Ac Susceptibility Measurements Research Articles

Biaxially textured (Bi, Pb)2Sr2Ca2Cu3Ox thin films on LaAlO3 substrates fabricated via the chemical solution deposition method

In this study, biaxially textured (Bi, Pb)2Sr2Ca2Cu3Ox ((Bi, Pb)-2223) thin films were fabricated epitaxially on LaAlO3 (LAO) single crystal substrates via the chemical solution deposition (CSD) method. In order to prevent the evaporation of Bi and Pb, a sealed face-to-face architecture for sintering was utilized. According to the results of x-ray diffraction measurements including θ/2θ-scan, ω-scan, and ϕ-scan patterns, the optimal sintering temperature was found to be 840 °C. The volume fraction of the (Bi, Pb)-2223 phase of the optimal sample was enhanced to above 80%. Favorable out-of-plane and in-plane textures were also detected, which could be attributed to an epitaxy system of (Bi, Pb)-2223 thin film and an LAO substrate with a 45° rotated alignment. A dense microstructure and thickness of about 100 nm were found by scanning electron microscopy observations of the surface morphology and cross section. The critical temperature of the optimal sample determined with the four-probe method was 103.2 K, and its critical current density values were 0.06 MA cm−2 (77 K, self-field) and 1.91 MA cm−2 (4.2 K, self-field), which were obtained by AC susceptibility measurement and a superconducting quantum interference device, respectively. This study demonstrated the feasibility of fabricating (Bi, Pb)-2223 thin films with superconducting performance via the low-cost CSD method.

Effect of alkali metal Na on the formation and superconductivity of Tl-1212-type phase (Tl0.85Cr0.15)Sr2−xNaxCaCu2O7

The effect of Na substitution on the formation and superconductivity of Tl-1212-type phase (Tl0.85Cr0.15)Sr2−xNaxCaCu2O7 (x = 0–0.30) is reported. The samples were prepared via the solid-state reaction method. X-ray diffraction patterns showed the presence of Tl-1212-type phase or Ca0.3Sr0.7CuO2 (CSCO) as a major or minor phase in the samples. The resistance versus temperature curves showed onset transition temperature, Tc-onset between 97 and 106 K and zero-resistance temperature, Tc-zero between 88 and 99 K. AC susceptibility measurement showed superconducting transition $${T_{{\text{c}}{\chi ^\prime }}}$$ between 89 and 98 K. The peak temperature, Tp, of the imaginary part of the susceptibility, χ″, was the highest for x = 0.02 sample (Tp = 96 K). The inter-grain critical current density, Jc, at Tp for x = 0 sample was Jc (Tp = 68 K) = 14 A cm−2 and for x = 0.02, 0.20 and 0.30 Jc (Tp) at 96, 96, and 88 K, respectively, is 19 A cm−2. Na substitution increased the grain size of the Tl-1212 samples. All Na-substituted samples showed higher transition temperature, enhanced critical current density, and improved inter-grain coupling compared with the non-substituted sample. This work showed that other than rare-earth elements, monovalent alkali metal such as Na could also be used to enhance the superconducting properties of the Tl-1212 phase.

Microwave Signature of Topological Andreev level Crossings in a Bismuth-based Josephson Junction.

Demonstrating the topological protection of Andreev states in Josephson junctions is an experimental challenge. In particular the telltale 4π periodicity expected for the current phase relation has remained elusive, because of fast parity breaking processes. It was predicted that low temperature ac susceptibility measurements could reveal the topological protection of quantum spin Hall edge states by probing their low energy Andreev spectrum at finite frequency. We have performed such a microwave probing of a phase-biased Josephson junction built around a bismuth nanowire, a predicted second order topological insulator, and which was previously shown to host one-dimensional ballistic edge states. We find absorption peaks at the Andreev level crossings, whose temperature and frequency dependencies point to protected topological crossings with an accuracy limited by the electronic temperature of our experiment.

Hexanuclear and Heptanuclear Nickel(II) Complexes of with a Non-Schiff-Base Tetradentate Ligand: an Example of Slow Motion Ferromagnetic Phase Transition at Very Low Temperature

Hexanuclear and heptanuclear nickel(II) complexes with N,N′-bis(2-hydroxy-3,5-dimethylbenzyl-1,2-ethanediamine (H2hdde), [Ni6(hdde)3(OH)4(NO3)2(H2O)2]·2dmf (dmf = N,N-dimethylformamide) and [Ni7(hdde)3(OH)6(dmac)3](ClO4)2 (dmac = N,N-dimethylacetamide), were investigated. The latter complex was newly synthesized and the single-crystal X-ray structure analysis revealed a wheel-shaped heptanuclear cluster. These complexes showed a ferromagnetic interaction in the temperature dependence of magnetic susceptibilities. The micro-SQUID data of the former complex did not show SMM property, whereas the AC susceptibility measurements suggested SMM-like behavior and the zero-field-cooled and field-cooled studies showed a ferromagnetic transition near 240 mK for the latter complex.

A novel characterization technique for superparamagnetic iron oxide nanoparticles: The superparamagnetic quantifier, compared with magnetic particle spectroscopy.

Superparamagnetic iron oxide nanoparticles (SPIONs) are used as a tracer material in sentinel node biopsies. The latter is a procedure to analyze if cancer cells have spread to lymph nodes, helping to personalize patient care. To predict SPION behavior in vivo, it is important to analyze their magnetic properties in biological environments. The superparamagnetic quantifier (SPaQ) is a new device to measure the dynamic magnetization curve of SPIONs. The magnetization curve was measured for two types of SPIONs: Resovist and SHP-25. We used three techniques: Vibrating Sample Magnetometry (VSM), Magnetic Particle Spectroscopy (MPS), and our new SPaQ. Furthermore, AC susceptibility (ACS) measurements were performed as part of the evaluation of the three techniques. SPaQ and VSM results were found to be similar. Measurement results were nearly identical in both directions, indicating minor hysteresis. However, in MPS measurements, a clear hysteresis loop was observed. Furthermore, the ACS measurements showed a pronounced Brownian maximum, indicating an optimal response for an AC frequency below 10 kHz for both particle systems. Both the SPaQ and MPS were found to be superior to VSM since measurements are faster, can be performed at room temperature, and are particularly sensitive to particle dynamics. The main difference between the SPaQ and MPS lies in the excitation sequence. The SPaQ combines an alternating magnetic field that has a low amplitude with a gradual DC offset, whereas MPS uses only an alternating field that has a large amplitude. In conclusion, both the SPaQ and MPS are highly suited to improve understanding SPION behavior, which will lead to the radical improvement of sentinel node biopsy accuracy.

Novel Experimental Approach to Obtain the Oxygen-Deficient LaBaCaCu3Oy Superconductor Compound

This work presents a novel approach based on the nitrate decomposition method for the preparation the oxygen-deficient LaBaCaCu3Oy (La1113) compound. The XRD results reveal the presence of the triple perovskite structure LaBaCaCu3Oy as a dominant phase crystallizing in the tetragonal system with the space group P4/mmm. The SEM observation shows a low porosity and EDAX data indicates the presence of the basic elements of the phase. The superconducting character of the compound is confirmed by AC susceptibility measurements with Tc = 63 K even if the samples are not treated under oxygen atmosphere.

Vortex dynamics behavior with third harmonic ac-susceptibility for nano Fe-doped MgB2 superconductor

In the present study, the nano Fe-doped MgB2 samples with different doping contents (0 wt% ≤ x ≤ 6 wt%) were synthesized by the solid-state reaction technique. The fundamental and third harmonic real and imaginary components of ac-susceptibility were measured with an ac-applied field of Hac = 0.5 Oe under the different frequency range f = 1–3 kHz. The amplitude of the peaks in the first harmonic imaginary component as a function of temperature, $${\chi ^{\prime\prime}_1}(T)$$ plots enhances regularly as we increase the frequency and shifted towards the higher temperature region. The highest amplitude of the peak is shown by 3 wt% doped sample among the undoped and doped sample in $${\chi ^{\prime\prime}_1}(T)$$ plot. The χ3″ reveals the sinusoidal oscillation with maxima and minima of the ratio δ, a parameter associated with the penetration depth of the ac-applied field. The amplitude of the real component χ3′ is smaller than the imaginary component of χ3″ in third harmonic ac-susceptibility measurements. The 6 wt% nano-Fe doped MgB2 sample shows the multiple real and imaginary peaks of third harmonic ac-susceptibility, χ3. The irreversibility line (IL) is shifted towards the higher temperature site with the increases of frequency. The slope of the IL increases with the increase of frequency.

The effect of Ba doping on Sr site on structural and superconducting properties of Bi2212 phase

In this research, we investigate the effect of Ba substitution on Sr sites in the Bi-2212 system. X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray spectrometry (EDS), Raman spectroscopy and AC susceptibility measurements give structural and magnetic properties of the prepared samples. The results reveal the following. X-ray diffraction shows that the Bi-2212 phase is dominant and that the secondary Bi-2201 phase decreases as Ba content increases. Ba doping decreases the cell parameter of the samples. SEM reveals a structure of well-connected grains with a shape of plate. Raman spectroscopy shows the modes of vibration that are present in the superconducting material Bi2Sr(2-x)BaxCaCu2O8+δ. AC susceptibility shows that Ba substitution decreases the critical temperature (Tc).

Mononuclear and trinuclear DyIII SMMs with Schiff-base ligands modified by nitro-groups: first triangular complex with a N-N pathway.

Using two Schiff-base ligands containing an electron-withdrawing group (NO2), we obtained two mononuclear and two trinuclear complexes with the general formula [Dy(hni)(NO3)(DMF)2]·DMF (1·DMF), [Dy(hni)2(H2O)2]·NO3·EtOH (2·NO3·EtOH), [Dy3(hnc)3(DMF)6] (3) and [Gd3(hnc)3(DMF)6] (4) (H-hni: 2-(hydroxyl-3-methoxy-5-nitrophenyl)methylene(isonictino)hydrazine and H3-hnc: 1,5-bis(2-hydroxy-3-methoxy-5-nitrobenzylidene)carbonohydrazide). Four complexes were confirmed by infrared spectroscopy and single-crystal X-ray diffraction. The crystal structure of complex 3 reveals that the modified Schiff-base ligand provides two different tridentate coordination pockets (ONN and ONO) to encapsulate DyIII with a unique N-N pathway. The magnetic properties of all four complexes have been investigated using dc and ac susceptibility measurements. The frequency-dependent ac susceptibility is indicative of single-molecule magnetic behavior without and/or with an optimum dc field with a relaxation barrier Ueff = 34 K (400 Oe), 19 K (0 Oe) and 80 K (0 Oe) for complexes 1, 2 and 3, respectively.

Pressure-induced new spin-states in Ni-25at%Mn mechanical alloy under high pressure

AC-susceptibility measurements in mechanically alloyed Ni-25at%Mn were made under high hydrostatic pressures up to 7.5 GPa by using a cubic anvil press in the low-temperature range from 4.2 K to 300 K. At ambient pressure a reentrant spin glass (RSG) state was observed below 58 K, followed by a ferromagnetic (FM) state with the Curie temperature (TC) at 120 K. Tc decreased with increasing pressure up to 4.3 GPa, while the transition temperature from RSG to FM increased to merge with Tc at 70 K, and then, with further increasing pressure the FM state disappeared, and a spin glass (SG) state appeared. The local moments of this high-pressure SG phase decreased with pressure. The results were compared with a bulk alloy made by the conventional method of melting. In the bulk alloy, a new high-pressure magnetic phase appeared having almost pressure-independent local magnetic moments.

Field-induced slow magnetic relaxation in two-dimensional and three-dimensional Co(ii) coordination polymers.

Two coordination polymers formulated as [Co(1,4-bimb)0.5(5-aip)(H2O)]n (1) and [Co(1,4-bib)1.5(5-hip)(H2O)]n (2) (1,4-bimb = 1,4-bis(imidazol-1-ylmethyl)benzene, 5-aip = 5-aminoisophthalic acid, 1,4-bib = 1,4-bis(1-imidazolyl)benzene and 5-hip = 5-hydroxyisophthalic acid) have been prepared and structurally characterized. Complex 1 is a two-dimensional (2D) network where Co(ii) is six coordinate in a CoO4N2 coordination environment, while the structure of 2 consists of a three-dimensional (3D) framework built from mononuclear Co(ii) units with distorted octahedral geometry as nodes. Static magnetic studies show that first-order orbital angular momentum may play an important role in the magnetic properties of 1, whereas strong easy-axis anisotropy (D = -102 cm-1) was observed in 2. Alternating current (ac) susceptibility measurements demonstrate that both the complexes display field-induced single ion magnet (SIM) behavior.

Slow magnetization dynamics in a six-coordinate Fe(ii)-radical complex.

A new paramagnetic ligand, betaDTDA, and its coordination complex with Fe(hfac)2 are reported (betaDTDA = 4-(benzothiazol-2'-yl)-1,2,3,5-dithiadiazolyl; hfac = 1,1,1,5,5,5-hexafluoroacetylacetonato-). The neutral radical betaDTDA is the first dithiadiazolyl ligand designed to include an electropositive sulphur moiety outside the thiazyl heterocycle, increasing the capacity for supramolecular, structure-directing electrostatic contacts and enabling new pathways for magnetic exchange. The Fe(hfac)2(betaDTDA) complex is composed of a hs-Fe(ii) center with the three bidentate ligands arranged about the ion in a distorted octahedral 6-coordinate environment. The magnetic properties of crystalline Fe(hfac)2(betaDTDA) are consistent with strong antiferromagnetic (AF) coupling between the metal and ligand moments, giving rise to a well-defined Stotal = 3/2 ground state that is the only thermally populated state below 40 K. Below 4 K, this complex exhibits slow relaxation of the magnetization detected by ac susceptibility measurements consistent with a single-molecule magnet (SMM) behaviour.

New Cobalt(II) Field‐Induced Single‐Molecule Magnet and the First Example of a Cobalt(III) Complex with Tridentate Binding of a Deprotonated 4‐Amino‐3,5‐bis(pyridin‐2‐yl)‐1,2,4‐Triazole Ligand

From Co(NO3)2·6H2O ‐ NaN3 ‐ abpt reaction system, a mononuclear complex [Co(abpt)2(N3)2] (abpt = 4‐amino‐3,5‐bis(pyridin‐2‐yl)‐1,2,4‐triazole) (1) and a dinuclear complex [Co2(abpt)(µ‐abpt‐H)2(N3)4]·1.12H2O (2) were obtained. The presence of neutral abpt, as well as azido ligands was proved by IR spectroscopy. X‐ray crystallography shows that 1 is a molecular CoII complex with two azido ligands coordinated in trans‐positions, while 2 is a dinuclear CoIII complex bridged by two abpt‐H ligands. π–π stacking interactions between pyridyl rings of abpt and N‐H···N and C‐H···N hydrogen bonds in 1 and 2 stabilize their structures by creating a 3D supramolecular network. The analysis of the magnetic properties of 1 revealed negative zero‐field splitting parameter D = –24.1 cm–1 supported also by CASSCF/NEVPT2 and CASSCF/CASPT2 theoretical calculations. The X‐band electron paramagnetic resonance also gives an evidence for a strong rhombic character of the anisotropy. The investigation of the ac susceptibility measurements identified 1 as a field‐induced single‐molecule magnet, in which direct, Raman and Orbach relaxation processes are present.

Magnetic properties of disordered interacting electron system FeAl2-xGax (0 ≤ x ≤ 0.5): Origin of local moment behaviour and the stabilization of an antiferromagnetic phase by weak interplanar magnetic interaction

In this report, we have investigated the magnetic properties of the disordered interacting electron system FeAl2-xGax (0 ≤ x ≤ 0.5) through the measurements of dc magnetization, ac susceptibility and heat capacity, and constructed the magnetic phase diagram. This system shows an intriguing phenomenon in which an antiferromagnetic transition occurs concomitantly with a disorder-induced weak localization of electrons implying a cooperative nature of the disorder-induced effects and electron-electron interactions which is in contradiction to their established competitive nature. Our investigation reveals that, in addition to the antiferromagnetic transition at TN, a spin glass transition occurs at a lower temperature at Tg (Tg < TN). As the Ga concentration increases, TN increases while Tg decreases. The investigation reveals that the Fe-Fe antiferromagnetic interactions predominantly lie in a plane and the antiferromagnetic phase is stabilized by a weak interplanar Fe-Fe interaction. With increasing Ga concentration, this interplanar Fe-Fe distance decreases and results in the increase of the Néel temperature TN. Fe moments in this system are found to be partially localized due to the interplay between disorder and electron-electron interactions. Competing interactions between the finite spin clusters give rise to a cluster spin glass state at low temperatures.

Synthesis, Crystal Structures, and Magnetic Properties of New Hexanuclear MnIII2LnIII4 Complexes: SMM Behavior of the Terbium(III) Analogue

This investigation reports the syntheses, crystal structures, and magnetic properties of a series of isomorphous hexanuclear MnIII2LnIII4 compounds of composition [MnIII2LnIII4L12L22(µ3‐OH)4(µ1,3‐Pivalate)6(NO3)2]·2CH3CN {Ln = Tb (1), Dy (2), Ho (3), Er (4)}, where H2L1 is the Schiff base ligand that is obtained by [1+1] condensation of 3‐methoxysalicylaldehyde (HL2) with 2‐amino‐2‐methyl‐1‐propanol. While the O(phenoxo)N(imine)O(alkoxo) pocket of the ligand [L1]2– binds a MnIII ion, the other pocket, O(methoxy)O(phenoxo), remains noncoordinated. In contrast, each of the O(methoxy)O(phenoxo) and O(phenoxo)O(aldehyde) sites of [L2]– is occupied by a LnIII ion. Additionally, there are four µ3‐hydroxo, six µ1,3‐pivalate, and two chelating nitrate ligands, stabilizing the hexanuclear cores. Magnetic susceptibility (2–300 K) and magnetization (M) data reveal significant anisotropy in 1–4. Detailed ac susceptibility measurements have revealed single molecule magnet (SMM) behavior in the TbIII analogue with Ueff = 11.12 cm–1 and τ0 = 1.04 × 10–7 s under a 1000 Oe dc field and Ueff = 10.42 cm–1 and τ0 = 1.62 × 10–7 s under a 3500 Oe dc field, while the other three analogues do not show slow relaxation of magnetization.

AC susceptibility and electrical properties of rare-earth- and alkali metal-substituted (Tl0.7M0.3)Sr2CaCu2O7 with M = Er, Gd, La, Na, K and Rb

The effects of rare-earth elements M = Er, Gd and La, and alkali metals M = Na, K and Rb substitution on (Tl0.7M0.3)Sr2CaCu2O7 (Tl-1212) are reported. The rare-earth elements were chosen by considering the ionic radius, i.e., from the smallest (Er+3) to the largest (La+3) ion. The samples were prepared via the solid-state reaction method. X-ray diffraction patterns showed the presence of major Tl-1212 and minor Tl-1201 and Ca0.3Sr0.7CuO2 phase in almost all samples. The resistance versus temperature curves for the rare-earth-substituted samples showed onset temperature between 87 and 90 K and zero resistance temperature between 69 and 81 K. Alkali metal substitutions exhibited Tl-1212 phase but showed no superconducting transition although the electrical resistivity was much lower than the rare-earth-substituted samples. AC susceptibility measurement showed superconducting transition Tcχ, between 59 and 80 K for the rare-earth element-substituted samples. The average grain size, the transition temperature, Tcχ and the peak temperature Tp of the imaginary part of the susceptibility χ″ decreased as the ionic radius of the rare earths was reduced.

Investigation of the structural, magnetic and electrical properties of the Au doped YBCO superconductors

In this study, a systematic investigation of Au-added YBa2Cu3O7−x (YBCO) samples has been undertaken mainly to understand their structural, magnetic as well as electrical behavior. In order to get high quality of superconducting bulk samples, optimum preparation conditions have been provided. The bulk samples were produced by conventional solid state reaction method at 930 °C under the low oxygen atmosphere. The bulk samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), electron dispersive X-ray, dc electrical resistivity (ρ-T), critical current density and ac magnetic susceptibility measurements. The samples were carried out by means of powder X-ray diffraction for phase analyses, and lattice parameters, SEM for microstructure examinations. From XRD and SEM results, an increase in the intensity of main peaks and average grain size but a increase in the lattice parameter c with addition of Au in comparison with the unadded sample. In addition to this, onset-offset critical transition temperature ( $${T}_{c}^{on}, {T}_{c}^{off}$$ ) was determined from dc electrical resistivity ( $$\rho -T$$ ) as a function of temperature measurements. Moreover, the transition temperature (Tc) and the critical current density (Jc) are enhanced upon Au addition when compared with unadded YBCO superconductor sample. The increment of Au content decreased the transition temperature and the critical current density values. From the AC susceptibility measurements, inter-grain, intra-grain peak temperature and superconducting transition temperature were determined. The possible reasons for the observed improvements in structural, magnetic and electrical properties due to the Au addition in the YBCO samples were discussed by comparison with other studies about addition of transition metals in high temperature superconductors.

Impact of Ag-Doped on the Ferromagnetic-Metallic Transition in Pr0.75Na0.25mno3 Manganites

Monovalent doped Pr0.75Na0.25-yAgyMnO3 (y = 0–0.10) manganite have been investigated using X-ray diffraction (XRD) and scanning electron microscope (SEM) as well as DC electrical resistivity and AC susceptibility measurement to clarify the influence of Ag- doped on charge ordering (CO) state. XRD analysis revealed all samples consists of essentially single phase and crystallized in an orthorhombic structure with space group Pnma. SEM images of Pr0.75Na0.25-yAgyMnO3 compound shows the successful substitution of Ag+ ions with the enhancement of the grains boundaries and sizes as well as the compaction of particles. On the other hand, resistivity and susceptibility measurements showed that the y = 0 sample exhibits insulating behavior and anti-ferromagnetic. Interestingly, the ferromagnetic-metallic transition was observed for y = 0.05 due to the revival of double-exchange (DE) mechanism as a result of weakening the Jahn-Teller effect which caused the CO state to be weakened. However, increasing of Ag-doped up to y = 0.10 induce back its transition into anti-ferromagnetic insulating behavior suggestively due to the weakening of DE mechanism.

Spin-glass behavior in KxRu4−yNiyO8 hollandite materials

We report the synthesis and comprehensive ac and dc susceptibility measurements of ${\mathrm{K}}_{x}\mathrm{R}{\mathrm{u}}_{4\ensuremath{-}y}\mathrm{N}{\mathrm{i}}_{y}{\mathrm{O}}_{8}$ hollandite. The value of the relative frequency shift, $\ensuremath{\delta}{T}_{f}$, has been determined as 0.025 which is within the range expected for spin-glass systems (0.005--0.06). Additionally, the characteristic flipping time of a single spin flip, ${\ensuremath{\tau}}_{0}$, and the dynamical critical exponent, $\ensuremath{-}zv$, were determined to have values of $5.82\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}\phantom{\rule{0.16em}{0ex}}\mathrm{s}$ and 6.1(3), respectively from the power law. While the value of ${\ensuremath{\tau}}_{0}$ is comparatively very large, $\ensuremath{-}zv$ is consistent with what is expected for spin-glass systems. Field-cooled hysteresis behavior demonstrates a small increase in the remnant magnetization (at 2 K) on increasing the strength of the cooling field, suggesting that the degree of short-range correlations increases consistent with the formation of larger spin clusters. Thermoremnant magnetization data indicate an exponential-like decay of the magnetization as a function of time with the remnant magnetization remaining nonzero. However, it is clear from these data that multiple components contribute to the decay behavior. Collectively, these data confirm spin-glass character for ${\mathrm{K}}_{0.73(3)}\mathrm{N}{\mathrm{i}}_{1.9(5)}\mathrm{R}{\mathrm{u}}_{2.1(5)}{\mathrm{O}}_{8}$ and clearly demonstrate that the magnetic behavior of this material is far from simplistic.

Anisotropic re-entrant spin-glass features in a metallic kagome lattice, Tb3Ru4Al12

We present the results of ac and dc magnetic susceptibility and isothermal magnetization measurements (T = 2–300 K) on the single crystals of a metallic kagome lattice, Tb3Ru4Al12, reported recently to undergo reentrant magnetism with the onset of long range antiferromagnetic order below (TN =) 22 K. The magnetization data obtained on the crystal with the c-axis orientation along magnetic-field reveal spin-glass-like characteristics near 17 K (below TN). However, for the orientation along basal plane, such glassy anomalies are not observable above 2 K. In this respect, this compound behaves like an ‘anisotropic’ re-entrant spin-glass. Possible implications of this finding to the field of 'geometrically frustrated magnetism' are considered.