Zero-field-cooled Research Articles

Creep effects on the Campbell response in type-II superconductors

Applying the strong pinning formalism to the mixed state of a type II superconductor, we study the effect of thermal fluctuations (or creep) on the penetration of an ac magnetic field as quantified by the so-called Campbell length $\lambda_\textrm{C}$. Within strong pinning theory, vortices get pinned by individual defects, with the jumps in the pinning energy ($\Delta e_\mathrm{pin}$) and force ($\Delta f_\mathrm{pin}$) between bistable pinned and free states quantifying the pinning process. We find that the evolution of the Campbell length $\lambda_{\rm C}(t)$ as a function of time $t$ is the result of two competing effects, the change in the force jumps $\Delta f_\mathrm{pin}(t)$ and a change in the trapping area $S_\mathrm{trap}(t)$ of vortices; the latter describes the area around the defect where a nearby vortex gets and remains trapped. Contrary to naive expectation, we find that during the decay of the critical state in a zero-field cooled (ZFC) experiment, the Campbell length $\lambda_{\rm C}(t)$ is usually nonmonotonic, first decreasing with time $t$ and then increasing for long waiting times. Field cooled (FC) experiments exhibit hysteretic effects in $\lambda_\textrm{C}$; relaxation then turns out to be predominantly monotonic, but its magnitude and direction depends on the specific phase of the cooling--heating cycle. Furthermore, when approaching equilibrium, the Campbell length relaxes to a finite value, different from the persistent current which vanishes at long waiting times $t$, e.g., above the irreversibility line. Finally, measuring the Campbell length $\lambda_\textrm{C}(t)$ for different states, zero-field cooled, field cooled, and relaxed, as a function of different waiting times $t$ and temperatures $T,$ allows to spectroscopyse the pinning potential of the defects.

Effect of chromium substitution on the electrical and magnetic properties of multiferroic yttrium manganite

Yttrium Manganite is a multiferroic material and has potential applications in Ferroelectric Random Access Memories. Chromium is substituted with a view to enhancing the electrical conductivity. Compositions belonging to the series Y1−xCrxMnO3, (x = 0, 0.05, 0.1, and 0.3) were synthesized by employing a citrate gel method. Pre characterized samples using X-ray diffraction and Scanning Electron Microscopy were then subjected to impedance spectroscopy to understand the conduction mechanism vis-à-vis small polaron hopping or variable range hopping. Cole-Cole and Nyquist plots were utilized to arrive at the equivalent circuit. Ferroelectric measurements were carried out to understand the polarization mechanisms. Magnetic measurements were also conducted to observe the change in magnetic properties with Chromium substitution. Field Cooled (FC) and Zero Field Cooled (ZFC) magnetization measurements revealed the presence of ferromagnetic clusters in an antiferromagnetic matrix. It has been found that Chromium substitution enhances the electrical conductivity while it diminishes the ferroelectric properties.

Air-Stable Dy(III)-Macrocycle Enantiomers: From Chiral to Polar Space Group

Air-Stable Dy(III)-Macrocycle Enantiomers: From Chiral to Polar Space Group

Investigation of structural, magnetic, and electrical properties of Ru doped brownmillerite oxide: KBiFe2O5

We studied and reported the Ruthenium (Ru) doped KBF (KBiFe2O5) multiferroic nanoparticles on structurl, magneitc and electrical properites as a function of dopant and temperature, synthesized through coprecipitation route. X-ray Diffraction spectra of all the samples were indexed with orthorhombic structure (space group P21am) at room temperature and lattice constant decreased with Ru substition. The structural parameters including bond lengths and angles were refined using a standard Rietveld program. Average crystallite measured from schereer method increases with increasing annelaing temperature. Morphology from TEM confirms control over uniform distribution of particle size and shape. Zero field-cooled (ZFC)-Field-Cooled (FC) magnetic measurements reveals superparamagnetic behaviour above room temperature. Magnetic hysteresis loops (M − H) measured at 5 K and 300 K shows improvement with Ru substitution. An insginificant decrease in optical band gap 2.35 to 2.23 eV observed from UV–Vis spectroscopy with Ru substitution. Ferroelectric loops resembling lossy dielectric nature of unpoled samples. Activation energy estimated from DC electrical resistivity was found to be 0.6 eV. Room temperature Dielectric data revelas Maxwell-Wanger type dielectric dispersion and analyzed based on the intrinsic and extrinsic parameters.

Interesting magnetic response of the nuclear fuel material UO2

ABSTRACT We report results of dc magnetization measurements on UO2. Our study reveals a deviation from standard Curie-Weiss (CW) paramagnetic behavior below 280 K, and that is followed by a transition to antiferromagnetic state with marked thermomagnetic irreversibility below TN = 30.6 K. The zero field cooled (ZFC) magnetization exhibits distinct structures not usually observed in the antiferromagnets, whereas field cooled (FC) magnetization looks more like a ferromagnet. The thermomagnetic irreversibility continues to exist in a subtle way even in the paramagnetic regime well above TN . This behavior along with the deviation from CW law highlight non-standard nature of the paramagnetic state. Magnetic response below TN changes significantly with the increase in the applied magnetic field. In the isothermal magnetic field variation of magnetization, a subtle signature of a magnetic field-induced phase transition is observed. All these experimental results highlight the non-trivial nature of the magnetic state in UO2.

Synthesis and magnetic characterizations of [formula omitted] solid solution with [formula omitted] 0.016 as a new low – dimensional dilute magnetic - semiconductor material

In this study, TlInS2 layered semiconducting compound in which In3+ ions were partially substituted by ∼ 1.6 %Fe3+ transition metal ions was prepared by means the Bridgman – Stockbarger technique. The crystal structure of TlIn1-xFexS2 with x= 0.016 in combination with magnetization dynamics and magnetic resonance measurements have been studied. Energy dispersive X-ray (EDX) spectrum of Fe – substituted TlInS2 compound confirms the presence of all the constituent elements in stoichiometric proportions. We concluded that the magnetic properties of TlIn1-xFexS2 were induced by substituting trivalent iron atoms in the place of In3+ ion sites located at the center of In3+S42- structural units of TlInS2 crystal. EPR study reveals that the local site symmetry around Fe3+ center is orthorhombic. The orthorhombic local symmetry can be considered to originate crystal field arising from Tl ligands in the trigonal cavities surrounding Fe3+ transition metal ion. The angular dependence resonance lines show that the crystal lattice contain two structurally equivalent Fe3+ centers localized at different tetrahedron arrays of crystal structure. The temperature dependences of the magnetization measured in the zero - field cooling (ZFC) and field cooling (FC) regimes in the magnetic field of ∼ 50 Oe is found to correspond to a paramagnetic behavior at low temperatures. It has been founded that Fe moments in the TlInS2 host lattice can be ordered to ferromagnetic – like structure. This conclusion in magnetic behavior of TlIn1-xFexS2 compound is well - justified by the existence of very narrow hysteresis loops in the field dependent magnetization curves. Thus, in this work we propose that Fe – diluted TlInS2 is a new and promising dilute magnetic semiconductor with a large potential for future spintronic applications.

Temperature-dependent magnetodielectric, magnetoimpedance, and magnetic field controlled dielectric relaxation response in KBiFe2O5

In this work, polycrystalline KBiFe2O5 (KBFO), belonging to the brownmillerite class of monoclinic structure with space group P2/c, is synthesized using a solid-state reaction route. Magnetodielectric (MD) and magnetoimpedance (MI) characteristics of KBFO are studied over a wide temperature (10–300 K), magnetic field (0–1.3 T), and frequency (100 Hz to 1 MHz) range. Zero-field-cool (ZFC) and field-cool (FC) magnetization data show a bifurcation around 11 K, indicating blocking temperature (TB). At room temperature, MD and MI data as a function of the magnetic field shows maximum MD and MI coupling to be ∼−0.6% and ∼0.7%, respectively, at 50 kHz. With the decrease in temperature from 300 K to 50 K, magnetodielectric strength decreases (−0.6% to −0.06%), whereas magnetization increases from canted-antiferromagnetic (MS ≈ 0.16 emu g−1) to a weak ferromagnetic state (MS ≈ 0.44 emu g−1). It indicates the existence of Inverse Dzyaloshinskii-Moriya interaction causing MD coupling in KBFO. MD behavior is also reflected in magnetic field-dependent dielectric relaxation phenomena demonstrated through magnetic field-dependent activation energies. The difference in activation energies of magnetic field-dependent conduction mechanism (Eg ≈ 0.370 ± 0.018 eV) and MD loss relaxation (Eg ≈ 0.183 ± 0.006 eV) indicate both have a different origin. The presence of the capacitive MI effect demonstrates that the observed magnetodielectric coupling is intrinsic. The existence of both temperatures-dependent MD and MI coupling in KBFO makes it suitable for dynamic random access memory as well as novel magnetic sensors.

Structural, magnetic and optical properties of (0.45) Ni0.5Zn0.5Fe2O4 + (0.55) BaFe12O19 composite

The magnetic composite of (45%) (NZF ,Zn0.5Ni0.5Fe2O4) and (55%) (BHF, BaFe12O19) has been prepared by the physical mixing method. The structural, optical, and magnetic properties have been studied by using XRD (X-ray diffraction), UV–Vis spectroscopy, and VSM (Vibrating sample magnetometer), respectively. The XRD patterns have confirmed the presence of both crystal symmetries (BHF and NZF) without any extra phases within the XRD limit. The magnetic hysteresis loops were traced at different measuring temperatures (60–300 K). The increment of saturation magnetization (Ms) with the decrease in temperature is due to the reduction of magnetic Gibb’s free energy. The kinks in the M−H loops reveal the presence of magnetic biasing between NZF and BHF. The presence of magnetic biasing is analyzed by the plot of loop width (ΔH) with magnetization (M). If a hump is observed in ΔH ∼ M plot, this gives evidence of magnetic biasing. The M−T plots in field cooled (FC) and zero field cooled (ZFC) conditions were traced at the applied magnetic field of 0.5 kOe in the temperature range of 400–60 K. The band gap has been obtained by the UV–Vis analysis.

Optimization of the Guiding Stability of a Horizontal Axis HTS ZFC Radial Levitation Bearing

This document presents a study on the optimization of the 3D geometry of a horizontal axis radial levitation bearing with zero-field cooled (ZFC) high-temperature superconductor (HTS) bulks in the stator, and radially magnetized permanent magnet (PM) rings in the rotor. The optimization of component dimensions and spacing to minimize the volume or cost concerning only the maximization of the levitation force was previously studied. The guidance force and guiding stability depend on the spacing between PM rings in the rotor and between the rings of HTS bulks in the stator. This new optimization study aims to find the optimum spacing that maximize the guidance force with given HTS bulk and PM ring dimensions while maintaining the minimum required levitation force. Decisions are taken using the non-dominated sorting genetic algorithm (NSGA-II) over 3D finite element analysis (FEA). A simplified electromagnetic model of equivalent relative permeability is used on 3D FEA to reduce numerical processing and optimization time. Experimental prototypes were built to measure magnetic forces and validate appropriate values of equivalent magnetic permeability. An analysis of stable and unstable geometry domains depending on the spacing between rings of HTS bulks and PM rings is also done for two HTS bulk sizes.

Evidence for increased metallicity arising from carbon-sulfur bonding and amorphization effects in sulfur-doped pyrolytic graphite

We report a novel investigation of the electronic and magnetic properties of exfoliated lamellae of highly-oriented-pyrolytic-graphite (HOPG) doped with great excess of sulfur. The sulfur-doping process was achieved through annealing at T ~ 250 °C, ~500 °C and ~990 °C. The obtained lamellae were investigated by employing transmission electron microscopy (TEM), Raman point/map spectroscopy and temperature dependent electron paramagnetic resonance (T-EPR). HRTEM analyses of samples doped at T ~ 990 °C revealed an unusual amorphization-effect arising within hexagonal moiré superlattices as a consequence of the sulfur-doping. Complete amorphization was found at T ~ 500 °C. Raman-spectroscopy point/mapping analyses highlighted a dominant carbon-sulfur-band, appearing at Raman-Shifts of 1450 cm−1. T-EPR of heavily doped samples revealed presence of shifts in the position of the π-electron differential absorption feature together with an anomalous signal broadening at Tdoping ~ 500 °C (from g ~ 1.99 to g ~ 2.10), while zero field cooled (ZFC) and field cooled FC superconducting quantum interference device (SQUID) magnetometry from 2 K to 300 K revealed a critical percolative ferromagnetic temperature at T ~ 25 K and the absence of superconductive transitions. Density functional theory (DFT) calculations applied to a Bernal (AB stacked) bilayer-graphene-system in presence of sulfur-bonding revealed a significant variation of the system-metallicity. We highlight the appearance of insulating states (E-gap of 0.325 eV) at sulfur concentrations of ~1%, which then vanish at ~5.5% of sulfur-doping, due to an enhanced degree of system-metallicity and a modification of the π-bonding- and antibonding-signals.

Preparation of PSFO and LPSFO nanofibers by electrospinning and their electronic transport and magnetic properties

Pr0.5Sr0.5FeO3 (PSFO) and La0.25Pr0.25Sr0.5FeO3 (LPSFO) nanofibers are prepared by electrospinning followed by calcination, and their morphologies, microstructures, electronic transports, and magnetic properties are studied systematically. The temperature-dependent resistance curves of PSFO and LPSFO nanofibers are measured in a temperature range from 300 K to 10 K. With the temperature lowering, the resistance increases gradually and then decreases sharply due to the occurrence of ferromagnetic metal phase. The metal–insulator transition temperatures are about 110 K and 180 K for PSFO and LPSFO nanofibers, respectively. The electronic conduction behavior above the transition temperature can be described by one-dimensional Mott’s variable-range hopping (VRH) model. The hysteresis loops and the field-cooled (FC) and zero-field-cooled (ZFC) curves show that both PSFO nanofiber and LPSFO nanofiber exhibit ferromagnetism. Although the doping of La reduces the overall magnetization intensity of the material, it increases the ferromagnetic ratio of the system, which may improve the performance of LPSFO in solid oxide fuel cell.

Negative zero‐field‐cooled magnetization and magnetic switching in multiferroic Lu0.5Sc0.5FeO3 ceramics

AbstractIn this study, we have investigated the negative magnetization of Lu0.5Sc0.5FeO3 (LSFO) ceramics in the zero‐field‐cooled (ZFC) mode. The negative magnetization in ZFC measurement appears below the Neél temperature (TN) in LSFO, which is probably caused by the residual negative trapping field in superconducting magnet, and is closely related to the giant coercivity in LSFO. By fitting the high‐temperature paramagnetic data under nominal zero magnetic field, the negative trapping field in superconducting magnet is found to be −3.28 Oe. The giant coercivity is ascribed to the strong uniaxial magnetocrystalline anisotropy in LSFO, which can cause the strong magnetic domain wall pinning effect to limit the nucleation of reversed domains under reverse field. In addition, a switchable magnetization switching is realized in LSFO. The magnetization of LSFO can stably switch between positive and negative values when the applied magnetic field was switched between 0.5 and 3 kOe, which suggests that the LSFO samples are suitable for potential applications in magnetic storage.

Negative differential resistance state in the free-flux-flow regime of driven vortices in a single crystal of 2H−NbS2

Time series measurements [G. Shaw et al., Phys. Rev. B 85, 174517 (2012); B. Bag et al., Sci. Rep. 7, 5531 (2017)] in $2H\text{\ensuremath{-}}{\mathrm{NbS}}_{2}$ crystal had unraveled a drive-induced transition wherein the critical current $({I}_{c})$ changes from a low to a high ${I}_{c}$ jammed vortex state, via a negative differential resistance (NDR) transition. Here, using multiple current-voltage $(I\text{\ensuremath{-}}V)$ measurement cycles, we explore the statistical nature of observing the NDR (or a quasi-NDR in reversing $I$ measurements) transition in the free-flux-flow (FF) regime in a single crystal of $2H\text{\ensuremath{-}}{\mathrm{NbS}}_{2}$. Prior to the occurrence of the NDR transition, the pristine full $I\text{\ensuremath{-}}V$ curve exhibits a featureless smooth depinning from the low ${I}_{c}$ state. With subsequent current cycling, the NDR transition appears in the $I\text{\ensuremath{-}}V$ curve. Post-NDR, the full $I\text{\ensuremath{-}}V$ curve is seen to be noisy with depinning commencing from the higher ${I}_{c}$ state. The probability of observing the NDR transition always remains finite for a vortex state created with either fast or slow rate of magnetic field, $\stackrel{\ifmmode \dot{}\else \.{}\fi{}}{B}$. The probability of observing the NDR transition in the FF regime is found to systematically increase with magnetic field $(B)$ in weak collective pinning regime. In the strong pinning regime, the said probability becomes field independent. Retaining of a nonzero probability for the occurrence of the NDR transition under all conditions, the observed new data shows that the $I\text{\ensuremath{-}}V$ branch with higher ${I}_{c}$ is the more stable compared to the lower ${I}_{c}$ branch. We show that the higher ${I}_{c}$ state, generated via the NDR transition, is unique and cannot be accessed via any conventional route, in particular, by preparing the static vortex state with a different thermomagnetic history. While the $I\text{\ensuremath{-}}V$ curves do not distinguish between zero field cooled (ZFC) and field cooled (FC) modes of preparing the vortex state, the probability for observing an NDR transition has different $B$ dependences for the vortex matter prepared in the ZFC and FC modes. We find that the NDR transition occurs in a high dissipation regime, where the flow resistivity is well above the theoretical value expected in the FF regime. We understand our results on the basis of a rapid drop in vortex viscosity at high drives in $2H\text{\ensuremath{-}}{\mathrm{NbS}}_{2}$, which triggers a rapid increase in the vortex velocity and reorganization in the moving vortex matter leading to a dynamical unstable vortex flow. This dynamical instability leads to the NDR transition into a high entropy vortex state with high ${I}_{c}$.

Physical and magnetic properties of frustrated triangular-lattice antiferromagnets R3Cu (R = Ce, Pr)

We report the synthesis, crystal structure, and thermodynamic properties of the two binary laves phases Ce3Cu and Pr3Cu, which crystallize in the tetragonal I4/mmm (space group: 139). We have investigated the compounds using dc magnetic susceptibility χdc(T), ac magnetic susceptibility χac(T), isothermal magnetization M(B) and specific heat Cp(T) measurements. Both compounds show features of strong geometrical frustration, which is driven by the arrangement of the rare-earth ions on triangular lattice sites. Ce3Cu shows a phase transition at TN = 5 K and its M(B) at 2 K reveals the presence of a metamagnetic transition near 2 T. Pr3Cu, on the other hand, shows a spin-glass behaviour with a freezing temperature of Tf1 ≃ 12 K and with an irreversible behavior in zero-field-cooled (ZFC) and field-cooled (FC) χdc(T) below about 13 K. The real part of χac(T) reveals a frequency dependence of Tf. The result, however shows the presence of another frequency-dependent phase below Tf2 ≃ 9.35 K, a feature which signals a re-entrant spin-glass behaviour in the compound. Furthermore, the frequency dependence of Tf1 follows the Vogel-Fulcher law, with an activation energy Ea∕kB = 5.3 K. This observation along with the estimated relative shift in Tf1 per decade in frequency δTf = 0.0105, irreversible behaviour in ZFC-FC χdc(T) and a slow decay in thermo-remnant magnetization provide supports for the formation of a cluster spin-glass in Pr3Cu. In addition, we observe the enhancement of the Sommerfeld coefficient, γ in both compounds with values of 0.1892(5) J/(molCe K2) and 0.5078(1) J/(molPr K2). The estimation of the Sommerfeld-Wilson ratio WR yield values of 0.576 and 1.17 for Ce3Cu and Pr3Cu, respectively.

The Highly Frustrated 5d2 Double Perovskite Doppelgängers, SrLaMgReO6 and SrLaLiOsO6. A Comparison including Isostructural La2LiReO6.

The synthesis and characterization of the double perovskite SrLaLiOsO6 is presented. It is isostructural (P21/n) and isoelectronic (5d2) with SrLaMgReO6, which has been reported previously. The cell volumes are the same to within 1.4%: i.e., these perovskites are doppelgängers. In a previous study SrLaMgReO6 showed no sign of spin order to 2 K. New data at lower temperatures disclose a maximum in the dc susceptibility near 1.5 K. As the Curie-Weiss (C-W) temperature (Θ) for this material is -161 K, an enormous frustration index, f ≈ 100, is implied (f = |Θ|/Tord). On the other hand, SrLaLiOsO6 does not follow the C-W law over the investigated susceptibility range, 2-300 K. Fitting with an added temperature independent term (TIP) gives μeff = 1.96 μB, Θ = -102 K, and TIP = 1.01 × 10-3 emu/mol. A clear zero-field-cooled (ZFC), field-cooled (FC) divergence in the dc data occurs at ∼10 K, suggesting a much reduced frustration index, f ≈ 10, relative to SrLaMgReO6. The real part of the ac susceptibility data, χ'max, shows a frequency shift that is consistent with a spin glass ground state according to the Mydosh criterion. Heat capacity data for SrLaLiOsO6 show no sign of a λ peak at 10 K and a linear dependence on temperature below 10 K, also supporting a spin glass ground state. A spin frozen ground state for SrLaMgReO6 could not be established from χ' data due to a much weaker signal. Nonetheless, the 10-fold difference in f between these doppelgänger materials is remarkable. It is possible that the enhanced covalency with the oxide ligands for Os6+ relative to Re5+ plays a major role here. Finally, a comparison with isostructural La2LiReO6 (with a much smaller f ≈ 4) is made and a correlation between the frustration level and the sense of the local distortion of the Re(Os)-O octahedron is pointed out.

Spin–glass behavior in Shastry–Sutherland lattice of Tm[formula omitted]Cu[formula omitted]In

The spin–glass behavior in the ferromagnetic phase of Tm2Cu2In was investigated by dc–, ac–magnetization, and non-equilibrium dynamics characterizations. An argon arc–melted polycrystalline sample of the compound of Tm2Cu2In was found to adopt the Mo2FeB2–type tetragonal structure (space group P4/mbm). The temperature variation of dc–magnetization exhibits a ferromagnetic behavior with Curie temperature TC = 32.5 K. The zero field cooled (ZFC) and field cooled (FC) magnetic curves show the thermomagnetic irreversible behavior below TC. The field dependence of irreversible temperature follows the Almeida–Thouless line. The frequency and ac–driven field dependent anomalies in ac–susceptibility results indicate the existence of a spin–glass state in Tm2Cu2In. The time dependence of magnetization further supports the spin–glass behavior observed in Tm2Cu2In. The frequency dependence of the freezing temperature in the real part of ac–susceptibility has been analyzed on the basis of a power–law divergence and Vogel–Fulcher law. The obtained results reveal that Tm2Cu2In belongs to the ferromagnetic canonical spin–glass class of compounds.

Lead free single – double perovskite composite towards room temperature multiferroicity

Lead free BaTiO3-La2NiMnO6 (BTO-LNMO) composite sample was prepared via solid-state sintering route. Structural studies based on X-ray diffraction (XRD) patterns indicate BTO and LNMO each retain their respective structure in composite form. Raman spectra of composite inferred no structural modulation after mixing of individual phases of BTO and LNMO. The change in microstructure is observed for composite due to the difference in thermal expansion coefficient as well as the different rate of grain growth of BTO and LNMO phases. BTO-LNMO composite sample is found to be ferromagnetic with non saturation of magnetic moments. Temperature-dependent zero-field cooled (ZFC) and field cooled (FC) curves show large irreversibility (94%) for composite than the pure LNMO phase. The magnetic Curie temperature (Tc) of the composite was observed near room temperature. The dielectric and ferroelectric features of BTO is well maintained in composite at room temperature. This study is an attempt to bring in the multiferroicity (magnetic and ferroelectric order simultaneously) in the proximity of room temperature by incorporating the small percentage of magnetic phase (LNMO) in the ferroelectric (BTO) matrix.

Studies on superparamagnetic behaviour of Ni100-xCux alloy films deposited by DC magnetron sputtering

ABSTRACT In this study, nanocrystalline Ni100-xCux alloy films have been synthesised using DC magnetron co-sputtering under argon gas atmosphere to analyse their superparamagnetic behaviour. The nanocrystalline nature and the grain size of the alloy films have been measured using grazing incidence x-ray diffraction (GIXRD) and a transmission electron microscopy (TEM). The M-H curves obtained using superconducting quantum interference device provides evidence for superparamagnetic behaviour of the nanocrystalline Ni100-xCux alloy films. For the Ni89Cu11 alloy films, the highest value (456 emu/cm3) of saturation magnetisation has been measured. Zero field cooling (ZFC) and field cooling (FC) data obtained from superconducting quantum interference device (SQUID) showed the dependence of blocking temperature, TB on Cu concentration of the investigated NiCu alloy. The blocking temperature is observed to decrease from 44 K to 33 K with increase in Cu concentration from 11 to 28 wt%.

Memory effect in Fe-Ag granular multilayers

Magnetic memory effect was measured in Fe-Ag granular multilayers by employing the so-called stop-and-wait protocol in order to reveal super-spin glass (SSG) behavior and explore the role of intra- and interlayer interactions which can influence the superparamagnetic (SPM) behavior of Fe particles separated by Ag layers. Calculations based on the relaxation of two-level systems are made to obtain the evolution of the magnetization of interaction-free SPM particles as a function of temperature and time for arbitrary annealing procedures, e.g., zero-field-cooled (ZFC) and field-cooled (FC) susceptibility (low-field magnetization) or temperature-cycling measurements. In samples with a single Fe layer of different nominal thicknesses, both the observed memory effect and the low-temperature deviation of the measured FC magnetization from the calculated interaction-free FC curve are attributed to the effect of dipolar interactions. Estimates on the anisotropy energy suggest the importance of the surface anisotropy of the Fe particles in the magnetic behavior.

SnAs: A 4K weak type-II superconductor with non-trivial band topology

Superconductors with non-trivial band topology are emerging as one of the best avenues to study quantum anomalies and experimental realization of Majorana Fermions. This article reports the successful crystal growth of superconducting SnAs, which can have topologically non-trivial states, as evidenced in DFT (Density Functional Theory) calculations, Z2 invariants and topological surface states. Here, we followed a two-step method to grow SnAs crystal. The powder XRD (X-ray Diffractometry) pattern of synthesized crystal ensures that the crystal is grown in a single phase with a NaCl type cubic structure and the EDAX (Energy Dispersive X-ray Analysis) endorses the stoichiometry of the as-grown sample. The DFT calculations performed with and without inclusion of spin-orbit coupling (SOC) show band inversion at various k symmetry points near the Fermi level. The recorded Raman spectra show two different modes, which are assigned as A1 and ETO vibrations. The ZFC (Zero-Field Cooled) & FC (Field Cooled), as well as the isothermal M − H (Magnetization vs. field) measurements, are also performed for the topological non-trivial SnAs superconductor, which eventually confirm the weak type-II superconductivity at 4K. Various other superconductivity parameters viz. kappa parameter, coherence length, and penetration depth are also calculated to probe the as-grown sample's characteristics.