Dc Magnetic Field Dependence Research Articles

Achieving superconductivity with higher Tc in lightweight Al–Ti–Mg alloys: Prediction using machine learning and synthesis via high-pressure torsion process

Aluminum (Al) and titanium (Ti) are superconducting materials but their superconducting transition temperatures (Tc) are quite low as 1.20 and 0.39 K, respectively, while magnesium (Mg) never exhibits superconductivity. In this study, we explored new superconductors with higher Tc in the Al–Mg–Ti ternary system, along with the prediction using machine learning. High-pressure torsion (HPT) is utilized to produce the superconducting states. While performing AC magnetization measurements, we found, for the first time, superconducting states with Tc=4.0 and 7.3 K for a composition of Al:Ti = 1:2. The magnetic anomalies appeared more sharply when the sample was processed by HPT at 573 K than at room temperature, and the anomalies exhibited DC magnetic field dependence characteristic of superconductivity. Magnetic anomalies also appeared at ∼55 and ∼93 K, being supported by the prediction using the machine learning for the Al–Ti–O system, and this suggests that Al–Ti oxides play an important role in the advent of such anomalies but that the addition of Mg could be less effective.

Magnetoelectric Coupling in Epitaxial Multiferroic BiFeO3–BaTiO3 Composite Thin Films

Herein, the magnetoelectric (ME) performance of epitaxial multilayer composite films built from nanometer‐thick layers of multiferroic BiFeO3 and ferroelectric BaTiO3 is reviewed. A successful implementation of shadow‐mask pulsed laser deposition considerably reduces the interface and surface roughness of the multilayers. In dependence of double‐layer thickness and the degree of structural perfection, the multilayers show high ME voltage coefficients up to 480 V cm−1 Oe−1 at 300 K and 0 T bias magnetic field. With decreasing double‐layer thickness, an interface‐driven effect critically enhances the ME coupling in this strain and charge–comediated system. Interestingly, the characteristics of temperature and DC magnetic field dependencies of magnetoelectric voltage coefficients change with the transition from the 2D to 3D character of the single layers, i.e., for BiFeO3 layers thicker than 5 nm within the multilayers. These changes are attributed to variations of the contributing ME coupling mechanisms. Furthermore, scanning transmission electron microscopy (STEM) with energy‐dispersive X‐ray (EDX) spectroscopy mapping‐based nanoanalysis indicates that chemical effects at the interfaces play an important role for the ME performance of the BiFeO3–BaTiO3 multilayer thin films.

Influence of individual phases on the magnetoelectric coupling and electromechanical response in (1 − x)Ba0.83Ca0.10Sr0.07TiO3-xBiFeO3 (x = 0–0.30) multiferroic composites

BaTiO3 based composites have been widely utilized to achieve better ferroelectric and magnetoelectric characteristics. BiFeO3 is one of materials that exhibit superior magnetoelectric characteristics in single phase. In this work, (1 − x)Ba0.83Ca0.10Sr0.07TiO3-xBiFeO3 (x = 0–0.30) multiferroic composites have been synthesized using mechano-chemical activation method. The strategy is to achieve optimum ferroelectric and ferromagnetic properties without hampering the inherent dielectric and ferroelectric characteristics of Ba0.83Ca0.10Sr0.07TiO3. The synthesized composites have shown diphasic nature with homogeneous grains and clearly distinguishable grain boundaries. The composition with x = 0.10 exhibits superior electrical properties, which are attributed to optimum resistivity and increased tetragonal lattice distortion introduced by BiFeO3 addition. The modification in bond length and bond angle leads to a significant enhancement in ferromagnetic characteristics of prepared composites. The composites have shown a gradual increase in magnetoelectric characteristics and substantial DC magnetic field dependence. This work provides an optimum composition and feasible route to prepare high-performance magnetoelectric composites.

Unusual magnetic behaviour of binary YbNi3 alloy

Measurements on the magnetic, electronic transport and thermal properties of the binary YbNi3 alloy are reported. The results are consistent with a magnetic transition at 3.9 K of Ferrimagnetic nature, as established from the AC magnetic susceptibility and the field dependence of DC magnetization and specific heat at low temperatures. Moreover, magnetic and electrical resistivity measurements reveal the presence of an additional magnetic transition around 50 K. The unusual magnetic ground state for Yb compounds is explained by the presence of different inequivalent Yb and Ni crystallographic sites, within an orthorhombic structure of the PuNi3-type (space group R3¯m), with similar temperature scales of the magnetic and Kondo interactions (TK=6K). The results are also compared to those reported for other binary Yb-Ni and RNi3 (R-Rare Earth) alloys.

Magnetic and electrical transport of the cation-deficient LaMnO3: Common origin for both Sr-doping and self-doping effects

We have investigated the effect of cation deficiency on the electric and magnetic properties of LaMnO3 in terms of both substitution of La by a divalent ion (Sr2+) and creating La-deficiency. The temperature and magnetic field dependence of electrical resistivity (ρ) and dc magnetization were studied. All the compounds are to be found in rhombohedral structure. The excess oxygen in all compounds was detected through iodometric titration. The metal to semiconducting transition and the paramagnetic to ferromagnetic transition is found to decrease with Mn4+ for all samples. The occurrence of magnetoresistance (MR) at low temperature and low field for La-deficient compounds is suggested due to the tunneling of electron through the grain boundary (GB). The nonlinear current-voltage (I–V) characteristic for La-deficient compounds indicates inelastic tunneling via localized states dominate the transport mechanism.

Evidence for reentrant spin glass behavior in transition metal substituted Co-Ga alloys near critical concentration

In the present study magnetic and electrical transport properties of transition metal substituted Co-Ga alloys (near critical cobalt concentration) have been investigated. Analysis of temperature and field dependence of dc magnetization and ac susceptibility (ACS) data suggests an evidence of reentrant spin glass (RSG) phase in Co55.5TM3Ga41.5 (TM = Co, Cr, Fe, Cu). The magnetic transition temperatures (TC and Tf) are found to depend on the nature of TM element substitution with the exchange coupling strength Co-Fe > Co-Co > Co-Cu > Co-Cr. From magnetization dynamics precise transition temperatures for the glassy phases are estimated. It is found that characteristic relaxation times are higher than that of spin glasses with minimal spin-cluster formation. The RSG behavior has been further supported by the temperature dependence of magnetotransport studies. From the magnetic field and substitution effects it has been established that the magnetic and electrical transport properties are correlated in this system.

Role of initial heat treatment of the ferrite component on magnetic properties in the composite of ferrimagnetic Co1.75Fe1.25O4 ferrite and non-magnetic BaTiO3 oxide

We have prepared a composite of ferrimagnetic ferrite Co1.75Fe1.25O4 and non-magnetic oxide BaTiO3. The ferrite composition Co1.75Fe1.25O4 has been prepared by chemical co-precipitation and subsequently heated at different temperatures. The heat treated ferrite powder has been mixed with BaTiO3 powder with mass ratio 1:1 and the mixed powder has been finally heated at 1000°C to form composite material. Structural phase of the composite material has been confirmed by high quality Synchrotron X-ray diffraction pattern and Micro-Raman spectra. The grain surface morphology and elemental composition have been studied by Scanning electron microscope and Energy dispersive X-ray analysis. The distribution of magnetic exchange interactions and blocking behavior of the ferrimagnetic grains in composite samples has been understood by analyzing the temperature and magnetic field dependence of dc magnetization. Finally, information on modified micro-structure and ferrimagnetic parameters in composite samples has been obtained as the variation of annealing temperature of the ferrite component before making composite.

Ba(Zn(1-2x)MnxCux)2As2: A Bulk Form Diluted Ferromagnetic Semiconductor with Mn and Cu Codoping at Zn Sites.

We report the synthesis and characterization of a bulk form diluted magnetic semiconductor Ba(Zn1−2xMnxCux)2As2 with the crystal structure identical to that of “122” family iron based superconductors and the antiferromagnet BaMn2As2. No ferromagnetic order occurs with (Zn, Mn) or (Zn, Cu) substitution in the parent compound BaZn2As2. Only when Zn is substituted by both Mn and Cu simultaneously, can the system undergo a ferromagnetic transition below TC ~ 70 K, followed by a magnetic glassy transition at Tf ~ 35 K. AC susceptibility measurements for Ba(Zn0.75Mn0.125Cu0.125)2As2 reveal that Tf strongly depends on the applied frequency with and a DC magnetic field dependence of , demonstrating that a spin glass transition takes place at Tf. As large as −53% negative magnetoresistance has been observed in Ba(Zn1−2xMnxCux)2As2, enabling its possible application in memory devices.

Reentrant spin glass ordering in an Fe-based bulk metallic glass

We report the results of the complex susceptibility, temperature, and field dependence of DC magnetization and the nonequilibrium dynamics of a bulk metallic glass Fe40Co8Cr15Mo14C15B6Er2. Solid indication of the coexistence of reentrant spin glass (SG) and ferromagnetic orderings is determined from both DC magnetization and AC susceptibility under different DC fields. Dynamics scaling of AC susceptibility indicates critical slowing down to a reentrant SG state with a static transition temperature Ts = ∼17.8 K and a dynamic exponent zv = ∼7.3. The SG nature is further corroborated from chaos and memory effects, magnetic hysteresis, and aging behavior. We discuss the results in terms of the competition among random magnetic anisotropy and exchange interactions and compare them with simulation predictions.

Dependences of microwave surface resistance of HTS thin films on applied dc magnetic fields parallel and normal to the substrate

We investigated the dc magnetic field and temperature dependences of microwave surface resistance (Rs) of high-temperature superconductor (HTS) films. Previously, we reported that the surface resistance RsRs(n) under a dc magnetic field applied normaly to the substrate increased when increasing the applied magnetic field. For NMR application, we have to examine the Rs(p) under the dc magnetic field parallel to the substrate. We measured the Rs(p) of the YBCO and DyBCO thin films with a thickness of 500 nm deposited on a MgO (100) substrate using the dielectric resonator method at 21.8 GHz, and a dc magnetic field of up to 5 T. In a zero magnetic field, the values of Rs(n) and Rs(p) were 0.35 mQ at 20 K. Under the dc magnetic field, the Rs(n) and the Rs(p) also increased with increasing magnetic field, however, the Rs(p) had a lower magnetic field dependence and the value was about 1/10 of that of the Rs(n). The Rs(p) at 16.4 T and at 700 MHz could be estimated by the two-fluid model. The Rs(p) value was about 1/2600 compared with that of copper at 20 K. As a result, we clarified that 500 nm thick YBCO and DyBCO thin films could provide advantages for NMR application.

Microwave surface resistance of YBCO superconducting thin films under high DC magnetic field

We investigated the dc magnetic field and temperature dependences of the microwave surface resistance (Rs) of YBa2Cu3Oy (YBCO) superconducting thin films with various thicknesses. We used YBCO thin films with 300, 500, and 700nm deposited on a MgO (100) substrate by the thermal co-evaporation method. The Rs was measured using the dielectric resonator method at 21.8GHz, and a high dc magnetic field of up to 12T was applied parallel to the c-axis of the YBCO thin films during Rs measurements. The Rs value of YBCO thin films increased when dc magnetic field was applied. These relationships could be explained by using the two-fluid model for high frequency and low magnetic field limits. We defined the viscous drag coefficient η under the low magnetic limit and the high magnetic field limit as the ηlow (B, T, d) and ηhigh (B, T, d), respectively. The ηlow values were approximately two orders of magnitude greater than ηhigh values. Also, all ηlow and ηhigh value decreased or saturated as the temperature and film thickness increased. These results show that η under the low and high magnetic field limit depended on the temperature and film thickness.

Magnetic and electrical transport properties in the self-doped manganite La0.9Mn0.9M0.1O3 (M=Mn, Zn and Ti)

The magnetic and electrical transport properties of La0.9Mn0.9M0.1O3 (M=Mn, Zn and Ti) were investigated. The temperature and magnetic field dependence of electrical resistivity (ρ) and dc magnetization were studied. All the compounds are found in rhombohedral structure. The excess oxygen in all three compounds was detected through iodometric titration. A modification in resistivity is observed when M=Mn is replaced by M=Zn and Ti. The high temperature resistivity above TC follow variable range hopping model for both Zn and Ti compounds. For Zn doping, the observation of large field-cool effect and decrease in resistivity at room temperature and is assumed to be due to the implant of Mn4+ in Mn3+ matrix, which favor Mn3+/Mn4+ double exchange. The ferromagnetic behavior below TC for the compound with M=Ti is correlated to the excess oxygen in it, which implants Mn4+ and thus incorporates ferromagnetic interactions. The substitutions lead to a reduction of Tc and magnetization.

The nature of the magnetism in quasi-2D layered α-Ni(OH)2

The two layered hexagonal hydroxides of Ni are β-Ni(OH)2 and α-Ni(OH)2; β-Ni(OH)2 is now known to be an antiferromagnet whereas the nature of the magnetism in α-Ni(OH)2 is not yet well established. Here, the magnetic properties of α-Ni(OH)2 with lattice parameters a = 3.02 Å and c = 8.6 Å, and flower-like morphology with petal thickness of ≃ 50 Å are reported. Temperature (2–300 K) and magnetic field (up to 65 kOe) dependence of the magnetization and ac susceptibility at f = 0.1–1000 Hz were measured. Analysis of the data yields ferromagnetic ordering in the system with TC ≃ 16 K. In addition, a nanosize related blocking temperature TB = 8 K and spin-glass-like ordering of the surface spins near 3.5 K are inferred from the ac frequency and dc magnetic field dependence of these transitions. Fitting to the high temperature series and quasi-2D nature of the system is used to determine J1/kB = 4.38 K (J2/kB = 0.14 K) for the intraplane (interplane) exchange coupling between the Ni2+ ions.

Ferroelectricity, ferromagnetism, and magnetoelectric coupling in highly textured thin films of the multiferroic Pb(Fe0.5Nb0.5)O3

ABSTRACTA study of the ferroelectric and magnetic properties and of the magnetoelectric coupling effects of Pb(Fe0.5Nb0.5)O3 (PFN) thin films, grown on SrRuO3/Si [(100) or (111)] substrates by the rf-magnetron sputtering technique, is presented. Structural, morphological, and compositional characterization was realized using the XRD, AFM, XPS, and TEM techniques. Highly textured single phase films with different thickness (from 45 to 270 nm) were successfully grown without Fe2+ presence. A vertically [110] oriented grainy structure was observed. Polarization vs. electric field (P-E) hysteresis loops exhibit excellent and almost constant values of the maximum (∼ 60 μC/cm2) and remanent (∼ 22 μC/cm2) polarizations in the temperature range from 4 K to room temperature; small values of the coercive field, characteristic of soft ferroelectric materials, are observed in these samples. Measurements of the zero-field cooled (ZFC) and field cooled (FC) magnetization behavior and magnetic (M-H) hysteresis loops were realized at different temperatures between 5 and 300 K. Proof of the existence of ferromagnetic order in the low temperature region (below to 50 K) is discussed and reported for the first time. Values of the maximum (∼ 3 emu/g) and remanent (∼ 1.5 emu/g) magnetizations were obtained. dc magnetic field dependence of the ferroelectric hysteresis loops are shown as evidence of the magnetoelectric coupling.

Intrinsic Surface Resistance of YBCO Thin Films Under DC Magnetic Field

We investigated the dc magnetic field and temperature dependences of the microwave intrinsic surface resistance (Rsint) of YBa2Cu3Oy (YBCO) superconducting thin films with various thicknesses. We used YBCO films from 100, 200, and 300 nm thick YBCO films deposited on CeO2/Al2O3 substrates. The Rsint is means the surface resistance of YBCO film without the dielectric loss of the substrates. The Rsint was obtained from measured surface resistance (Rs) by using a phenomenological equation. The Rs was measured using the dielectric resonator method at 21.8 GHz. A dc magnetic field of up to 5.0 T was applied parallel to the c-axis of the superconducting thin films during the Rs measurements. The Rsint of the YBCO thin films increased when the dc magnetic field was applied. These relations could be explained with the two-fluid model for high-frequency and high-magnetic field limits. The Rsint ratio (defined as Rsint (5T)/Rsint (0T)) slightly decreased with the film thickness. These results indicate that the Rsint of HTS films depends on the film thickness in the dc magnetic field and the Rsint in a dc magnetic field may be related to the pinning center in the HTS films.

The dc magnetic field, temperature and film thickness dependence of microwave surface resistance of YBCO and DyBCO thin films

We investigated the dc magnetic field and temperature dependences of the microwave surface resistance (Rs) of YBa2Cu3Oy (YBCO) and DyBa2Cu3Oy (DyBCO) superconducting thin films. The YBCO and DyBCO thin films, each with a thickness of 300, 500, or 700nm, were deposited on MgO (100) substrates by the thermal co-evaporation method. The Rs was measured using the dielectric resonator method. A dc magnetic field of up to 5.0T was applied parallel to the c-axis of the superconducting thin films. The results showed that the Rs value had almost the same temperature dependence at various thicknesses in a zero-external field. The Rs of the YBCO and DyBCO thin films increased with the applied dc magnetic field. The DyBCO thin films showed weaker magnetic field dependence of Rs than the YBCO thin films. The Rs ratio (defined as Rs(5T)/Rs(0T)) linearly increased with the film thickness. These results show that pinning strength decreased with an increasing film thickness.

Dynamic properties of cluster glass in La0.25Ca0.75MnO3 nanoparticles

The dynamic magnetic properties of cluster glass in La0.25Ca0.75MnO3 nanoparticles with average particle size range from 40 to 1000 nm have been investigated by measuring the frequency and dc magnetic field (H) dependencies of the ac susceptibility. The frequency-dependent Tf, the freezing temperature of the ferromagnetic clusters determined by the peak in the real part of the ac susceptibility χ′ versus T curve with H=0, is fit to a power law. The relaxation time constant τ0 decreases as the particle size increases from 40 to 350 nm, which indicates the decrease in the size of the clusters at the surface of the nanoparticle. The relationship between H and Tf(H) deviates from the De Almeida–Thouless-type phase boundary at relatively high fields for the samples with size range from 40 to 350 nm. Moreover, for the samples with particle sizes of 40 and 100 nm, τ0 increases with increasing H, which indicates the increasing cluster size and may be ascribed to the competition between the influence of H and the local anisotropy field in the shell spins. All these results may give rise to a new insight into the behaviors of the cluster glass state in the nanosized antiferromagnetic charge-ordered perovskite manganites.

Properties, magnetic susceptibility, critical currents and irreversibility fields of(Tl0.5Pb0.5)Sr2 (Ca1−xGdx)Cu2Oz bulk superconductors

Bulk (Tl0.5Pb0.5)Sr2(Ca1−xGdx)Cu2Oz superconductors with x = 0.1,0.2 and 0.3 were prepared by a wet chemical gel technique followed by aspecial heat-treatment procedure. X-ray diffraction analysis revealedpractically phase-pure samples with tetragonal structure (space groupP/4mmm). The temperature dependence of the real and imaginary parts of the acsusceptibility and the dependence on the ac applied magnetic field wereinvestigated to learn about the superconducting and magnetic properties of bulk(Tl0.5Pb0.5)Sr2(Ca1−xGdx)Cu2Oz superconductors. The critical current densities of the samples were derived from Bean’smodel. The temperature dependence of the critical current was successfully fitted basedon a power law from the thermally activated magnetic flux creep model. Frommagneto-resistance measurements the temperature dependences of the transport criticalcurrents and the irreversibility fields were found. The dc magnetic field dependence of thewidth of superconducting transitions and the critical currents was also obtained. Theseproperties of the superconductors were analyzed within available theoretical models.

Frequency-dependent electromagnetic properties of the Pb-doped manganite measured in the transformer-type circuit

The dependence of the transformation coefficient of the four-pole network with the toroid core made of the La 0.6Pb 0.4MnO 3 manganite on dc biasing magnetic field and frequency was experimentally investigated. The factors which influence the value of the transmission coefficient are analyzed. In the megahertz frequency range the frequency dependence of the transformation coefficient has a resonant form with the position of the maximum and amplitude increasing with the dc biasing. The dc magnetic field dependence of the phase shift between the voltages in the primary and secondary windings was investigated. The results are interpreted taking into account the imaginary component of magnetic permeability of the core material.

Comparative Analysis of the Fundamental Susceptibility in Bi-2212 Single Crystal

The temperature and field dependencies of the fundamental susceptibilities have been measured to study the vortex dynamics in Bi-2212 single crystal. The model incorporating both the concepts of collective creep and critical state has been used to explain amplitudes of the ac magnetic field and frequency with combination of dc magnetic field and temperature dependencies of the susceptibilities. The comparison performed between the results obtained from the measurements and the model calculations shows that a good agreement between them exists.