Ferrimagnetic Hysteresis Loop Research Articles

Structural, magnetic, and microwave features of Sc3+ ions substituted Sr0.5Ba0.5Fe12O19 nanohexaferrites

In this study, magnetic, structural, and hyperfine interactions of Sc3+ ion substituted Sr0.5Ba0.5Fe12O19 (Sr0.5Ba0.5ScxFe12−xO19 (x ≤ 0.1)) nanohexaferrites (Sc→SrBa NHFs) have synthesized through the sonochemical approach. The structure and morphology were studied by XRD, SEM, HR-TEM, and TEM along with EDX. XRD analysis confirmed the hexaferrite formation having crystallite within the range of 45 to 79 nm. Both TEM, HR-TEM, and SEM analyses proved the hexagonal morphology of all products. All products show ferrimagnetic hysteresis loops at both Ts. The evaluation of M(H) hysteresis loops indicated that the Ms (saturation magnetization), Mr (remanence), Hc (coercivity), and nB(Bohr magneton number) gradually decline with the incorporation of Sc3+ ion. Higher doping contents (x ≥ 0.08) revealed a considerable decline in Mr and Hc, showing significant changes from hard to soft magnetic behavior at higher contents. Mössbauer spectra show that Sc3+ ions are located at commonly octahedral (Oh) 4 f2 site. It was also determined that a small amount of Sc3+ occupied the 2b site. The microwave features of the products were determined by measuring S-parameters within the 2–10 GHz range. It was presumed that the energy losses resulting from reflection encompass both electrical and magnetic loss components. The average value of the reflection coefficient is − 14.48–14.24 dB. A noteworthy attenuation of the reflected wave energy opens up broad prospects for practical applications as coatings for providing electromagnetic compatibility.

Size dependent structural and magnetic properties of Co(1−x) Nix Cr2O4 nanoparticles (x = 0.15, 0.20)

This study examines the structural and magnetic characteristics of Co(1−x)NixCr2O4 (x = 0.15, 0.20) compounds synthesised using the co-precipitation technique and calcined at 500 °C and 900 °C respectively. X-ray diffraction studies reveal the structure of the synthesized samples is face-centered cubic with space group Fd-3m. The particle sizes and morphology were examined by using transmission electron microscopy, and the size ranges from 64 ± 10 nm to 105 ± 15 nm for the 900 °C and 7 ± 2 and 8 ± 2 nm for the 500 °C calcined samples. Field-cooling and zero-field-cooling magnetization measurement protocols were used to investigate the materials' magnetic characteristics. The Curie temperature (TC) decreases from 91 ± 0.5 K to 85 ± 0.3 K as the Ni concentration increases from x = 0.15–0.20. Additionally, an increase in the TC value is seen for both compositions when the particle size is decreased. Spiral ordering is observed at a transition temperature TS for the samples calcined at 900 °C, while no evidence for TS was seen for samples calcined at 500 °C. Magnetization measurements as a function of field, Mμ0H, at several constant temperatures, show that the coercivity reduces with an increase in temperature in all samples. The Co(1−x)NixCr2O4 (x = 0.15, 0.20) samples calcined at 900 °C exhibit superparamagnetic behaviour with a small ferrimagnetic hysteresis loop. Furthermore, this paper evaluates the contribution of ferrimagnetic, superparamagnetic, and paramagnetic phases to the total Mμ0H curve for Co(1−x)NixCr2O4 (x = 0.15, 0.20) calcined at 900 °C through simulation. In addition, a modified Langevin simulation, incorporating a particle size distribution term, is performed for the Co(1−x)NixCr2O4 (x = 0.15, 0.20) samples calcined at 500 °C. From the simulations, it is clear that all samples show evidence of significant superparamagnetic contributions to the total saturation magnetization because of the small particles present.

Impact of Sc3+/In3+ ions co-substitution on structural, magnetic, and microwave features of SrFe12O19 hexaferrites

ScIn→Sr NHFs have been synthesized via the sol-gel combustion method. The phase and morphonology were analyzed via XRD, SEM, TEM, and HR-TEM. XRD measurements confirmed the purity of all products having the crystallite size (DXRD) of 31–77 nm obtained via Rietveld refinement. The agglomeration of products was observed in SEM and HR-TEM images due to their magnetic character. SEM images revealed the hexagonal-shaped nanoparticles. Mössbauer spectra showed that In3+ and Sc3+ ions are located at generally octahedral (Oh) 4 f2 site. The electron density s of iron ions of 4 f2 and 2a sublattices is affected by doping content. The obtained M-H curves (field-dependence of magnetization) demonstrated ferrimagnetic hysteresis loops at both 300 and 10 K. The analysis of M-H curves also showed that the saturation magnetization (Ms) first declined until x = 0.03, then grew up to x = 0.05, and returned to decrease thereafter. The coercivity (Hc) decreased sharply with Sc-In substitution, transforming the magnetic character of samples from hard to soft. Microwave (MW) properties were measured and analyzed between 33 and 50 GHz. It was demonstrated that the increase of the Sc3+/In3+ concentration led to modifications in amplitude-frequency characteristics of the electromagnetic absorption process. It was shown that Sc3+/In3+ substituted Sr NHFs can be used for developing radioelectronic coatings and providing electromagnetic compatibility.

Magnetization reversal through an antiferromagnetic state

Magnetization reversal in ferro- and ferrimagnets is a well-known archetype of non-equilibrium processes, where the volume fractions of the oppositely magnetized domains vary and perfectly compensate each other at the coercive magnetic field. Here, we report on a fundamentally new pathway for magnetization reversal that is mediated by an antiferromagnetic state. Consequently, an atomic-scale compensation of the magnetization is realized at the coercive field, instead of the mesoscopic or macroscopic domain cancellation in canonical reversal processes. We demonstrate this unusual magnetization reversal on the Zn-doped polar magnet Fe2Mo3O8. Hidden behind the conventional ferrimagnetic hysteresis loop, the surprising emergence of the antiferromagnetic phase at the coercive fields is disclosed by a sharp peak in the field-dependence of the electric polarization. In addition, at the magnetization reversal our THz spectroscopy studies reveal the reappearance of the magnon mode that is only present in the pristine antiferromagnetic state. According to our microscopic calculations, this unusual process is governed by the dominant intralayer coupling, strong easy-axis anisotropy and spin fluctuations, which result in a complex interplay between the ferrimagnetic and antiferromagnetic phases. Such antiferro-state-mediated reversal processes offer novel concepts for magnetization control, and may also emerge for other ferroic orders.

Chemical Vapor Deposition of Ferrimagnetic Fe3O4 Thin Films

Ultrathin magnetic materials with room-temperature ferromagnetism/ferrimagnetism hold great potential in spintronic applications. In this work, we report the successful controllable growth of Fe3O4 thin films using a facile chemical vapor deposition method. Room-temperature ferrimagnetism was maintained in the as-grown Fe3O4 thin films down to 4 nm. Raman spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy analysis were conducted to reveal the structure and quality of the Fe3O4 film. Magnetization measurement showed ferrimagnetic hysteresis loops in all Fe3O4 thin films. A saturation magnetization of 752 emu/cm3 was observed for the 4 nm Fe3O4 film, which was higher than that of bulk Fe3O4 materials (480 emu/cm3). Additionally, the Verwey transition at ~120 K was visible for the Fe3O4 thin films. This work provides an alternative method of synthesizing ferrimagnetic ultrathin films for electronic, spintronic, and memory device applications.

Ground state phase diagrams and hysteresis loop of azulene-like nano-structure: a Monte Carlo study

The magnetic properties and ferrimagnetic hysteresis loop of azulene-like nano-structure have been investigated via Monte Carlo simulations. The ground state phase diagrams of azulene-like nano-structure with half and integer mixed spins (3;3/2) are found. The multiphase points, disordered regions and various structures are presented. Ground state phase diagrams are useful for checking the reliability of the numerical results for temperature phase diagrams and allow to explore regions where significant magnetic behavior could occur. The transition and compensation temperatures are obtained. The temperature dependence of magnetization is established. From the study of magnetic properties in terms of Arrott plots, we deduced that ferrimagnetic phase transition is of second order in our system. The variation of total magnetization, transition and compensation temperatures with crystal field were obtained. The magnetic hysteresis cycles for several temperatures, exchange interactions between S–S and crystal filed DS are determined. The magnetic properties of azulene-like nano-structure were directly related to the ordering magnetic structure. Here, we show first results for such azulene-like nano-structure.

Structural, cation distribution, optical and magnetic properties of quaternary Co0.4+xZn0.6-xFe2O4 (x = 0.0, 0.1 and 0.2) and Li doped quinary Co0.4+xZn0.5-xLi0.1Fe2O4 (x = 0.0, 0.05 and 0.1) nanoferrites

This study explore the influence of 10% Li doping on the crystallography, cation distribution, morphology, optical and magnetic properties of middle range Cobalt–Zinc nanoferrites. Single-phase intrinsic quaternary Co0.4+xZn0.6-xFe2O4 (x = 0.0, 0.1 and 0.2) and 10% Li doped quinary Co0.4+xZn0.5-xLi0.1Fe2O4 (x = 0.0, 0.05 and 0.1) nanoferrites with average crystallite size in the 13–34 nm range were synthesized through sol-gel auto-combustion method. Rietveld profile refinement of the PXRD patterns, presence of fcc rings in the SAED patterns and observation of active Raman modes illustrated single phase formation of mixed spinel nanoferrites in the fcc structure without impurity. In these nanoferrites Zn2+ ions preferentially occupy the tetrahedral site and Co2+ & Li1+ ions occupy the octahedral site with total preference. Both intrinsic quaternary and Li doped quinary nanoferrites significantly absorbs optical light in the UV band. The band gap energy decreases with decreasing Zn concentration and Li doping in these nanoferrite leads to blue shift of more than 1eV in the band gap energy. Co0.4+xZn0.6-xFe2O4 (x = 0.1 and 0.2) and Co0.4+xZn0.5-xLi0.1Fe2O4 (x = 0.0, 0.05 and 0.1) nanoferrites exhibited S-shape ferrimagnetic hysteresis loops at 300 K, 200 K, 100 K & 20 K. The Co0.4Zn0.6Fe2O4 nanoferrite display superparamagnetism at 300 K with a blocking temperature at 183 K. Systematic enhancement in the saturation magnetization (Ms), coercivity (Hc), remanence (Mr) and squareness ratio with lowering the temperature in these nanoferrites revealed conversion of soft-ferrimagnetic to hard-ferrimagnetic character. 10% Li doping in these nanoferrites resulted in significant enhancements of the Hc, Mr and TB. Monotonic increase in the Ms, Hc, Mr and TB has also been observed with the decreasing Zn concentration in these nanoferrites. Rich magneto-optical properties of quinary Co0.4+xZn0.5-xLi0.1Fe2O4 (x = 0.0, 0.05 and 0.1) nanoferrites can find applications in the design and fabrication of magneto-optic and permanent magnet based devices.

Rock Magnetic Characterization of Fine Particles from Car Engines, Brake Pads and Tobacco: An Environmental Pilot Study on Oahu, Hawaii, USA

Today, it is well known that small airborne particles are very harmful to human health. For the first time in Hawaii we have conducted an environmental pilot study of fine magnetic particles on the island of Oahu, Hawaii, of particulate matter (PM) PM = 60, PM = 10, and PM = 2.5. In order to do a rock magnetic characterization we have performed low field susceptibility vs. temperature [k-T] experiments to determine the Curie points of small particles collected from exhaust pipes, as well as from brake pads of four different types of car engines using gasoline octane ratings of 87, 89, and 92. The Curie point determinations are very well defined and range from 292&#176C through 393&#176C and up to 660&#176C. In addition, we have conducted magnetic granulometry experiments on raw tobacco, burnt tobacco ashes, as well as on automotive engine exhaust, and brake pads in question. The results of the experiments show ferro and ferrimagnetic hysteresis loops with magnetic grain sizes ranging from superparamagnetic-multidomain [SP-MD], multidomain [MD] and pseudo-single domain [PSD] shown on the modified Day et al., diagram of Dunlop (2002). Thus far, the results we have obtained from this pilot study are in agreement with other studies conducted from cigarette ashes from Bulgaria. Our results could be correlated to the traffic-related PM in Rome, Italy where the SP fraction mainly occurs as coating of MD particles originated by localized stress in the oxidized outer shell surrounding the un-oxidized core of magnetite-like grains. All these magnetic particles have been reported to be very harmful to our human bodies (i.e. brain, lungs, heart, liver etc.).

In situ observation of electric-field induced magnetic domain evolution in (Ba,Ca)(Ti,Zr)O3–CoFe2O4 multiferroic films

The integration of ferroelectric and ferromagnetic promises an essential strategy of obtaining high performance electronic devices. In this work, we demonstrate in situ observation of electric field induced magnetic domain structure evolution for 0.5Ba(Ti0.8Zr0.2)O3–0.5(Ba0.7Ca0.3)TiO3–CoFe2O4 (BZT–0.5BCT/CFO) films, which manifests the magnetoelectric (ME) coupling between ferroelectric BZT–0.5BCT and ferrimagnetic CFO. The multiferroic behaviors of BZT–0.5BCT/CFO bilayers thin films were characterized by measuring ferroelectric domains, ferroelectric and ferrimagnetic hysteresis loops. The magnetic domain structure were investigated as functions of electric field, when the sample is applied with a voltage of 3 V, approximately 49.2% of the magnetization domain was varied in CFO thin films. The modulation of the domain structure could be attributed to the strain-induced mechanical transduction between the ferroelectric and magnetic films and modulation of the electron density of the CFO films. Direct observation of electric field induced magnetic domain evolution is significant since it gives a direct evidence of magnetoelectric coupling effect.

Magnetic and dielectric response of Sr0.95Nd0.05Fe12-xAlxO19 (x = 0.36, 0.60, 0.84 and 1.08) obtained by hydrothermal synthesis

Agglomerated single-phase Sr0.95Nd0.05Fe12-xAlxO19 nanocrystallites with 0.36 ≤ x ≤ 1.08 were synthesized hydrothermally and their properties were studied. Ferrimagnetic hysteresis loops were observed in the range 10-300K and the analysis of doping-induced changes in magnetization shows that Al3+ ions substitute the ferric ions in 4f2, 12k and 2a Wyckoff sites. The substitution in 4f2 and 12k sites induces electric dipoles in trigonal bipyramids and results in two relaxation processes apparent in the dielectric and electric response. Zero field cooling/field heating experiments in H = 100Oe have pointed to a coexistence of noncollinear and uniaxial magnetic moments in doped nanocrystalline hexaferrites and yield the (T1-x) phase diagram.

Sago starch: chelating agent in Sol-gel synthesis of cobalt ferrite nanoparticles

Starch from the stem of sago palm (Metroxylon sagu) was demonstrated as a chelating agent in the sol-gel synthesis of cobalt ferrite (CoFe2O4) nanoparticles. Variations in the weight ratio of metal nitrates to sago starch from 1:8 to 1:12 led to the particle size of 30–500 nm. However, further increase in sago starch to 1:16 resulted in ferrimagnetic hysteresis loops with a reduced coercive field and magnetization due to the second phase of hematite (α-Fe2O3). The synthesis conditions and products were comparable to those of the polyvinyl alcohol (PVA) sol-gel synthesis. Thus, sago starch can be implemented in the green synthesis of nanosized ferrites whose magnetic properties are tuned by varying of sol-gel compositions for each application.

Strain induced exchange-spring magnetic behavior in amorphous (TbDy)Fe2 thin films

In this paper, we report a strain induced exchange-spring magnetic behavior in sputter deposited (TbDy)Fe2 amorphous thin films with phase-separated layers of (TbDy)-rich and Fe-rich at room temperature. The magnetic hysteresis loops at different strain levels were obtained with a magneto-optic Kerr effect set-up incorporating a mechanical four-point bending fixture. The unstrained film exhibits a typical ferrimagnetic hysteresis loop while the strained structure exhibits step-like hysteresis loops representative of an exchange-spring magnetic system. The mechanically strained film changes the coercivity/remanence values from positive to negative. The observed magnetic changes under strain are attributed to magnetic anisotropy modifications in the highly magnetoelastic TbDy-rich layer.

A facile synthesis for magnetic ferberite nanostructured material

Iron-tungsten oxide nanospinel have been prepared by two methods: microwave combustion method and Pechini method. The W-Fe bimetallic ferberite was successfully synthesized by microwave-assisted techniques. The resultant magnetic nanocomposites were characterized by thermal analysis, X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, energy-dispersive X-ray, transmission electron microscopy, nitrogen adsorption, and magnetic properties measurement system. The prepared ferberite nanoparticles (50–65 nm) using microwave combustion method were pure monoclinic ferberite. The ferberite nanoparticles showed ferrimagnetic hysteresis loop with values of saturation magnetization and coercivity of 4.829 A.m2/Kg and 0.0312 T, successively.

Synchrotron X-ray absorption spectroscopy and magnetic characteristics studies of metal ferrites (metal = Ni, Mn, Cu) synthesized by sol-gel auto-combustion method

In this work, the metal ferrites MFe2O4 (M = Ni, Mn, Cu) were synthesized from metal nitrate precursors by the sol–gel auto-combustion method using diethanolamine (DEA) as a potential fuel. The crystal structures of these ferrite powders were characterized by X-ray diffraction (XRD) technique confirming the complete formation of the single-phase cubic spinel crystal structure. The ferrimagnetism characteristic and the difference of the magnetic properties such as saturation magnetization (Ms), remanent magnetization (Mr), and coercivity (Hc) for each after-calcined ferrite sample were scrutinized through the ferrimagnetic hysteresis loop (M–H) obtained from the vibrating sample magnetometer (VSM) measurement. Moreover, the cation distribution and valence state of these ferrites were investigated by the Ni, Mn, Cu, and Fe K-edge X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectra using the synchrotron radiation light source. From the XAS results, the analyses of both XANES and EXAFS spectra show the existence of accurate oxidation state for transition metal ions and the interionic distance to the nearest neighbors in the spinel crystal structure. In particular, the curve-fitting analysis of Ni, Mn, Cu, and Fe K-edge EXAFS spectra indicates that the degree of inversion in these metal ferrites is entirely different and found to be 0.2 for MnFe2O4, 0.8 for CuFe2O4, and 1.0 for NiFe2O4, which are the important information for understanding their effects on relevant magnetic properties.

Effect of CoFe2O4 mole percentage on multiferroic and magnetoelectric properties of Na0.5Bi0.5TiO3/CoFe2O4 particulate composites

Na0.5Bi0.5TiO3 (NBT), CoFe2O4 (CFO) as well as particulate composites containing different mole percentages of NBT and CFO were synthesized by the solid-state sintering route and characterized for their ferroelectric and ferrimagnetic hysteresis loops, magnetostriction and magnetoelectric (ME) output. The mole% of CFO was found to influence the ferroelectric and ferrimagnetic hysteresis loops as well as magnetostriction and piezomagnetic coefficients which in turn had a significant effect on the magnetoelectric voltage coefficient. The highest magnetoelectric voltage coefficient (α) of 0.5mV/cm/Oe was recorded in (65) NBT–(35) CFO composite.

Fabrication of ferrimagnetic FeOx thin film and the resistance switching of Au/FeOx/Pt heterostructure

By controlling the temperature and oxygen partial pressure, well polycrystalline Fe3O4 thin film on Pt substrate was fabricated, using a stoichiometric α-Fe2O3 target. A ferrimagnetic hysteresis loop and a Verwey transition at about 130 K were shown in the results of magnetic measurement. A sharp hysteretic resistance switching below Verwey transition temperature (Tv) was observed in I-V tests of the Au/Fe3O4/Pt heterostructure. Enlarged hysteresis by larger pulse delay and suppressed metal-insulator transition by larger source currents indicated that enhanced local Joule heating effect played an important role in the hysteresis of resistance switching.

Magnetoelectric and dielectric relaxation properties of the high Curie temperature composite Sr1.9Ca0.1NaNb5O15–CoFe2O4

A magnetoelectric (ME) composite ceramic 0.6Sr1.9Ca0.1NaNb5O15–0.4CoFe2O4 (SCNN–CFO) was prepared by a conventional solid state reaction method. Remarkable dielectric constant dispersion with a Curie temperature of 270 °C was observed. This relaxor composite exhibits ferroelectric as well as ferrimagnetic hysteresis loops at room temperature. A significant ME coupling effect was observed. On the basis of our studies, it is demonstrated that the lead-free high Curie temperature SCNN–CFO relaxor composite material can be used in the future development of ME devices.

Anisotropic magnetic properties ofCa3Co4O9:Evidence for a spin-density-wave transition at 27 K

The dc susceptibility $\ensuremath{\chi}$ of single crystal platelets of ${\mathrm{Ca}}_{3}{\mathrm{Co}}_{4}{\mathrm{O}}_{9}$ was measured in applied magnetic fields H below 55 kOe. At temperatures below 400 K, the crystals exhibited three magnetic transitions successively at ${T}_{\mathrm{SS}}\ensuremath{\sim}380\mathrm{K},$ ${T}_{\mathrm{SDW}}=27\mathrm{K},$ and ${T}_{\mathrm{ferri}}=19\mathrm{K}.$ The highest spin state (SS) transition was found to be discontinuous with the appearance of a thermal hysteresis loop about 20 K wide. At 27 K, a small shoulder in the $\ensuremath{\chi}(T)$ curve was observed only for $H\ensuremath{\perp}ab,$ indicating the formation of an incommensurate spin-density-wave (SDW) state, which was also confirmed by independent muon spin rotation and relaxation experiments. The lowest of ${T}_{\mathrm{ferri}}$ is a transition to a ferrimagnetic state, for which also a ferrimagnetic hysteresis loop was observed for $H\ensuremath{\perp}ab,$ but not for $H\ensuremath{\Vert}\mathrm{ab}.$ This anisotropic behavior indicated that the ferrimagnetic interaction is parallel to the c axis. Considering the alternating stacking structure of ${\mathrm{Ca}}_{3}{\mathrm{Co}}_{4}{\mathrm{O}}_{9}$ along the c axis, the ferrimagnetism is most likely caused by interlayer coupling between the $[{\mathrm{Ca}}_{2}{\mathrm{CoO}}_{3}]$ and $[{\mathrm{CoO}}_{2}]$ subsystems.