Ferromagnetic Hysteresis Loops Research Articles

Particle size effect on the magnetic properties of NiO nanoparticles prepared by a precipitation method

Nickel oxide (NiO) nanoparticles of nominal size range 16 nm and 25 nm were obtained by controlling the calcination temperature. These particles were prepared by the precipitation method. Structural, optical and morphological characterizations were done by X-ray powder diffraction, UV–vis diffuse reflectance spectroscopy and scanning electron microscopy. Studies of magnetic measurements (up to 60 kOe) and temperature variations from 2 K to 300 K of the NiO nanoparticles were investigated. Particles of 16 nm exhibited a weak ferromagnetic component and hysteresis loop. There is a increase in coercivity H c and the remanence M r at 8 K accompanied by an exchange bias H E. H E monotonically tends to zero as the particles size varied from 16 nm to 25 nm. The hysteresis loop and the size dependent χ are interpreted with the uncompensated surface spins, whereas the transition at 30 K is suggested to be Néel temperature T N of the spins in the core of the 16 nm particles. In addition, the increasing temperature cannot showed an approach to saturation in the magnetization curve, it indicates the possibility of an asperomagnetism and/or spin glass behavior of the NiO nanoparticles.

Ubiquity of ferromagnetic signals in common diamagnetic oxide crystals

The magnetic properties of MgO, ${\text{MgAl}}_{2}{\text{O}}_{4}$, ${\text{SrTiO}}_{3}$, ${\text{LaAlO}}_{3}$, LSAT, and ZnO single crystals were investigated. These crystals show three contributions to the magnetization, namely, an intrinsic diamagnetic contribution, a paramagnetic contribution, due to various transition-metal impurities, as well as a ferromagnetic contribution. The latter shows coercive field values that are rather independent of the actual crystal material. The ferromagnetic hysteresis loops of the magnetization per volume suggest a surface contribution. The origin of the ferromagnetic contribution as arising from either defect-induced ferromagnetism or ferromagnetic impurities is discussed.

Multiferroic Bi 0.7Dy 0.3FeO 3 thin films directly integrated on Si for integrated circuit compatible devices

Magnetoelectric multiferroic Bi 0.7Dy 0.3FeO 3 (BDFO) thin films deposited on p-type Si (100) substrate using pulsed laser deposition technique demonstrated a saturated ferroelectric and ferromagnetic hysteresis loop at room temperature. More interestingly, the observed change in electric polarization with applied magnetic field in these films indicated the presence of room temperature magnetoelectric coupling behavior. Using high-frequency capacitance–voltage measurements, the fixed oxide charge density, interface trap density and dielectric constant were estimated on Au/BDFO/Si capacitors. These results suggest the integrated circuit compatible application potential of BDFO films in the field of micro-electro-mechanical systems and non-volatile memories.

Self-Formed Exchange Bias of Switchable Conducting Filaments in NiO Resistive Random Access Memory Capacitors

We report on the ferromagnetism of conducting filaments formed in a NiO thin film, which exhibited a typical bistable resistive switching characteristic. The NiO thin film showed an antiferromagnetic hysteresis loop for a high resistive state (R(OFF)). However, for a low resistive state (R(ON)), the conducting filaments exhibited a ferromagnetic hysteresis loop for the field cooling. The ferromagnetic hysteresis behavior of the R(ON) state reveals switchable exchange coupling between the ferromagnetic Ni conducting filaments and the antiferromagnetic NiO layer.

Enlarged ferromagnetic hysteresis in InMnP:Be epilayers formed by thermal diffusion using MBE-grown Mn/InP:Be bilayers

The p-type InMnP:Be epilayers, which were prepared by thermal diffusion of Mn through in-situ deposition of Mn layer using molecular beam epitaxy (MBE) onto MBE-grown InP:Be epilayers and subsequent in-situ annealing at 300–350 °C, were investigated. InMnP:Be epilayers prepared by the above sequence clearly showed the Mn-related emission band at 1.1–1.2 eV, which indicates the effective incorporation of Mn 2+ ions into the host layer InP:Be. The samples demonstrated very large ferromagnetic hysteresis loops with enhanced coercivity, and the ferromagnetic-to-paramagnetic transition of the samples was observed to occur at ∼85 K. These results suggest that InP-based ferromagnetic semiconductor layers having enhanced ferromagnetism can be effectively formed by the above-mentioned sequential in-situ processes.

Quantum criticality in CePt1−xNix due to hydrostatic and chemical pressure

AbstractWe have investigated the possibility of tuning ferromagnetic CePt1−xNix for $x = 0.85$ and 0.9 to a quantum critical point (QCP) by measuring the magnetization between 2 and 300 K on polycrystals under pressures up to 13 kbar. Thus we constructed a TC–p phase diagram for CePt1−xNix with $x = 0.85$. For the alloy with $x = 0.9$ we show that the ferromagnetic hysteresis loop at 2.5 K is completely suppressed by a hydrostatic pressure of 10.2 kbar. Our findings suggest that Ce(Pt:Ni) can be tuned to the QCP with the application of hydrostatic pressure at considerably lower pressures than pure CePt.

Room-temperature magnetoelectric coupling in Bi4(Ti1Fe2)O12−δ system

Bi4(Ti1Fe2)O12−δ ceramics were prepared by the conventional solid state reaction method. The sample exhibited ferroelectricity and magnetism simultaneously at room temperature, which was demonstrated by the ferroelectric (2Pr = 4.1 µC cm−2, 2Ec = 42 kV cm−1 at applied electric field 31 kV cm−1) and ferromagnetic (Mr = 3 × 10−3 emu g−1, Hc = 218 Oe) hysteresis loops. Changes of 19.7% and 17.1% in, respectively, remanent polarization and magnetization after poling the sample in magnetic and dc electric for fields 10 min were evidence of magnetoelectric coupling between the electric dipoles and magnetic dipoles at room temperature.

Enhanced ferromagnetism in H2O2-treated p-(Zn0.93Mn0.07)O layer

Enhanced ferromagnetism was observed from the H2O2-treated p-type (Zn0.93Mn0.07)O:As layer. Compared with the untreated sample, the H2O2-treated sample showed the enlarged ferromagnetic hysteresis loop with approximately two-times-increased spontaneous magnetization. And also, in comparison with the untreated sample (TC∼280 K), the H2O2-treated sample exhibited to have the increased TC persisting up to above 350 K. These results were confirmed to originate from the enhanced p-d hybridization due to the decrease in negatively charged residual background carriers. This is because the increased effective g-factor resulting from the decrease in oxygen-related defects acting as native deep donors was observed from the H2O2-treated sample.

Theoretical and experimental evidence of enhanced ferromagnetism in Ba and Mn cosubstituted BiFeO3

Ba and Mn doped BiFeO3 prepared through the pyrolysis of xerogel precursors are characterized by powder x-ray diffraction, high resolution transmission electron microscopy, superconducting quantum interference device magnetometry, and polarization measurements. Structural studies by x-ray diffraction and transmission electron microscopy show a tetragonal lattice for Ba substituted BiFeO3 and a rhombohedral lattice for Mn substituted BiFeO3. A large ferromagnetic hysteresis loop is observed for Ba doped BiFeO3. Coexistence of distorted rhombohedral and tetragonal phases is observed in Ba and Mn codoped BiFeO3, where enhanced ferroelectric and ferromagnetic properties are produced by the internal strain. Density functional calculations are used to substantiate the results.

Multiferroic Properties of Highly c-Oriented BiFeO[sub 3] Thin Films on Glass Substrates

BiFeO 3 (BFO) thin films were deposited on SrRuO 3 (SRO)/yttria-stabilized zirconia (YSZ)/glass substrates by pulsed laser deposition. To grow highly a- and (110)-oriented SRO bottom electrodes, we used YSZ buffer layers between SRO bottom electrodes and glass substrates. On the highly a- and (110)-oriented SRO bottom electrodes, we obtained highly c- and (011)-oriented BFO thin films in which the structures of BFO thin films were confirmed by X-ray diffraction experiments. The highly c-oriented BFO thin film exhibited a higher ferroelectric polarization (about 40 μC/cm 2 ) than the highly (011)-oriented BFO thin film. The highly c-oriented BFO thin film also showed a ferromagnetic hysteresis loop while the highly (011)-oriented BFO thin film exhibited a superparamagnetic hysteresis loop.

Magnetic and ferroelectric properties of epitaxial Sr-doped [formula omitted] thin films

We investigate the magnetic and ferroelectric properties of epitaxial Sr-doped BiFeO 3, i.e., Bi 0.75Sr 0.25FeO 3−δ, thin films prepared by pulsed laser deposition. The films deposited at high oxygen pressure show a ferroelectric hysteresis loop at room temperature with remnant polarization of 2 P r = 86.13 μ C / cm 2 and coercive field of 2 E C = 75.5 kV / cm . Compared with the epitaxial BiFeO 3 thin film, the remnant polarization and coercive field of Bi 0.75Sr 0.25FeO 3−δ are small, probably due to the dilution of Bi 3+ ions, the existence of oxygen vacancies, and a small domain size. On the contrary, the films deposited at low oxygen pressure show a ferromagnetic hysteresis loop at room temperature. However, x-ray absorption and x-ray magnetic circular dichroism measurements show that the observed magnetic moment might be related to the formation of a γ - Fe 2O 3 impurity phase.

Magnetocapacitance in BaTiO 3–CoFe 2O 4 nanocomposites

We report on the magnetoelectric characterization of epitaxial CoFe 2O 4–BaTiO 3 nanocomposites grown by rf sputtering on Nb-doped SrTiO 3 (001). Multiferroicity of the material is corroborated with both, ferroelectric and ferromagnetic hysteresis loops. Magnetoelectric coupling is investigated via magnetocapacitance measurements; a change of the capacitance of about 2% is observed for an applied magnetic field of 8 T. The possible origins of this magnetocapacitance are discussed.

Ferromagnetic modification of GaN film by Cu + ions implantation

The structural and magnetic properties of Cu + ions-implanted GaN films have been reported. Eighty kiloelectron-volt Cu + ions were implanted into n-type GaN film at room temperature with fluences ranging from 1 × 10 16 to 8 × 10 16 cm −2 and subsequently annealed at 800 °C for 1 h in N 2 ambient. PIXE was employed to determine the Cu-implanted content. The magnetic property was measured by the Quantum Design MPMS SQUID magnetometer. No secondary phases or clusters were detected within the sensitivity of XRD. Raman spectrum measurement showed that the Cu ions incorporated into the crystal lattice positions of GaN through substitution of Ga atoms. Apparent ferromagnetic hysteresis loops measured at 10 K were presented. The experimental result showed that the ferromagnetic signal strongly increased with Cu-implanted fluence from 1 × 10 16 to 8 × 10 16 cm −2.

Structural and magnetic properties of electrodeposited Cobalt nanowire arrays

Ordered magnetic nanowires have tremendous potential in future magnetic storage and high frequency magnetic logic devices. Here, we present the fabrication of ordered arrays of Cobalt nanowires by electrodeposition through porous polycarbonate membranes. Vertically and horizontally aligned nanowires were produced in presence of an external bias field during post deposition etching of the polycarbonate membrane. Structural and compositional analyses have been carried out to establish the material and structural purity. The magneto-optical Kerr effect was employed to measure the magnetic hysteresis loops for the nanowires assembled in the substrate plane. A good magneto-optical signal to noise ratio is observed with clean ferromagnetic hysteresis loops. The loops measured with external magnetic field applied parallel and perpendicular to the axis of the nanowires show a clear difference in the shape and the coercive field, indicating the effect of shape anisotropy in these samples. Micromagnetic simulations were performed to understand the experimental results and to obtain insight to the magnetization reversal mechanism in magnetic nanowires.

Synthesis of nanocrystalline YFeO 3 and its magnetic properties

Single phase nanocrystalline YFeO 3 has been synthesized by a simple solution method. The average particle diameter is 42.2 nm. The particles exhibit ferromagnetic behaviour in the temperature range 10–300 K with a coercivity of 23 kOe. The magnetization versus temperature over the temperature range 2–300 K obeys Bloch equation with a Bloch constant value 9.98×10 −6 K −3/2. Ferromagnetic hysteresis loops have been observed up to a temperature of 300 K. At 10 K a field-cooled sample shows an exchange bias field.

Room-Temperature Ferromagnetic Property in MnTe Semiconductor Thin Film Grown by Molecular Beam Epitaxy

MnTe layers of high crystalline quality were successfully grown on Si(111) and Al2O3(0001) substrates by molecular beam epitaxy. We have investigated the structure, magnetic and electric transport properties of MnTe layers by using X-ray diffraction (XRD), superconducting quantum interference device (SQUID) magnetometer, physical properties measurement system (PPMS), and X-ray photoelectron spectroscopy (XPS). Characterization of MnTe layers on Si(111) and Al2O3(0001) substrates by X-ray diffraction (XRD) revealed a hexagonal structure of polycrystalline growth for MnTe/Si(111) and epitaxial growth for MnTe/Al2O3 (0001), respectively. Investigation of magnetic properties for MnTe layers showed ferromagnetic properties above room temperature unlike antiferromagnetic bulk MnTe materials. The great irreversibility between zero-field-cooling and field-cooling magnetization were observed. Apparent ferromagnetic hysteresis loops are measured at room temperature. In electro-transport measurements, the temperature dependence of resistivity revealed a noticeable semiconducting behaviors and showed a conduction via variable range hopping (VRH) at low temperature. From XPS results, we assume that the origin of ferromagnetism in samples may be due to the breaking of superexchange antiferromagnetic correlations between Mn spin moments arising from Tellurium vacancies.

Reproducible manipulation of spin ordering in ZnCoO nanocrystals by hydrogen mediation

Through a simple post hydrogen plasma treatment, we show the strong inducement of the room temperature ferromagnetism in Zn0.9Co0.1O:H nanocrystals fabricated by sol-gel process. X-ray diffraction, high resolution transmission electron microscopy, and neutron high resolution powder diffraction measurements of Zn0.9Co0.1O nanocrystals before and after hydrogenation process confirmed that there are no structural changes in nanocrystal and any creation of magnetic secondary phase. Nevertheless, the clear ferromagnetic hysteresis loop of the hydrogenated Zn0.9Co0.1O nanocrystal was observed in superconducting quantum interference device. These results indicate that the ferromagnetism can be derived from a short-range spin ordering by hydrogen mediation in Co doped ZnO.

Characterizations of n-type ferromagnetic GaMnN thin film grown on GaN/Al 2O 3 (0 0 0 1) by metal-organic chemical vapor deposition

A high-quality ferromagnetic GaMnN (Mn=2.8 at%) film was deposited onto a GaN buffer/Al 2O 3(0 0 0 1) at 885 °C using the metal-organic chemical vapor deposition (MOCVD) process. The GaMnN film shows a highly c-axis-oriented hexagonal wurtzite structure, implying that Mn doping into GaN does not influence the crystallinity of the film. No Mn-related secondary phases were found in the GaMnN film by means of a high-flux X-ray diffraction analysis. The composition profiles of Ga, Mn, and N maintain nearly constant levels in depth profiles of the GaMnN film. The binding energy peak of the Mn 2p 3/2 orbital was observed at 642.3 eV corresponding to the Mn (III) oxidation state of MnN. The presence of metallic Mn clusters (binding energy: 640.9 eV) in the GaMnN film was excluded. A broad yellow emission around 2.2 eV as well as a relatively weak near-band-edge emission at 3.39 eV was observed in a Mn-doped GaN film, while the undoped GaN film only shows a near-band-edge emission at 3.37 eV. The Mn-doped GaN film showed n-type semiconducting characteristics; the electron carrier concentration was 1.2×10 21/cm 3 and the resistivity was 3.9×10 −3 Ω cm. Ferromagnetic hysteresis loops were observed at 300 K with a magnetic field parallel and perpendicular to the ab plane. The zero-field-cooled and field-cooled curves at temperatures ranging from 10 to 350 K strongly indicate that the GaMnN film is ferromagnetic at least up to 350 K. A coercive field of 250 Oe and effective magnetic moment of 0.0003 μ B/Mn were obtained. The n-type semiconducting behavior plays a role in inducing ferromagnetism in the GaMnN film, and the observed ferromagnetism is appropriately explained by a double exchange mechanism.

Ferromagnetism inCo7(TeO3)4Br6: A byproduct of complex antiferromagnetic order and single-ion anisotropy

Pronounced anisotropy of magnetic properties and complex magnetic order of a new oxi-halide compound ${\text{Co}}_{7}{({\text{TeO}}_{3})}_{4}{\text{Br}}_{6}$ has been investigated by powder and single-crystal neutron-diffraction, magnetization, and ac susceptibility techniques. Anisotropy of susceptibility extends far into the paramagnetic temperature range. A principal source of anisotropy are anisotropic properties of the involved octahedrally coordinated single ${\text{Co}}^{2+}$ ions, as confirmed by angular-overlap-model calculations presented in this work. Incommensurate antiferromagnetic order sets in at ${T}_{N}=34\text{ }\text{K}$. The propagation vector is strongly temperature dependent reaching ${\mathbf{k}}_{1}=[0.9458(6),0,0.6026(5)]$ at 30 K. A transition to a ferrimagnetic structure with ${\mathbf{k}}_{2}=0$ takes place at ${T}_{C}=27\text{ }\text{K}$. The magnetically ordered phase is characterized by very unusual anisotropy as well: while $M\text{\ensuremath{-}}H$ scans along the $b$ axis reveal spectacularly rectangular but otherwise standard ferromagnetic hysteresis loops, $M\text{\ensuremath{-}}H$ studies along other two principal axes are perfectly reversible, revealing very sharp spin-flop (or spin-flip) transitions, such as in a standard antiferromagnet (or metamagnet). Altogether, the observed magnetic phenomenology is interpreted as an evidence of competing magnetic interactions permeating the system, in particular of the single-ion anisotropy energy and the exchange interactions. Different coordinations of the ${\text{Co}}^{2+}$ ions involved in the low-symmetry $C2/c$ structure of ${\text{Co}}_{7}{({\text{TeO}}_{3})}_{4}{\text{Br}}_{6}$ render the exchange-interaction network very complex by itself. Temperature-dependent changes in the magnetic structure, together with an abrupt emergence of a ferromagnetic component, are ascribed to continual spin reorientations described by a multicomponent, but yet unknown, spin Hamiltonian.

Ferromagnetism and exchange bias in a diluted magnetic ferroelectric oxide

We report on the observations of room-temperature ferromagnetism and ferroelectricity in the epitaxial thin film of ${\text{BaTi}}_{0.98}{\text{Co}}_{0.02}{\text{O}}_{3}$ (CBTO) with detailed structural and magnetic analyses. The films are single phase with an inhomogeneous distribution of ${\text{Co}}^{2+}$ dopants in the structure. Room-temperature ferromagnetic hysteresis and ferroelectric loop were observed. Remarkably, the hysteresis loops for field cooling show the exchange bias and training effects. The complex magnetic behavior of CBTO was interpreted in the frame of bound magnetic polaron formation with inhomogeneity of dopant distribution. This work also demonstrated that exchange bias can be a helpful technique in exploring the mechanism of dopant-induced ferromagnetism.