Lock-in Temperature Research Articles

Microstructure and Superconducting Properties of Bi-2223 Synthesized via Co-Precipitation Method: Effects of Graphene Nanoparticle Addition.

The effects of graphene addition on the phase formation and superconducting properties of (Bi1.6Pb0.4)Sr2Ca2Cu3O10 (Bi-2223) ceramics synthesized using the co-precipitation method were systematically investigated. Series samples of Bi-2223 were added with different weight percentages (x = 0.0, 0.3, 0.5 and 1.0 wt.%) of graphene nanoparticles. The samples' phase formations and crystal structures were characterized via X-ray diffraction (XRD), while the superconducting critical temperatures, Tc, were investigated using alternating current susceptibility (ACS). The XRD showed that a high-Tc phase, Bi-2223, and a small low-Tc phase, Bi-2212, dominated the samples. The volume fraction of the Bi-2223 phase increased for the sample with x = 0.3 wt.% and 0.5 wt.% of graphene and slightly reduced at x = 1.0 wt.%. The ACS showed that the onset critical temperature, Tc-onset, phase lock-in temperature, Tcj, and coupling peak temperature, TP, decreased when graphene was added to the samples. The susceptibility-temperature (χ'-T) and (χ″-T) curves of each sample, where χ' and χ″ are the real and imaginary parts of the susceptibility, respectively, were obtained. The critical temperature of the pure sample was also measured.

Quadrupole modelling of dual lock-in method for the simultaneous measurements of thermal diffusivity and thermal effusivity

The simultaneous measurement of thermal diffusivity and thermal effusivity based on the temperature wave analysis (TWA) is proposed by introducing the dual lock-in temperature sensor with a photo-thermal ac heat source. The thermal effect from each component in the multilayered experimental system is simulated by the quadrupole modeling adopted to the pure periodic heating of the temperature wave. The frequency dependency of the thermal effect from the thermal contact resistance and capacitance in the sensor were analyzed and minimized by taking the optimal frequency range of the temperature wave. The proposed method is applied to examine the nematic-isotropic phase transition of the liquid crystal 4′-(pentyloxy)-4-biphenyl carbonitrile (5OCB). The results were compared with the previous results measured with a single sensor and the advantage of the dual lock-in temperature sensor was demonstrated.

Comparative Study on AC Susceptibility of YBa2Cu3O7−δ Added with BaZrO3 Nanoparticles Prepared via Solid-State and Co-Precipitation Method

Polycrystalline samples of YBa2Cu3O7−δ (Y-123) added with x mol% of BaZrO3 (BZO) nanoparticles (x = 0.0, 2.0, 5.0, and 7.0) were synthesized using co-precipitation (COP) and solid-state (SS) method. X-ray diffraction (XRD) patterns showed the formation of Y-123 and Y-211 as the major and minor phases, respectively. The samples prepared using COP method showed higher weight percentage of Y-123 phase (≤98%) compared to the SS samples (≤93%). A peak corresponding to BZO was also found in the samples added with BZO nanoparticles. The increasing intensity of the BZO peak as the BZO amount increased showed the increasing amount of the unreacted nanoparticles in the samples. Refinement of unit cell lattice parameters indicated that all the samples have an orthorhombic crystal structure and there is no orthorhombic-tetragonal phase transformation. As observed using scanning electron microscopy (SEM), all the samples showed randomly distributed grains with irregular shape. The average grain size for the pure sample prepared using COP method is smaller (0.30 µm) compared with that of the pure SS sample (1.24 µm). Addition of 7.0 mol% BZO led to an increase of average grain size to 0.50 μm and 2.71 μm for the COP and SS samples, respectively, indicating grain growth. AC susceptibility (ACS) measurement showed a decrease in the onset critical temperature, Tc-onset with BZO addition. Comparatively, Tc-onset for the COP samples is higher than that of the SS samples. The value of Josephson’s current, Io increased up to 2.0 mol% BZO addition, above which the Io decreased more drastically for the SS samples. The value of Io is 53.95 μA and 32.08 μA for the 2.0 mol% BZO added SS and COP samples, respectively. The decrease of Io is attributed to the distribution of BZO particles at the grain boundaries as also reflected in the drastic decrease of phase lock-in temperature, Tcj. As a result of smaller average grain size, the presence of more grain boundaries containing insulating BZO particles led to lower Io in the COP samples.

Effects of charge-density-wave phase transition on electrical transport and Raman spectra in 2H-tantalum disulfide

Measurements of electrical transport and Raman spectroscopy are performed on 2H-TaS2 to study the formation and the character of the charge density wave. The entry of the charge-density-wave state below the lock-in temperature is detected by the sudden change of the resistivity slope with temperature, the sharp rise of the magneto-resistivity, and the significant change in the Hall coefficient. Meanwhile, the frequency of the two-phonon mode decreases with decreasing temperature. When approaching the lock-in temperature, the formation of the charge density wave is also evidenced by the disappearance of the two-phonon mode. In the charge density wave state, the newly born charge-density-wave modes in the E2g- and A1g-symmetries exhibit a blue-shift with decreasing temperature. These results suggest that the combined techniques of electrical transport measurement and Raman spectroscopy are powerful in studying the charge-density-wave order in materials with strong electron-phonon coupling.

Studies of magnetic phase transitions in orthorhombic DyMnO3 ceramics prepared by acrylamide polymer gel template method

Abstract Single phase polycrystalline DyMnO3 (DMO) was synthesized using acrylamide polymer gel template method. We report the structural, magnetic, specific heat and dielectric properties of DMO over wide experimental conditions. Room temperature XRD pattern shows the formation of singe phase material without any impurity. The magnetic properties such as magnetization versus temperature (M vs. T) and magnetization versus magnetic field (M vs. H) were studied around the transition temperatures region. The temperature dependent magnetization data suggest two phase transitions corresponding to the lock-in temperature below which ferroelectric ordering exist (around 19 K; Tlock) and antiferromagnetic (AFM) ordering of Dy spin (around 8 K; TN (Dy)). The magnetic hysteresis obtained were fitted to extract weak ferromagnetic (FM) and antiferromagnetic/paramagnetic (AFM/PM) contribution to the magnetic data. The order of magnetic transitions were analyzed from Arrott plot. The temperature dependent specific heat measurement shows all three phase transitions corresponding to (i) AFM ordering of Mn spin (around 38 K; TN(Mn)), (ii) Tlock transition and (iii) TN(Dy) transition. The effect of magnetic field to the transitions were studied using specific heat capacity measurement. The peak intensity of TN(Dy) decreases on the application of magnetic field whereas peak intensity of Tlock increases with increase in magnetic field in specific heat measurement. Further the third anomaly, TN (Mn) remains more or less unaffected by the application of magnetic field. The intrinsic dielectric behaviour of the material was observed up to 160 K, above this temperature there is large increase in dielectric value due to the contribution from Maxwell- Wagner polarization.

AC Susceptibility of BaZrO3 Nanoparticles Added YBa2Cu3O7−δ Superconductor Prepared via Coprecipitation Method

In this work, magnetic properties of polycrystalline samples YBa2Cu3O7−δ added with x mol.% of BaZrO3 (BZO) nanoparticles (x = 0.0, 1.0, 2.0, 3.0, 5.0, and 7.0) were studied by AC susceptibility (ACS) measurement. The samples were prepared using coprecipitation (COP) method. X-ray diffraction (XRD) results showed that all the samples were composed of Y-123 as the major phase and Y-211 as the secondary phase. XRD peak of BZO was also observed in the samples added with BZO nanoparticles. The intensity of the peak became higher with increasing amount of BZO addition indicating the presence of increased amount of the unreacted nanoparticles in the samples. The refined lattice parameters indicated that all the samples have an orthorhombic crystal structure without the occurrence of orthorhombic-tetragonal phase transformation. Scanning electron microscopy (SEM) images showed that the samples have randomly distributed grains with irregular shape. The average grain size increased from 0.30 μ m for the pure sample to 0.50 μ m for the BZO addition of 7.0 mol.%. ACS measurement showed a slight decrease of onset critical temperature, Tc−onset (< 1 K) with BZO addition. Both phase lock-in temperature, Tcj, and coupling peak temperature, Tp, remained relatively unchanged for BZO addition up to 3.0 mol.%. Based on the Bean critical state model, the calculated intergranular critical current density, Jcm, for the pure sample is 1.88 A/cm2 at Tp = 84.8 K. For the sample added with 7.0 mol.% of BZO, Jcm at Tp = 83.6 K is 1.95 A/cm2.

Metastable states and defect density waves in modulated ferroelectrics

ABSTRACTThe influence of defects on the phase behaviour of Rb-doped K2ZnCl4-single crystals is studied using high-resolution gamma-ray diffractions in combination with in situ dielectric impedance spectroscopy. It is shown that the interaction between strain fields near discommensurations within the incommensurate phase and impurity ions lead to the formation of defect density waves. On rapid cooling, these are unable to relax and persist within the commensurate phase thus acting as an intrinsic memory. Hence, a metastable re-entrant incommensurate phase is observed on heating at temperatures well below the normal lock-in temperature that is found in equilibrium studies.

Cation distribution dependent magnetic properties in CoCr2-xFexO4 (x = 0.1 to 0.5): EXAFS, Mössbauer and magnetic measurements.

In this report, we have examined the evolution of the structure and rich magnetic transitions such as a paramagnetic to ferrimagnetic phase transition at the Curie temperature (TC), spiral ordering temperature (TS) and lock-in temperature (TL) observed in the CoCr2O4 spinel multiferroic after substituting Fe. The crystal structure, microstructure and cation distribution among the tetrahedral (A) and octahedral (B) sites in the spinel lattice are characterised by X-ray diffraction, transmission electron microscopy, Extended X-ray Absorption Fine Structure (EXAFS) and Mössbauer spectroscopy. Due to the same radial distances of the first coordination shell in both tetrahedral and octahedral environments observed in EXAFS spectra, the position of the second coordination shell specifies the preference of more Fe ions towards the A site at x = 0.1. At x = 0.5, more Fe ions favour the B site. The cation distribution quantitatively obtained from the Mössbauer spectral analysis shows that while 60% of Fe ions occupy the A site in x = 0.1, 40% occupy it in x = 0.5. Surprisingly at x = 0.3, Fe ions are distributed equally among the A and B sites. dc magnetization reveals an increase in TC from 102 K to 200 K and in TS from 26 to 40 K with an increase in Fe concentration, indicating an enhancement in A-B exchange interaction at the expense of B-B. No report has until now demonstrated such an enhancement in TS either in pure or in doped CoCr2O4. Furthermore, frequency-dependent ac susceptibility (χ) data fitted with different phenomenological models such as the Néel-Arrhenius, Vogel-Fulcher and power law confirm a spin-glass and/or cluster-glass behaviour in nanoparticles of CoCr2-xFexO4.

Surface-Temperature Measurement and Submicron Defect Isolation for Microelectronic Devices Using Thermoreflectance Microscopy

Thermal analysis of small defects becomes essential for understanding the influence of hotspots, which affect the device performance, such as the operating speed and reliability. In this paper, we demonstrate a CCD-based thermoreflectance microscopy (TRM) system as a noncontact thermal analysis technique especially for submicron defects on microelectronic devices. By employing a lock-in detection technique and temperature calibration process, the surface temperature distribution of a polysilicon microresistor and submicron defects that are not distinguishable in conventional optical microscope images can be quantitatively measured with high thermal (up to \(\sim \)13 mK) and spatial (\(\sim \)670 nm) resolution. In addition, the accuracy of quantitative temperature measurement and small defect isolation by the TRM system is compared with that obtained from an infrared thermography (IRT) system.

Observation of anomalous phonons in orthorhombic rare-earth manganites

We observe the appearance of a phonon near the lock-in temperature in orthorhombic REMnO3 (RE denotes rare earth) (RE: Lu and Ho) and anomalous phonon hardening in orthorhombic LuMnO3. The anomalous phonon occurs at the onset of spontaneous polarization. No such changes were found in incommensurate orthorhombic DyMnO3. These observations directly reveal different electric polarization mechanisms in the E-type and incommensurate-type orthorhombic REMnO3.

Magnetodielectric coupling in MnCr 2O 4 spinel

We have investigated the magnetic and dielectric properties of polycrystalline samples of the spinel MnCr 2O 4. Below the ferrimagnetic ordering temperature at T N∼43 K, both magnetization and dielectric measurements show signatures of the onset of a conical structure at T s∼17 K and a lock-in temperature at T f∼14 K. These values are similar to those previously reported for single-crystal samples, where the spiral structure is short-range ordered (SRO) at low temperatures. The application of magnetic field suppresses the dielectric anomaly at T f indicating that the coherence length of the ordering increases. MnCr 2O 4 exhibits a symmetrical magnetodielectric response between T f and T s that scales with the square of the magnetization. This suggests that the magnetodielectric coupling originates from the P 2 M 2 term in the free energy expansion. The magnetodielectric response becomes asymmetric with respect to field below T f.

A heterodyne method for the thermal observation of the electrical behavior of high-frequency integrated circuits

The observation of spectral components of the power dissipated by devices and circuits in integrated circuits (IC) by temperature measurements is limited by the bandwidth of either the temperature transducer or the intrinsic cut-off frequency provided by the thermal coupling inside the chip. In this paper, we use a heterodyne method to observe the high-frequency behavior of circuits and devices by means of low-frequency lock-in temperature measurements. As experimental results, two applications of the technique are presented: detection of hot spots in ICs activated by high-frequency electrical signals and the observation of the frequency response of an integrated resistor through temperature measurements. The heterodyne method has been used in this paper with four different measurement techniques: embedded differential BiCMOS temperature sensor, laser reflectometer, laser interferometer and internal IR laser deflection meter.

Short-range magnetic interactions in the spin-ice compoundHo2Ti2O7

Magnetization and susceptibility studies on single crystals of the pyrochlore Ho$_{2}$Ti$_{2}$O$_{7}$ are reported for the first time. Magnetization isotherms are shown to be qualitatively similar to that predicted by the nearest neighbor spin-ice model. Below the lock-in temperature, $T^{\ast }\simeq 1.97$ K, magnetization is consistent with the locking of spins along [111] directions in a specific two-spins-in, two-spins-out arrangement. Below $T^{\ast}$ the magnetization for $B||[111]$ displays a two step behavior signalling the breaking of the ice rules.

The absence of a discommensuration lattice in the incommensurate phase of

X-ray scattering close to the lock-in temperature has been measured as a function of temperature to investigate whether the discommensuration lattice is a useful description of the structure of . We review different models for the incommensurate structure and discuss how they might be distinguished by a scattering experiment. Our results are compared with earlier published x-ray measurements and with those obtained from nuclear spin-resonance techniques. All of the x-ray results suggest that higher harmonics of the scattering measured in the and planes are much weaker than predicted by the abrupt-discommensuration model. We conclude from the measurements that this theory does not provide an adequate description of the experimental results close to the lock-in transition.

Kinetics of the lock-in phase transition in Rb2ZnCl4

High-resolution X-ray scattering experiments have been performed on single crystals of the incommensurate system Rb2ZnCl4 with emphasis on the kinetics of the lock-in phase transition. The nearly perfect single crystal (mosaic spread approximately=0.6 min) displayed a large hysteresis of 20 K. As the sample was cooled quickly from the paraelectric phase into the commensurate phase, via the incommensurate phase, the time evolution of the disappearance of the incommensurate peak intensity was monitored. The time becomes longer when the sample is quenched to lower than the lock-in temperature, which is contrary to the expected kinetic behaviour of nucleation and growth. The characteristic time of decay exhibits an Arrhenius-like behaviour with an energetic barrier Eb to overcome of the order of 0.37 eV. The origin of the energetic barrier is interpreted in terms of an order-disorder process of the ZnCl4 tetrahedra network.

SHG-investigations of incommensurate A2BX4-crystals

Abstract The complete tensor of nonlinear optical susceptibilities of Rb2ZnCl4 including the relative signs of its components has been measured in the ferroelectric commensurate phases between 15 K and the lock-in temperature using second harmonic generation (SHG). In contrast to published data the susceptibilities turn out to be not proportional to the spontaneous polarization below 140 K. Due to the change to monoclinic symmetry new coefficients appear in the ferroelectric low-temperature phase, which are two orders of magnitude smaller than those of the orthorhombic phase. The decomposition of the tensor of nonlinear susceptibilities into irreducible parts reveals that the proportionality holds between spontaneous polarization and the vector invariants. The temperature dependence of the septor parts of the tensor resembles that of the coefficients.

Influence of crystal synthesis on the incommensurate phase and lock-in transition of Rb2ZnCl4 crystals

Abstract A comparative study of several crystals of Rb2ZnCl4, obtained by different crystal growing methods, has allowed us to determine the influence of growth defects on the incommensurate phase and on the lock-in transition of these samples. X-ray diffraction has allowed us to complete previous dielectric measurements realized on the same samples and to relate the crystalline quality to the evolution of the modulation as a function of the temperature. The principal influence of an increasing defect density seems to be a stronger pinning of the modulated phase and this induces a lower lock-in temperature and a wider hysteresis.

Microstructure of the 'discommensurate' state in NbTe4

A model for the 'discommensurate' structure of NbTe4 is proposed based on the analysis of electron diffraction patterns. It is found that above the lock-in temperature, which is around 50K, the structure can be described either as deformation-modulated or as interface-modulated. Both approaches lead to the same model, which is moreover in agreement with the incommensurate structure determination by Van Smaalen and co-workers (1986). Satellite dark-field and high-resolution electron microscopy both combined with optical diffraction are used to confirm the proposed model.

Theoretical investigation of the antiferromagnet EuAs 3

Semimetallic EuAs 3 is a new incommensurate (IC) antiferromagnet with T N=11.3 K and a lock-in temperature T L=10.26 K to a commensurate (C) phase. Using a realistic exchange model the possible phases are discussed and an IC-phase with the proper modulation is found. The mechanism for the C-lock-in transition is also discussed.

Some properties of thiourea in the single plane wave approximation

Abstract The properties of the incommensurate phase of a linear crystal are obtained, in the SPW approximation, assuming a Gibbs energy density The results are extended to thiourea. The constants in the φ expression are obtained from the dielectric constant ϵx in the paraelectric phase, the spontaneous deformation in the ferroelectric phase, the value of θinc and three properties at θinc: value of the modulation wave vector, variation of θinc with pressure and discontinuity of the static elastic constant c33. In good agreement with the experimental results, we find the lock-in temperature θc (172.2 K), the spontaneous deformation in the incommensurate phase, the variation with temperature of the c33 static value and the Brillouin scattering phenomena around θinc. The variation of the modulation wave vector with temperature is only qualitatively described. The difference between dθinc/dt and dθc/dt may be explained by the dependence on pressure of the constants in the φ function. The agreement between the ...