Temperature-dependent Hysteresis Research Articles

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.

Thermally activated trap charges responsible for hysteresis in multilayer MoS2 field-effect transistors

Hysteresis, which is induced by both extrinsic and intrinsic causes, is often observed in molybdenum disulphide (MoS2) field-effect transistors (FETs), and several extrinsic hysteresis effects have been reported in unpassivated bottom-gate MoS2 device structures. In this study, interface-trap-induced hysteresis and other electrical properties are examined. We experimentally investigate thermally activated trap charges near a silicon-dioxide (SiO2)-MoS2 interface that gives rise to hysteresis in a multilayer MoS2 FET in a temperature region of 10–300 K. The threshold voltage (VTH) and field-effect mobility (μFE) decrease with the increase in temperature, regardless of the gate-bias sweep direction. The hysteresis that coincides with the trend of subthreshold swing increases sharply above T = 150 K as the released charges from interface traps become dominant over the fixed charges. Based on a temperature-dependent hysteresis analysis, we discussed the activation energy of interface traps and maximum interface trap density of the fabricated multilayer MoS2 FET.

Fabrication of flexible oriented magnetic thin films with large in-plane uniaxial anisotropy by roll-to-roll nanoimprint lithography

Here, we report wafer scale fabrication of densely packed Fe nanostripe-based magnetic thin films on a flexible substrate and their magnetic anisotropy properties. We find that Fe nanostripes exhibit large in-plane uniaxial anisotropy and nearly square hysteresis loops with energy products (BHmax) exceeding 3MGOe at room temperature. High density Fe nanostripes were fabricated on 70nm flexible polyethylene terephthalate (PET) gratings, which were made by a roll-to-roll (R2R) UV nanoimprint lithography technique. We observed large in-plane uniaxial anisotropies along the long dimension of nanostripes that can be attributed to the shape. Temperature dependent hysteresis measurements confirm that the magnetization reversal is driven by non-coherent rotation reversal processes.

Phase evolution and correlation between tolerance factor and electromechanical properties in BNT-based ternary perovskite compounds with calculated end-member Bi(Me0.5Ti0.5)O3 (Me = Zn, Mg, Ni, Co).

In this work, the structure of end-member Bi(Me0.5Ti0.5)O3 (Me = Zn, Ni, Mg, Co) was calculated through a first-principles method and lead-free piezoelectric ternary systems (0.94 -x)(Bi0.5Na0.5)TiO3-0.06BaTiO3-xBi(Me0.5Ti0.5)O3 (Me = Zn, Ni, Mg, Co) (BNT-BT-Bi(Me0.5Ti0.5)O3) were designed to achieve a large strain response for actuator applications. Composition-driven phase transition characteristics and the resulting associated piezoelectric and electromechanical properties were systematically investigated, and schematic phase diagrams were constructed. XRD measurements, Raman spectra analysis and temperature-dependent polarization and strain hysteresis loops indicate that Bi(Me0.5Ti0.5)O3 substitution induces a phase transformation from a ferroelectric rhombohedral to an ergodic relaxor pseudo-cubic phase, accounting for the large strain response (>0.3%) with a high normalized strain Smax/Emax (≥550 pm V(-1)) at around the corresponding critical composition in the vicinity of room temperature. In addition, correlations between the tolerance factor t of the added end-member, the calculated tetragonality and the morphotropic phase boundary (MPB) composition were sought. In comparison to other reported BNT-based systems, there is a noticeable correlation between the MPB composition and the calculated tetragonality of the end-member Bi(Me0.5Ti0.5)O3, and the t value corresponding to the formation of the MPB composition is approximately 0.981 in the present ternary system with low tolerance factor end-members. As a result, we believe that the general correlations and design principles obtained from the present comprehensive research will be effective to predict the approximate MPB region quickly in BNT-based ceramics with an excellent actuating performance.

Synthesis and characterizations of BNT–BT–KNN ceramics for energy storage applications

Dielectric, ferroelectric and piezoelectric properties of the (0.94–x) Bi0.5Na0.5TiO3–0.06BaTiO3–xK0.5Na0.5NbO3/BNT–BT–KNN ceramics with x = 0.02 and 0.05 (2KNN and 5KNN) were studied in detail. Dielectric study and temperature-dependent polarization hysteresis loops indicated a ferroelectric-to-antiferroelectric transition at depolarization temperature (Td). The low Td in both the ceramic samples suggested the dominant antiferroelectric ordering at room temperature (RT), which was also confirmed by RT polarization and strain hysteresis loops studies. Antiferroelectric-to-paraelectric phase transition temperature (Tm) was nearly same for both systems. The 5KNN ceramic samples showed the relaxor behaviour. The values of the dielectric constant, Td, and maximum strain percentage increased, whereas the coercive field and remnant polarization decreased with the increase of the KNN percentage in the BNT–BT–KNN system. High-energy storage density ∼0.5 J/cm3 at RT hinted about the suitability of the 5KNN system for energy storage applications.

Unravelling the Proton Conduction Mechanism from Room Temperature to 553 K in a 3D Inorganic Coordination Framework.

The preparation of proton-conducting materials that are functional and stable at intermediate temperatures (393-573 K) is a focal point of fuel cell development. The purely inorganic material, HNd(IO3)4, which possesses a dense 3D framework structure, can reach a maximum of 4.6 × 10(-4) S·cm(-1) at 353 K and 95% relative humidity and exhibit a high conductivity of 8.0 × 10(-5) S·cm(-1) from 373 to 553 K under the flow of wet N2. HNd(IO3)4 exhibits a variety of improvements including high thermal stability, low solubility in water, and resistance to reducing atmosphere. The proton conductivity in such a wide temperature range originates from the intrinsic liberated protons in the structure and the resulting 1D hydrogen-bonding network confirmed by bond valence sum calculation and solid-state NMR analysis. Moreover, two different activation energies are observed in different temperature regions (0.23 eV below 373 K and 0.026 eV from 373 to 553 K), indicating that two types of proton motion are responsible for proton diffusion, as further domenstrated by temperature-dependent open-circuit voltage hysteresis in a tested fuel cell assembly as well as variable-temperature and double quantum filtered solid-state NMR measurements.

Electric field and temperature scaling of polarization reversal in silicon doped hafnium oxide ferroelectric thin films

HfO2-based binary lead-free ferroelectrics show promising properties for non-volatile memory applications, providing that their polarization reversal behavior is fully understood. In this work, temperature-dependent polarization hysteresis measured over a wide applied field range has been investigated for Si-doped HfO2 ferroelectric thin films. Our study indicates that in the low and medium electric field regimes (E<twofold coercive field, 2Ec), the reversal process is dominated by the thermal activation on domain wall motion and domain nucleation; while in the high-field regime (E>2Ec), a non-equilibrium nucleation-limited-switching mechanism dominates the reversal process. The optimum field for ferroelectric random access memory (FeRAM) applications was determined to be around 2.0MV/cm, which translates into a 2.0V potential applied across the 10nm thick films.

Universal Hysteresis Behavior of Double Perovskite Ba&lt;sub&gt;2-&lt;/sub&gt;&lt;sub&gt;x&lt;/sub&gt;La&lt;sub&gt;x&lt;/sub&gt;FeMoO&lt;sub&gt;6&lt;/sub&gt;

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.

Thermally activated coercivity in core-shell permanent magnets

Finite element micromagnetic simulations are used to compute the temperature-dependent hysteresis properties of Nd2Fe14B permanent magnets in order to assess the influence of a hard (Dy,Nd)2Fe14B shell. The simulations show that the 4 nm thick shell cancels out the reduction in coercivity from an outer defect layer, which is known to exist at the grain boundaries in NdFeB permanent magnets. Activation volumes are computed and shown to depend on the structure's configuration as well as the temperature.

Temperature dependence scaling behavior of the dynamic hysteresis in 0.715Bi0.5Na0.5TiO3-0.065BaTiO3-0.22SrTiO3 ferroelectric ceramics

Temperature dependent dynamic hysteresis of 0.715Bi0.5Na0.5TiO3-0.065BaTiO3-0.22SrTiO3 (BNT-BT-ST) bulk ferroelectric ceramic was systematically studied. The scaling relations were estimated for corrective electric field remnant polarization and hysteresis loop area as a function of temperature It was observed that and for a constant magnitude of electric field To understand the domain dynamics, back-switching polarization as a function of is also predicted. The relation between back-switching polarization and temperature is estimated by well described Arrhenius law to evaluate the average activation energy. It also depends on the applied electric field; the relation fits well to a simple exponential decay function. The saturation polarization as a function of was also evaluated to estimate the electrocaloric effect. It was found that electrocaloric effect and heat extract capacity in BNT-BT-ST ceramic is of a similar order to that observed in most other lead-free bulk ferroelectric ceramics. It can be said that BNT-BT-ST is also a promising material for solid state refrigeration. These results can be helpful to understand the temperature dependent hysteresis behavior and polarization switching in lead-free ferroelectric ceramics.

Magnetism and electrical transport properties of La1−x−y Pr y Ca x MnO3 (x ≈ 0.42, y ≈ 0.40) thin films: role of microstructural disorder

We report the effect of substrate-induced lattice disorder on the balance between the coexisting antiferromagnetic/charge-ordered insulating (AFM/COI) and ferromagnetic metallic (FMM) phases and the dynamics of the phase transition in the strongly phase-separated single-crystalline La1−x−yPryCaxMnO3 (x ≈ 0.42, y ≈ 0.40) thin films. At lower degree of disorder, the delicate balance between AFM/COI and FMM phases gives rise to a magnetically disordered/non-equilibrium magnetic liquid, which shows a strong supercooling behaviour and colossal thermal hysteresis in temperature dependence of magnetization (M–T) and resistivity (ρ–T). At lower temperatures, the disordered liquid freezes to yield a randomly frozen glassy state. The enhanced lattice disorder quenches the non-FM phases and promotes AFM/COI–FMM phase transition, which in turn reduces the magnetic frustration and lowers the degree of supercooling. The enhanced FMM fraction also unblocks the blocked magnetic states and results in the vanishing of the pronounced minimum in the ρ–T curve observed well above the glass transition. Our results show that the impact of enhanced lattice disorder is in many ways similar to that of the extrinsic magneto-thermodynamic perturbations.

Heterospin single-molecule magnet behaviors after irradiation of polymorphous 2:2 cyclic diazo-cobalt(II) complexes

Three kinds of crystals (crystals, α, β, and γ) of 2:2 cyclic cobalt complexes formulating as [Co(Br-hfpip)2(D2py2)]2 X: X=2CH2Cl2 (1dα), 4CH2Cl2 (1dβ), and 4CH2Cl2·4EtOH (1dγ) and Br-hfpip=1,1,1,5,5,5-hexafluoro-4-(4-bromophenylimino)-2-pentanonate, were obtained and were determined to be polymorphous by X-ray crystallography, having the space groups of P1¯ for 1dα and 1dβ, and P21/n for 1dγ. In three polymorphs, the local coordination structures of cobalt complex units in the molecule were the same; compressed octahedral. The molecular structure for 1dα was different from those for 1dβ and 1dγ. The dihedral angles between the X–Y plane and the pyridine ring were 43° and 44° for 1dα and 70–80° for 1dβ and 1dγ. In the crystal packings, 1dα had a short contact between the bromo substituent in hfpip ligand and the carbon at the β position of the pyridine ring in D2py2, while 1dβ and 1dγ had no short contact between the magnetically significant atoms. The powder X-ray diffraction (PXRD) patterns for the crushed samples of three polymorphs indicated that the crystal structures were changed by loosing crystal solvent and 1dα and 1dβ were microcrystals (1dα′ and 1dβ′), while 1dγ became amorphous (1dγ′). In dc and ac magnetic measurements after irradiation of crushed samples (1dα′, 1dβ′, and 1dγ′), the photoproducts, 1cα′, 1cβ′, and 1cγ′ exhibited slow magnetic relaxation and magnetic hysteresis. 1cα′ showed a single-molecule magnet (SMM) behavior with the effective activation barrier, Ueff/kB=98K and coercive force, Hc=2.9kOe at 1.9K affected by the intermolecular antiferromagnetic interaction. 1cβ′ showed the magnetic behavior with Ueff/kB=134K and Hc=13kOe at 1.9K typical of heterospin SMM. In 1cγ′, weak χmol″ signals with frequency dependency and the temperature dependent hysteresis loop; Hc=1.1kOe at 1.9K, were observed.

Temperature Dependent Electrical Resistance of Proton Irradiated and Non-irradiated C60 Micro-rods

Self-assembled fullerene C60 micro-rods on borosilicate substrates were synthesized via liquid-liquid interfacial precipitate method (LLIP) and subsequently irradiated with 2 MeV H+ with fluencies ranging from 5.0 × 1013 - 9.0 ×1015 H+cm-2. The resistance measurements were conducted under light illumination of white, red, yellow and blue colors and the results were compared to zero illumination. After H+ irradiation, the fullerene C60 micro-rods became chemically inert due to weakened C–C bonds within C60 molecules that generated polymeric yields that are insoluble in toluene. Alteration in optical band-gap triggering color transformation from black to yellowish was observed, signifying the existence of loosely bound pi-electrons being excited by visible light. Resistivity measurements revealed wavelength and temperature dependent hysteresis with first order transition behavior at 337K. These behaviors qualify fullerene C60 micro-rods for optoelectronic switches and optical sensors applications.

Temperature-dependent hysteresis effects in perovskite-based solar cells

Time- and temperature-dependent photocurrent transient analysis suggests that hysteresis effects are associated with multiple charging–discharging processes in perovskite solar cells.

Structural transition and temperature-driven conductivity switching of single crystalline VO2(A) nanowires

Single crystalline VO2(A) nanowires were synthesized by a facile hydrothermal method. The structural transition and temperature-driven conductivity switching of the VO2(A) nanowires were investigated. Our experimental results show that VO2(A) nanowires exhibit a distinct structural transition accompanied with an order of magnitude change in resistance, and a clear temperature-dependent current switching hysteresis. In order to analyze experimental results, theoretically, the electrical conductivity behavior was found to be consistent with Mott's small polaron model, the first-principles calculations also indicated that the apical V–O bond changes were mainly responsible for the band gap evolution and hence led to the conductivity switching.

Origin of the large strain response in tenary SrTi0.8Zr0.2O3 modified Bi0.5Na0.5TiO3–Bi0.5K0.5TiO3 lead-free piezoceramics

The perovskite oxides (1 − x)Bi0.5(Na0.9K0.1)0.5TiO3–xSrTi0.8Zr0.2O3 (SZT1000x, x = 0, 0.2, 0.4, 0.6, 0.8, and 1 %) were prepared via the conventional solid-state reaction method. The room temperature ferroelectric P–E loops coordinate with polarization current density J–E curves illustrated the changes of ferroelectric domains and polar nanoregions under different driving fields exhaustively. The composition and electric field dependent strain behavior of this system were investigated to develop a lead-free piezoelectric material with a large strain response at a lower electric field. A large strain of 0.44 % (S max/E max = 744 pm/V) at an applied field of 50 kV/cm was obtained at the composition of 0.6 mol% SZT. Temperature-dependent hysteresis measurements reveal the primary origin of the large strain is due to the presence of a nonpolar phase at a zero field. Upon the application of an electric field, the nonpolar phase that can easily transform into a long-range ferroelectric phase, and then brings the system back to its unpoled state once the applied electric field is removed. Notably, the electric field required to deliver large strains is reduced to 40 kV/cm while the S max/E max reached up to 717 pm/V, indicating that the developed material is highly promising for actuator applications.

Exchange interactions at the origin of slow relaxation of the magnetization in {TbCu₃} and {DyCu₃} single-molecule magnets.

New {TbCu3} and {DyCu3} single-molecule magnets (SMMs) containing a low-symmetry Ln(III) center (shape measurements relative to a trigonal dodecahedron and biaugmented trigonal prism are 2.2-2.3) surrounded by three Cu(II) metalloligands are reported. SMM behavior is confirmed by frequency-dependent out-of-phase ac susceptibility signals and single-crystal temperature and sweep rate dependent hysteresis loops. The ferromagnetic exchange interactions between the central Ln(III) ion and the three Cu(II) ions could be accurately measured by inelastic neutron scattering (INS) spectroscopy and modeled effectively. The excitations observed by INS correspond to flipping of Cu(II) spins and appear at energies similar to the thermodynamic barrier for relaxation of the magnetization, ~15-20 K, and are thus at the origin of the SMM behavior. The magnetic quantum number M(tot) of the cluster ground state of {DyCu3} is an integer, whereas it is a half-integer for {TbCu3}, which explains their vastly different quantum tunneling of the magnetization behavior despite similar energy barriers.

Bipolar electro-caloric effect in SrxBa(1−x)Nb2O6 lead-free ferroelectric single crystal

Here we report the anomalous electro-caloric effect (ECE) observed in lead-free SrxBa(1−x)Nb2O6 (, 0.61 and 0.75) ferroelectric single crystals. Temperature-dependent hysteresis measurement revealed that the spontaneous polarization of SrxBa(1−x)Nb2O6 single crystals with all the compositions under investigation decreases with a decrease in the temperature below the temperature of the dielectric maxima . As a consequence, these crystals exhibited negative electro-caloric effect at lower temperature along with the usual positive ECE above . The EC coefficient obtained near is 0.21, 0.43 and 0.28 K mm/kV for , 0.61 and 0.75 samples, respectively. The maximum values of in the negative ECE region are −1.4, −0.81 and for 50SBN, 61SBN and 75SBN, respectively.

Temperature-Dependent Hysteresis Behavior Modeling of the Open Circuit Potential and Impedance of LiFePO4 Batteries

Lithium Iron Phosphate (LFP) batteries present many challenges for accurate behavioral modeling during charge and discharge processes, as the two-phase interactions between cathode particles create multiple stable, degenerate distributions of lithium across the electrode. These degenerate distributions can cause the battery’s equilibrium open circuit potential (VOC) and equivalent series resistance (ESR) to vary at a given temperature and state of charge (SOC) depending on recent history, such as if the battery was most recently charged or discharged, a phenomenon known as hysteresis. A behavioral two-capacitor model was developed that incorporates temperature-dependent hysteresis between charge and discharge (affecting both VOC and ESR) and mimics temperature-dependent and SOC-dependent kinetics and impedance. The model includes a coupled finite volume thermal transport model with heat generation calculated due to a combination of Ohmic heating and entropic heating. The model was validated against high C-rate cyclic charge and discharge, as well as intermittent discharge and charge profiles at temperatures ranging from zero to 50°C. It is seen that for temperatures near 0°C, new physics come into play during recharge and that VOC hysteresis between charge and discharge increases as temperature decreases.

Magnetic Properties of 1:2 Mixed Cobalt(II) Salicylaldehyde Schiff-Base Complexes with Pyridine Ligands Carrying High-Spin Carbenes (Scar = 2/2, 4/2, 6/2, and 8/2) in Dilute Frozen Solutions: Role of Organic Spin in Heterospin Single-Molecule Magnets

The 1:2 mixtures of Co(p-tolsal)2, p-tolsal = N-p-tolylsalicylideniminato, and diazo-pyridine ligands, DXpy; X = 1, 2, 3l, 3b, and 4, in MTHF solutions were irradiated at cryogenic temperature to form the corresponding 1:2 cobalt-carbene complexes Co(p-tolsal)2(CXpy)2, with Stotal = 5/2, 9/2, 13/2, 13/2, and 17/2, respectively. The resulting Co(p-tolsal)2(CXpy)2, X = 1, 2, 3l, 3b, and 4, showed magnetic behaviors characteristic of heterospin single-molecule magnets with effective activation barriers, Ueff/kB, of 40, 65, 73, 72, and 74 K, for reorientation of the magnetic moment and temperature-dependent hysteresis loops with a coercive force, Hc, of ∼0, 6.2, 10, 6.5, and 9.0 kOe at 1.9 K, respectively. The relaxation times, τQ, due to a quantum tunneling of magnetization (QTM) were estimated to be 1.6 s for Co(p-tolsal)2(C1py)2, ∼2.0 × 10(3) s for Co(p-tolsal)2(C2py)2, and >10(5) s for Co(p-tolsal)2(CXpy)2; X = 3b, 3l, and 4. In heterospin complexes, organic spins, carbenes interacted with the cobalt ion to suppress the QTM pathway, and the τQ value increased with increasing the Stotal values.