Temperature-dependent Magnetic Hysteresis Research Articles

An exotic uniaxial hexagonal ferrite with narrow self-biased ferrimagnetic resonance linewidths: Cu 18H hexaferrite

Traditional circulators utilize ferrites with low magnetocrystalline anisotropy driven by external magnetic bias fields. Hexagonal ferrites with a strong uniaxial anisotropy enable self-biased circulators, significantly reducing their volume, weight, and cost. Here, a unique uniaxial hexaferrite, Cu 18H hexaferrite, with narrow ferrimagnetic resonance (FMR) linewidth at zero magnetic bias field is reported. The temperature-dependent magnetic hysteresis loops show a significant decrease in coercivity from cryogenic to room temperature, indicating a transition from the hard to soft magnetic state. The crystallographic texture ensures a squareness ratio greater than 0.65 and leads to a strong internal bias field induced by the aligned easy-magnetization axes. Owing to the highly dense and oriented crystallites, the zero-field FMR exhibits excellent linewidths of ∼270–320 Oe, which are lower than those of most hexaferrites reported at the Ka-band. These results reveal the great potential of Cu 18H hexaferrite as a low-loss microwave ferrite used for self-biased circulators.

Correlation of hysteresis loop and domain structure of CoFeB/Pd multilayer at various temperatures

Temperature-dependent magnetic hysteresis loop, magnetic relaxation, and magnetic domain behavior of (4 Å CoFeB/10 Å Pd)4 multilayer were investigated by means of magneto-optical Kerr microscopy, where the hysteresis, relaxation, and domain structures are simultaneously observed on the same area from room temperature up to 450 K near the Curie temperature of the multilayer. Below 380 K, the hysteresis loops are found to have squareness about 1, while the loops become more slanted and eventually paramagnetic at temperatures higher than 430 K. Correspondingly, the magnetic domain patterns exhibit transitional behavior from a circular to dendritic structure with change of relative ratio between the reversed and non-reversed sub-domain areas with respect to the temperature.

Magneto-transport properties of Co3O4 nanoparticles added (Cu0.5Tl0.5)Ba2Ca2Cu3O10-δ superconducting phase

Solid-state reaction method was used to synthesize Cu0.5Tl0.5Ba2Ca2Cu3O10-δ (CuTl-1223) superconducting phase and sol-gel method was used to prepare cobalt oxide (Co3O4) magnetic nanoparticles. These Co3O4 nanoparticles were added in CuTl-1223 superconducting matrix to get (Co3O4)x/CuTl-1223; x = 0–2.00 wt.% nanoparticles-superconductor composites. The effects of Co3O4 nanoparticles on crystal structure, phase formation, phase purity and infield superconducting transport properties of CuTl-1223 phase were investigated at different operating temperatures and external applied magnetic fields. The crystal structure and phase formation of Co3O4 nanoparticles and CuTl-1223 superconductor were determined by X-ray diffraction (XRD) technique. XRD peaks of Co3O4 nanoparticles were well indexed according to FCC crystal structure and the average particle size of 70 nm was calculated by using Debye-Scherer's formula. The unaltered crystal structure of host CuTl-1223 superconducting phase (i.e. Tetragonal) with the addition of Co3O4 nanoparticles indicated the dispersion of nanoparticles at inter-granular sites. Temperature dependent magneto-transport superconducting properties of (Co3O4)x/CuTl-1223 composites were investigated by zero field cooled (ZFC) and field cooled (FC) magnetic moment versus temperature (M-T) measurements. The onset transition temperatures {TcOnset (K)} was decreased along with the suppression of diamagnetic amplitude of CuTl-1223 superconducting phase with the addition of magnetic Co3O4 nanoparticles. Temperature dependent magnetic hysteresis (M-H loops) measurements of (Co3O4)x/CuTl-1223 composites were carried out at different operating temperatures from 5 K to 150 K. Critical current density (Jc) was calculated from M-H loops measurements by using Bean's model. Like the suppression of TcOnset (K) values, Jc was also decreased with the inclusion of Co3O4 nanoparticles. It was also observed that variation of Jc with H followed the power law Jc = βH−α at low operating temperatures 5 K and 20 K only.

A Temperature-Dependent Hysteresis Model for Soft Ferrites

This paper introduces a temperature-dependent hysteresis model based on a vectorial elemental operator with temperature-sensitive spontaneous magnetization and biaxial anisotropy for the soft ferrites. Detailed analysis of the temperature-dependent magnetic properties of one elemental operator has been presented thereafter. With the help of the proposed vector elemental operator and the 2-D Gaussian distribution function, the temperature-dependent magnetic hysteresis of soft ferrites can be simulated. This model is validated by the substantial agreement between the simulated and measured major hysteresis loops of a soft ferrite sample Siemens 4C65 at different temperatures with slight acceptable error.

Temperature dependent magnetic coupling between ferromagnetic FeTaC layers in multilayer thin films

We report systematic investigations on temperature dependent magnetic coupling between ferromagnetic FeTaC layers and resulting magnetic properties of multilayer structured [FeTaC (~67nm)/Ta(x nm)]2/FeTaC(~67nm)] thin films, which are fabricated directly on thermally oxidized Si substrate. As-deposited amorphous films are post annealed at different annealing temperatures (TA=200, 300 and 400°C). Structural analyzes reveal that the films annealed at TA≤200°C exhibit amorphous nature, while the films annealed above 200°C show nucleation of nanocrystals at TA=300°C and well-defined α-Fe nanocrystals with size of about 9nm in amorphous matrix for 400°C annealed films. Room temperature and temperature dependent magnetic hysteresis (M–H) loops reveal that magnetization reversal behaviors and magnetic properties are strongly depending on spacer layer thickness (x), TA and temperature. A large reduction in coercivity (HC) was observed for the films annealed at 200°C and correlated to relaxation of stress quenched in during the film deposition. On the other hand, the films annealed at 300°C exhibit unusual variation of HC(T), i.e., a broad minimum in HC(T) vs T curve. This is caused by change in magnetic coupling between ferromagnetic layers having different microstructure. In addition, the broad minimum in the HC(T) curve shifts from 150K for x=1 film to 80K for x=4 film. High-temperature thermomagnetization data show a strong (significant) variation of Curie temperature (TC) with TA (x). The multilayer films annealed at 200°C exhibit low value of TC with a minimum of 350K for x=4 film. But, the films annealed at 400°C show largest TC with a maximum of 869K for x=1 film. The observed results are discussed on the basis of variations in magnetic couplings between FeTaC layers, which are majorly driven by temperature, spacer layer thickness, annealing temperature and nature of interfaces.

Universal Hysteresis Behavior of Double Perovskite Ba<sub>2-</sub><sub>x</sub>La<sub>x</sub>FeMoO<sub>6</sub>

We have investigated temperature-dependent magnetic hysteresis loop behavior of Ba2-xLaxFeMoO6 with double perovskite structure by means of a vibrating sample magnetometer (VSM). As partial substitution of Ba2+ by La3+ is varied from x = 0.1 to 0.3, TC is found to increase from 324 to 345 K. Interestingly, however, hysteresis loop area, remanent magnetization, and coercivity are found to follow a universal behavior with respect to a temperature variation regardless of the Ba2+ substitution.

Magnetoelectric properties of PbZr0.53Ti0.47O3–Ni0.65Zn0.35Fe2O4 multiferroic nanocomposites

A different kind of multiferroics with ferroelectric–ferrimagnetic (FE–FM) composites: (1 − x) PbZr0.53Ti0.47O3–x Ni0.65Zn0.35Fe2O4 with x = 0.10, 0.20 and 0.30, were synthesized by a powder-in-sol precursor hybrid processing route. Structural analysis with X-ray diffraction (XRD) data revealed the presence of both PbZr0.53Ti0.47O3 (PZT) and Ni0.65Zn0.35Fe2O4 (NZFO) pure phases in the PZT–NZFO composites. Scanning electron micrographs (SEM) clearly disclose distribution of both PZT and NZFO phases throughout the sample. Dielectric and electrical properties of the system have been investigated in a wide range of frequency at different temperatures. Dielectric constant (er) as a function of temperature reveals the paraelectric–FE transition temperature at ~408 °C having maximum value of er at the peak [e r max = 1,200] with another low temperature anomaly at ~297 °C, very close to the magnetic Curie temperature of the NZFO ferrite (Tc = 300 °C) for the x = 0.1 FE–FM composite. The impedance spectroscopy data of these composites show clearly, contribution of both grain and grain boundary effect in the electrical properties of the composites. Negative temperature coefficient of resistance (NTCR) behavior of the materials indicates their semi-conducting nature. The ac conductivity spectrum is found to obey Johnscher’s power law very well. The temperature-dependent magnetization hysteresis (M–H) loops of the PZT/NZFO composite show excellent non-saturating ferrimagnetic behavior with increase in both coercive field (Hc) and remanent magnetization (Mr) when the NZFO content in the composite is increased. Polarization (P) versus electric field (E) studies at 300 K give conclusive evidence of the presence of spontaneous polarization in all the three composites (x = 0.1, 0.2 and 0.3). However, area of P–E loop, coercive field (Ec) and remanent polarization (Pr) are found to decrease noticeably with the increase of the NZFO content (x) in these composites.

Superparamagnetic and ferromagnetic Ni nanorod arrays fabricated on Si substrates usingelectroless deposition

The microstructures and magnetic properties of nickel nanorods fabricated using an anodicalumina oxide template and electroless deposition were investigated. The as-depositednanorods were found to contain nanocrystalline grains with an average size of∼2–3 nm. The temperature-dependent magnetic hysteresis curves indicated superparamagneticbehavior of the as-deposited rods as a result of the reduction of ferromagnetic crystallites. Thesuperparamagnetic (SM) Ni nanorods transformed into ferromagnetic (FM) ones when annealed at400 °C. Results from dark-field transmission electron microscopy reveal that the microstructure ofthe rods tends to form a laminar structure with grain growth parallel to the long axis of therods, together with the enhancement of ferromagnetic ordering along the same direction.The results suggest that the SM–FM phase transition obtained is microstructure driven.The Ni nanorods manufactured by the electroless deposition also have the potential toserve as magnetic building blocks in nanoscale devices, such as high-frequency inductors.On-chip magnetic spiral inductors were fabricated using these nanorods, andit was demonstrated that the nanorods can enhance inductance up to 6 GHz.