe and 10kOe). Magnetic measurements of M(H) show hysteretic behavior below TM3. Moreover, hysteresis properties measured after cooling of the sample in magnetic field of 10kOe show exchange bias effect with an exchange bias field |HEB|=196Oe. In summary, the properties that distinguish the investigated NiMn2O4-δ sample from other bulk, thin film, ceramic and nanoparticle NiMn2O4-δ systems are the triple magnetic transitions with sharp increase of the ZFC and FC magnetizations at 120K and the exchange bias effect. The analysis of the results and comparison with literature data allowed us to conjecture that the mixed oxidation states of Mn ions, ferromagnetic and antiferromagnetic sublattice orders and surface effects in the sample tailor these interesting magnetic properties.

Effects of heat treatment on the characteristics of mechano-thermally synthesized nano-structured La0.8Ba0.2MnO3 powder

In this study, barium-doped lanthanum manganite, La0.8Ba0.2MnO3 was synthesized via a mechano-thermal route employing high energy ball milling followed by heat treatment. The structural evolution, morphology and thermal behavior of the powders were evaluated using X-ray diffraction, high resolution scanning electron microscope, and differential thermal analysis/thermo-gravimetric analysis, respectively. The magnetic properties were investigated using an AC susceptometer. X-ray diffraction results revealed the formation of a single phase La0.8Ba0.2MnO3 perovskite with a mean crystallite size of 13nm in a 30h milled sample after the heat treatment at 700°C for 1h. The images of the high resolution scanning electron microscope showed the mean particle size of 350nm for 5h heat treated sample at 1200°C and a change from round-type to multifaceted morphology by increasing the heat treatment temperature. AC susceptibility results showed that increasing heat treatment temperature and time to 1300°C and 5h, respectively, leads to 60% increase in Curie temperature. The paramagnetic–ferromagnetic transition width decreases by increasing the heat treatment temperature and time. The samples heat treated at 900 and 1100°C for 1h exhibited reentered spin-glass behavior which is probably because of the deficiency of Ba content. The milled sample after the heat treatment at 1300°C exhibits metal–insulator behavior and metal–insulator transition temperature (TM–I) is highly dependent on the applied magnetic field. The maximum TM–I shifts from 230K at zero magnetic field towards room temperature near 244K with applying the external magnetic field of 10kOe. It was found that the milled sample after heat treatment at 1300°C exhibits the high MR of 18% at 300K under H=10kOe. This exceptional MR at room temperature suggests this material as a most promising nano-structured CMR material.

High frequency AC response, DC resistivity and magnetic studies of holmium substituted Ni-ferrite: A novel electromagnetic material

Nanoparticles of holmium substituted nickel ferrites (NiHoxFe2−xO4) with x ranging from 0.0 to 0.15 have been prepared by the sol–gel auto-combustion method. Structural and morphology studies have been performed by X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). XRD patterns revealed the formation of pure spinel phase ferrites without any impurity phase. Lattice parameter increases along with a decrease in crystallite size with increasing the concentration of Ho3+ in the parent nickel ferrite due to large ionic radius of Ho3+ (0.901Å) as compared to Fe3+ (0.67Å). SEM shows the spherical, uniformly distributed homogenous nanoparticles grown by controlled reaction parameters of the sol–gel method. Complex permittivity (ε*) and complex electric modulus (M*) have been studied for the present nanoferrites in the frequency ranges of 1MHz–1GHz. Frequency dependent dielectric parameters (relative permittivity (ε′), dielectric loss (ε″), dielectric loss tangent (tanδ)) decreases due to holmium substitution in nickel ferrites, showing the electrical conduction is decreasing in the nickel holmium ferrites with increase in the concentration of holmium. Complex modulus plots shows the poorly resolved semi circles and relaxation of nanoferrite is studied in the high frequency region. Also the relaxation time increases due to increase in x (0.0–0.15). DC electrical resistivity increases (107Ω-cm–1010Ω-cm) due to holmium ions substitution in nickel ferrites. Magnetic behavior was also characterized using a Vibrating Sample Magnetometer (VSM) under an applied magnetic field of 10kOe and shows that magnetization decreases with increase in composition of holmium in nickel ferrites. High frequency behavior, low losses and very high DC electrical resistivity made the material a novel one for electromagnetic devices.

Low temperature synthesis and enhanced electrical properties by substitution of Al3+ and Cr3+ in Co–Ni nanoferrites

Aluminum and chromium substituted Co–Ni spinel nanoferrites were prepared by sol–gel auto combustion method. Structural parameters along with electrical and magnetic properties have been investigated in the present work. Crystallite sizes of nano ferrite estimated from the peak (311) lies in the range of 13–21nm ±2nm and compared with crystallite sizes calculated from Williamsons–Hall plots. DC electrical resistivity variations due to the concentration of aluminum and chromium in the host ferrite have been measured from 368K to 573K. Increase in the room temperature DC electrical resistivity was observed up to a concentration x=0.2 and then decreases for x >0.2. Dielectric parameters (real and imaginary part of complex permittivity, dielectric loss tangent) were studied as a function of frequency (20Hz–5MHz) and a decrease in the dielectric parameters was observed due to substitution of nickel, aluminum and chromium ions in cobalt nanoferrites. AC conductivity, complex impedance and complex electrical modulus were studied as a function of frequency for the conduction and relaxation mechanisms in the present ferrite system. Saturation magnetization, coercivity, canting angles and magneto crystalline anisotropy variations with composition were observed and presented for the present ferrites under an applied magnetic field of 10kOe at room temperature. It was found that both magnetization and coercivity decreases with increase in the concentration of aluminum and chromium along with a decrease in the anisotropy parameters. High DC resistivity with low dielectric parameters of the present nanoferrites make them suitable for high frequency and electromagnetic wave absorbing devices.

The magnetocaloric effect in Gd3In1−xAlx (x=0, 0.04, 0.08) alloys

The crystal structure and magnetic phase transition were investigated for, Gd3In1−xAlx (x=0, 0.04, 0.08) alloys. All these samples crystallize in the Gd3Co-type orthorhombic structure at room temperature. A second-order magnetic phase transition occurs around the Curie temperature of 192K in Gd3In alloy. With the substitution of Al for In, the magnetic anisotropy decreases obviously in Gd3In1−xAlx alloys. Relatively large and highly reversible magnetocaloric effects were obtained under the low field of 10kOe, suggesting that Gd3In1−xAlx alloys are potential candidates for magnetic refrigeration at low temperatures.

Fabrication and characterization of ferrimagnetic bioactive glass-ceramic containing BaFe12O19

Bioactivity of ferrimagnetic glass-ceramics is useful as thermo seeds for hyperthermia treatment of cancer. Ferrimagnetic glass-ceramics were prepared from the BaFe12O19(BF)–SiO2–CaO–Na2O–P2O5 system using the incorporation method. The mixture was then further sintered at 800 °C to form the glass-ceramic samples. The structure and microstructure of the samples were characterized by X-ray diffraction, energy dispersive X-ray analysis (EDXA) and scanning electron microscopy. Magnetic hysteresis loops of the glass-ceramic samples were obtained with maximum field of 10kOe, in order to evaluate the potential of these samples for hyperthermia treatment of cancer. In vitro bioactivity was investigated in simulated body fluid (SBF) for 14 days. The results showed that Na2Ca2Si3O9 and BaFe12O19 were the main phases in the glass-ceramic samples. Apatite was formed on the surface layers of the glass-ceramics, confirming their biocompatibility. It was found that the bioactivity increased with an increase in BF contents.

Magnetodielectric effect in composites of nanodimensional glass and CuO nanoparticles

Nanocomposites comprising CuO particles of average diameter 21nm coated with 5nm silica glass containing iron ions were synthesized by a chemical route. An ion exchange reaction at the nanoglass/CuO interface produced iron-doped CuO with copper ion vacancies within the nanoparticles. Room temperature ferromagnetic-like behavior was observed in the nanocomposites. This was ascribed to uncompensated spins contributed by Fe ions with associated copper ion vacancies. A rather high value of magnetodielectric parameter in the range 16–26% depending on the measuring frequency was exhibited by these nanocomposites at a magnetic field of 10KOe. This was caused by a magnetoresistance of 33% in the iron doped CuO nanoparticles. The experimental results were fitted to the Maxwell–Wagner Capacitor model developed by Catalan. These materials will be suited for magnetic sensor applications.