Harmonic Of Ac Susceptibility Research Articles

Investigation of fundamental and higher harmonic AC magnetic susceptibility of FeSe0.5Te0.5 superconductor

We present the complex harmonic magnetic susceptibilities χn = χ′n-iχ″n (n = 1, 3) of FeSe0.5Te0.5 polycrystalline superconducting sample. The ac magnetic susceptibility is measured as a function of various external perturbations such as temperature T, the ac magnetic field amplitude Hac, frequency υ, and the magnitude of dc bias field Hdc. The in-phase (χ′n) and out of phase (χ″n) components of the fundamental and third harmonics of ac susceptibility are found to vary as a function of ac driven field. Particularly, the curves shift toward lower temperatures with increasing Hac. Contrary to ac magnetic field (Hac), no noticeable change has been observed within the range of applied dc magnetic field (Hdc) of up to 20 Oe. At a fixed ac magnetic field of Hac = 0.5 Oe, both parts of the third harmonics show frequency dependence. The imaginary part of the third harmonics, χ″3 shows a small peak followed by a negative minimum at lower temperatures. The small peak diminishes as the frequency increases. The negative minimum suppresses and shifts towards the higher temperatures as we increase the frequency. To better understand the ac magnetic response under the influence of various perturbations, we have analyzed the polar plots (Cole-Cole) of the complex ac susceptibility for both the harmonics. Our analysis suggests that the studied sample is in a vortex glass state, characterized by a collective flux creep within Bean’s model, while the Kim–Anderson model is ruled out.

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.

Comparison of ${J_{{C}}}$ in GdBCO Tape Using Dc Magnetization and Harmonic Ac Susceptibility Measurements

We have measured the critical current density ( ${J_{{C}}}$ ) of a sample of SuNAM HTS tape using ac susceptibility (ACS) and dc magnetization (DCM) techniques. In DCM measurements, inhomogeneity ( $\delta B$ ) in the applied dc field causes a systematic underestimate of ${J_{{C}}}$ . The error in DCM measurements is characterized by the penetration parameter, $\gamma = \frac{{3\pi {\chi _0}\delta B}}{{({3w - \frac{{{w^2}}}{l}}){\mu _0}{J_{{C}}}}}$ , and grows as ${J_{{C}}}$ decreases. Using a harmonic ACS analysis, we have obtained more accurate measurements of ${J_{{C}}}$ as a function of applied dc field and temperature for $\gamma \approx 1$ .

Crossover from paramagnetic to diamagnetic ac-susceptibility in Bi2Sr2CaCu2O superconductor for

Ac-susceptibility measurements of the superconducting Bi2Sr2CaCu2O single crystal for -axis are presented. In low frequency measurements the first harmonic ac-susceptibility, , is real and independent of the amplitude of the ac-magnetic field (linear behavior) and positive, implying that it represents the slope of the magnetization curve as the temperature changes below Tc2. The positive ac-susceptibility before becoming negative, at low temperatures, forms a positive local maximum arising from the melting transition of the Abrikosov vortex lattice. For higher frequencies the response becomes diamagnetic due to the eddy currents. The signature of the discontinuous change of the magnetization, at the melting transition in higher frequency measurements, is a sharp shoulder near the complete screening. The presence of second harmonic susceptibility in the liquid regime implies nonlinear variation of the equilibrium magnetization.

Defective iron-oxide nanoparticles synthesised by high temperature plasma processing: a magnetic characterisation versus temperature

Magnetic properties and phase compositions of iron-oxide nanoparticles synthesised by a high temperature arc plasma route have been investigated by Mössbauer spectroscopy and high harmonic magnetic AC susceptibility measurements, and correlated with morphological and structural properties for different synthesis conditions. The Mössbauer spectra precisely determined the presence of different iron-oxide fractions in the investigated nanoparticles, while the high harmonic magnetic susceptibility measurements revealed the occurrence of metastable magnetic phases evolving in temperature and time. This study illustrates magnetic properties and dynamics of the magnetic configurations of iron-oxide nanoparticles grown by high temperature plasma, a process less explored so far but extremely useful for synthesising large numbers of nanoparticles for industrial applications.

The spin glass behavior in the Heusler alloy Cu2VAl

The magnetic properties of the Heulser alloy Cu2VAl were comprehensively investigated. A broad maximum at low temperature in both zero-field-cooled magnetization and the real part of the linear ac susceptibilities as well as a clear irreversibility between the zero-field-cooled and field-cooled magnetization curves were detected. The absence of the second harmonic ac susceptibility and a negative peak observed in the third harmonic ac susceptibility indicate its spin glass ground state. Fitting of the temperature dependences of the linear ac susceptibilities with different frequencies to the Vogel–Fulcher model and the critical slowing down power law confirms the spin glass nature of the detected magnetic behavior at low temperature in the Heusler alloy Cu2VAl.

Correspondence between neutron depolarization and higher order magnetic susceptibility to investigate ferromagnetic clusters in phase separated systems

It is a tough task to distinguish a short-range ferromagnetically correlated cluster-glass phase from a canonical spin-glass-like phase in many magnetic oxide systems using conventional magnetometry measurements. As a case study, we investigate the magnetic ground state of La0.85Sr0.15CoO3, which is often debated based on phase separation issues. We report the results of two samples of La0.85Sr0.15CoO3 (S-1 and S-2) prepared under different conditions. Neutron depolarization, higher harmonic ac susceptibility and magnetic relaxation studies were carried out along with conventional magnetometry measurements to differentiate subtle changes at the microscopic level. There is no evidence of ferromagnetic correlation in the sample S-2 attributed to a spin-glass phase, and this is compounded by the lack of existence of a second order component of higher harmonic ac susceptibility and neutron depolarization. A magnetic relaxation experiment at different temperatures complements the spin glass characteristic in S-2. All these signal a sharp variance when we consider the cluster-glass-like phase (phase separated) in S-1, especially when prepared from an improper chemical synthesis process. This shows that the nonlinear ac susceptibility is a viable tool to detect ferromagnetic clusters such as those the neutron depolarization study can reveal.

Coexistence of interacting ferromagnetic clusters and small antiferromagnetic clusters in La0.5Ba0.5CoO3

We report detailed dc magnetization and linear and nonlinear ac susceptibility measurements on the hole doped disordered cobaltite La0.5Ba0.5CoO3. Our results show that the magnetically ordered state of the system consists of coexisting non-ferromagnetic phases along with percolating ferromagnetic clusters. The percolating ferromagnetic clusters possibly start a magnetic ordering at the Curie temperature of 201.5(5) K. The non-ferromagnetic phases mainly consist of antiferromagnetic clusters with size smaller than the ferromagnetic clusters. Below the Curie temperature the system exhibits an irreversibility in the field cooled and zero field cooled magnetization and a frequency dependence in the peak of ac susceptibility. These dynamical features indicate the possible coexistence of spin-glass phase along with ferromagnetic clusters similar to La1−xSrxCoO3 (x ≥ 0.18), but the absence of field divergence in the third harmonic of ac susceptibility and zero field cooled memory clearly rule out any such possibility. We argue that the spin-glass phase in La1−xSrxCoO3 (x ≥ 0.18) is associated with the presence of incommensurate antiferromagnetic ordering in non-ferromagnetic phases, which is absent in La0.5Ba0.5CoO3. Our analysis shows that the observed dynamical features in La0.5Ba0.5CoO3 may be due to progressive thermal blocking of ferromagnetic clusters, which is further confirmed by Wohlfarth’s model of superparamagnetism. The frequency dependence of the peak of ac susceptibility obeys the Vogel–Fulcher law with τ0 ≈ 10−9 s. This together with the existence of an AT-line in H–T space indicates the presence of significant inter-cluster interaction among these ferromagnetic clusters.

The 3rd Harmonic AC Susceptibilities in the Grain Model of High-Tc Superconductors

AC susceptibility measurement has been widely used to investigate the magnetic properties of high-Tc superconductors which is composed of the grains and their interconnecting links. Transport critical current density is low because of a grain structure. The fundamental AC susceptibility of the superconductors with the grain structure has been successfully simulated using the critical state model by Irie and Yamafuji and gave separately the critical current densities in both intra- and inter- grains. The 3rd harmonic AC susceptibilities with a real part χ3’ and an imaginary part χ3” are numerically calculated in the grain model to get more clear insight of the grain-link structure. The double peaks and the multi-transitions also appear in the simulated curves. The simulated results are satisfactorily compared with the measured characteristics of Sm-123 superconductors to give pinning penetration fields Bpg and Bpl of the grain and the link. Combining with the crystallographic investigation, the critical current densities Jcg and Jcl in the grain and the link can be estimated.

Successive spin glass, cluster ferromagnetic, and superparamagnetic transitions in RuSr2Y1.5Ce0.5Cu2O10 complex magneto-superconductor

We report structural, DC magnetization, detailed linear/non-linear AC susceptibility, (with applied frequency and amplitude) isothermal and thermoremanent magnetization (TRM) behavior for RuSr2Y1.5Ce0.5Cu2O10 (YRu-1222) magneto-superconductor to understand its complex magnetism. Studied sample is synthesized through the novel solid state high pressure (6 GPa) high temperature (1450 °C) (HPHT) technique. The compound is crystallized in tetragonal structure with space group I4/mmm (No. 139). DC magnetic susceptibility shows that studied YRu-1222 is magneto-superconducting with Ru spins magnetic ordering at around 110 K and superconductivity (SC) in the Cu-O2 planes below ~ 30 K. Frequency and field dependent detailed AC magnetic susceptibility measurements confirms the spin-glass (SG) behavior with homogeneous/non-homogeneous ferromagnetic (FM) clusters in this system. Variation of cusp position with applied AC frequency follows the famous Vogel-Fulcher law, which is commonly accepted feature for spin-glass (SG) system with homogeneous/non-homogeneous ferromagnetic clusters embedded in spin-glass (SG) matrix. Above the freezing temperature (T f ), first and third harmonics AC susceptibility analysis indicated possibility of the co-existence of spin cluster ferromagnetism with superparamagnetism (SPM). The M-H loops at low temperature exhibit the ferromagnetic behavior with rather small coercive field (H c ) and remnant magnetization (M r ). Summarily, the magnetic (DC and AC) susceptibility measurements and their analysis have enabled us to unearth the complex magnetism in terms of successive SG-FM-SPM transitions with temperature.

Influence of different pinning ability on harmonic susceptibilities in high-temperature superconductors

Influence of flux pining ability in the intragrain characterized by critical current density on the harmonics AC susceptibility is studied. A sintered superconducting sample is described by alternating weak (intergrains or weak links) and strong (intragrains) regions, which is depicted by different critical current densities Jcw and Jcs. Simulations using the flux creep model show that with the increase of the flux pinning ability of the intragrain region, a step and two peaks in the fundamental AC susceptibility as well as more peaks in the higher order even and odd harmonics are observed. Moreover, the Coles–Coles plot of χ3 may be used as a method to qualitatively estimate the values of Jc0s/Jc0w.

Evidence of electronic phase arrest and glassy ferromagnetic behaviour in (Nd0.4Gd0.3)Sr0.3MnO3 manganite: comparative study between bulk and nanometric samples

The effect of the doping of rare earth Gd3+ ions replacing Nd3+ in Nd0.7Sr0.3MnO3 is investigated in detail. Measurements of resistivity, magnetoresistance, magnetization, and linear and nonlinear ac magnetic susceptibility on chemically synthesized (Nd0.7−xGdx)Sr0.3MnO3 show various interesting features with doping level x = 0.3. A comparative study has been carried out between a bulk and a nanometric sample (grain size ∼60 nm) synthesized from the same as a prepared powder to maintain an identical stoichiometry. The resistivity of the samples shows strong dependence on the magnetic field–temperature history. The magnetoresistance of the samples also shows strong irreversibility with respect to sweeping of the field between the highest positive and negative values. Moreover, the resistivity is found to increase with time after field cooling and then switching off the field. All these phenomena have been attributed to phase separation effects and the arrest of phases in the samples. Furthermore, the bulk sample displays a spin glass like behaviour as evident from the frequency dependence of linear ac magnetic susceptibility and critical divergence of the nonlinear ac magnetic susceptibility. The experimentally obtained characteristic time τ0 after dynamical scaling analysis of the frequency dependence of the ac susceptibility is found to be 10−17 s which implies that the system is different from a canonical spin glass. An unusual frequency dependence of the second harmonic of ac susceptibility around the magnetic transition temperature led us to designate the magnetic state of the sample to be glassy ferromagnetic. On reduction of the grain size low field magnetoresistance and phase arrest phenomena are found to enhance but the glassy state is observed to be destabilized in the nanometric sample.

Study of spin glass and cluster ferromagnetism in RuSr2Eu1.4Ce0.6Cu2O10-δ magneto superconductor

We report DC magnetization, detailed systematic linear and nonlinear AC magnetic susceptibility and transport for a single phase RuSr2Eu1.4Ce0.6Cu2O10-δ (EuRu-1222) magneto-superconductor. The studied sample is synthesized through standard solid state reaction route, which is crystallized in single phase tetragonal structure with space group I4/mmm. DC magnetic susceptibility measurements revealed that the studied EuRu-1222 is a magneto-superconductor with Ru spins ordering at around 110 K and superconductivity in the Cu-O2 planes below ≈ 30 K. Temperature dependence of AC susceptibility with different frequency and amplitude variations confirms spin-glass behavior with cluster ferromagnetism of the system. Change in the cusp position with frequency follows the Vogel-Fulcher law, which is commonly accepted feature for a spin-glass (SG) system with ferromagnetic clusters. The third harmonic of AC susceptibility (χ3) shows that the system undergoes a spin glass transition below 80 K. Superconducting transition temperature (Tc) onset and ρ = 0 are seen at around 30 and 18 K without any applied field and the same decreases to 10 and 2 K under 130 kOe applied field. Also low fields isothermal (MH) suggests that ferromagnetic clusters are embedded in spin-glass (SG) matrix. The magnetization versus applied field (MH) loops exhibited ferromagnetic (FM) like behavior with rather small coercive fields. Detailed AC magnetic susceptibility measurements are carried out to unearth the short range magnetic correlations. These results support the spin-glass (SG) formation followed by ferromagnetic clustering effects at low temperatures. Our detailed magnetization and magneto transport results will undoubtedly contribute to current understanding of the complex magnetism of the EuRu-1222 system.

PRESS-MAG-O: a unique instrument to probe materials and phenomena under extreme conditions at Frascati

PRESS-MAG-O is a new instrument under commission at the Laboratori Nazionali di Frascati of the Istituto Nazionale di Fisica Nucleare (INFN) designed to investigate materials under extreme conditions. The instrument, once completed, will allow combining high harmonic AC magnetic susceptibility measurements and magneto-optic experiments on samples under high pressures (HP), with a variable DC magnetic field in a wide temperature range. The system is designed to work at SINBAD, the IR synchrotron radiation beamline operational since 2001 at DAΦNE (Double AnnularΦ-factory for Nice Experiments), the storage ring of the Laboratori Nazionali di Frascati of the INFN. HP will be applied up to about 20 GPa to samples inside a Cu–Be diamond anvil cell designed to allow concurrent FTIR experiments and high harmonic AC susceptibility measurements in a DC magnetic field up to 8 T and in a wide temperature range.

Spin-glass behavior and magnetocaloric effect in melt-spun TbCuAl alloys

Magnetic properties and magnetocaloric effects of amorphous and crystalline TbCuAl ribbons are investigated by measuring their ac susceptibilities including a nonlinear term and dc magnetizations. The in-phase third harmonic ac susceptibility χ3′ is found to be negative. It can be well fitted by the expression χ3′=τε3γ at high temperatures, indicating a spin-glass behavior in amorphous TbCuAl alloy. ΔTf(ω)/[Tf(ω)Δlog10ω], a possible distinguishing criterion to judge the presence of a spin-glass behavior is ∼0.011. The frequency-dependent data can be well fitted by the conventional critical slowing down law and the spin-glass transition temperature is obtained to be 20.1 K. The maximum of magnetic entropy change reaches 4.5 J kg−1 K−1 for a field change of 0–50000 Oe, while the crystalline TbCuAl compound experiences a simple ferromagnetic-to-paramagnetic phase transition. The peak value of magnetic entropy change is obtained at the Curie temperature and reaches 14.4 J kg−1 K−1 for the same field change, which is much larger than that of amorphous TbCuAl alloy.

Doping dependence of irreversibility line in Y 1−xCa xBa 2Cu 3O 7−δ

The irreversibility lines (IL) for series of Y 1− x Ca x Ba 2Cu 3O 7− δ ( x = 0.025; 0.10 and 0.20) polycrystalline samples with different overdoping were investigated. The irreversibility fields were determined from measurements of third harmonics AC susceptibility as a function of DC field at constant temperature. For the weakly overdoped sample (with x = 0.025) H irr(77 K) is about 7 T, which is higher than the previously reported for the non-substituted one. The irreversibility line behavior is typical for glass–liquid phase transition and this is confirmed by transport measurements. On increasing the overdoping the irreversibility fields were shifted towards lower temperatures. The behavior of H irr( T) for the highly overdoped sample (with x = 0.20) is influenced by the surface barrier effect. It is supposed that in highly overdoped specimen the process of phase separation is enhanced and the Fermi clusters grow in size. This leads to a suppression of the bulk pinning and to a domination of the surface barrier effects and flux creep as well. As a confirmation, the obtained quadratic J c ( T) dependences were presented demonstrating the existence of S–N–S type inter-grain joints in the highly overdoped samples.

Coexistence of ferromagnetism and cluster glass state in superconducting ferromagnet RuSr2Eu1.5Ce0.5Cu2O10−δ

Systematic dc and ac magnetic susceptibility measurements performed on RuSr2Eu1.5Ce0.5Cu2O10−δ (Ru1222) demonstrate a paramagnetic to ferromagnetic transition around 95 K. The third harmonic of the ac susceptibility reveals that the system undergoes a spin glass transition below 75 K. The features of the zero-field cooled and field cooled dc magnetization curves of Ru1222 material resemble those of a cluster glass state, rather than those of a canonical spin glass state. The magnetization versus applied field loops do not saturate, even at very high applied fields, resulting in the short range magnetic order in the system, which facilitates the formation of clusters that freeze at low temperature. The temperature dependence of the second and third harmonic ac susceptibilities further confirms the coexistence of a cluster glass state and ferromagnetic order in the Ru1222 system.

AC-Susceptibility study on vortex-molecule lattice in supermultilayer cuprate HgBa 2Ca n-1 Cu nO 2 n+2+ δ ( n = 14)

We investigated that in HgBa 2Ca n-1Cu nO 2n+2+ δ [Hg-12( n-1) n], for n ⩾ 6, T c of about 105 K, vortex melting lines remains constant and independent of number of inner plane CuO 2 layers. However the vortex dynamics of the supermultilayer system could be crucially different from that of single or double layer cuprates. Therefore we measured the fundamental and third harmonic AC susceptibility responses to see the vortex dynamics and vortex matter phase diagram of Hg-12( n-1) n ( n = 14), the higher member of super-multilayered cuprate superconductors. The Lindemann type vortex melting line was estimated using onset of third harmonic susceptibility ( χ 3), at very low h AC (50 mOe), and represented by 3D Ginzburg Landau rescaling. Frequency dependence of out of phase susceptibility χ″(T) measured at lower fields of 500 and 1000 Oe, for 10 Hz to 10 kHz, showed resonance behaviour in the temperature region 55–68 K, suggesting rotational and translational creep dynamics of vortex molecule, even below usual melting line. We present schematic vortex phase diagram, considering the response of vortex dynamics to applied AC frequencies, taking into account the crossover temperatures obtained from critical slowing down of spin glass model and extended thermal activated model.

PRESS-MAG-O: A new facility to probe materials and phenomena under extreme conditions

In the recent years, several experiments performed under high magnetic fields (HMFs), at high pressure (HP) and/or at low temperature (LT) have led to spectacular discoveries in condensed matter. In many new systems, although challenging, it is strategic to perform a magneto-optical analysis, to investigate the phonon behavior in the far infrared (IR) domain. By combining HMF and HP in a wide temperature ( T) range to perform concurrently IR magneto-optics and ac-magneto-dynamic experiments, it will be possible to achieve unique information on systems and/or new phenomena, almost impossible to obtain with standard spectroscopic methods. Here we present PRESS-MAG-O, a new facility under construction that will perform HP experiments under HMF in a wide T range. The system is expected to be operational by the end of 2008 and will be tested at SINBAD, the IR synchrotron radiation beamline operational since 2001 at DAΦNE (Double Annular Φ-factory for Nice Experiments), the storage ring of the INFN Frascati National Laboratory (LNF). While for IR experiments an interferometer will be used, for the magneto-dynamic experiments a SQUID magnetometer in the 10 Hz–2 KHz frequency range will be utilized. HP will be applied to samples by a Cu–Be diamond anvil cell (DAC), so that the device will be able to collect FTIR spectra and high harmonic ac susceptibility data in a dc magnetic field up to 8 T and to about 20 GPa in a wide temperature range (4.2–200 K).

Quasi-2D characteristics in the ac susceptibility response of polycrystalline (Bi,Pb)SrCaCuO/2223 multiphase systems

Fundamental and third harmonic ac susceptibility measurements as a function of temperature T, ac magnetic field, and dc magnetic field have been performed on Bi(Pb)SrCaCuO/2223 bulk samples consisting of both Bi2Sr2Ca2Cu3O10+δ (2223) and Bi2Sr2CaCu2O8+δ (2212) phases. Since the χ1″(T) peak corresponding to the losses in the weak links between the grains shifts rapidly to lower T and its amplitude is strongly suppressed with increasing the dc magnetic field Hdc, the other peaks related to the losses in the grains become visible. For the samples consisting of single phase 2223, these intragranular peaks are situated near 38K, 58K, and 80–88K (depending on the sample), whereas for the samples consisting of single phase 2212, they are situated near 20K, 43K, and 77K. For Hdc⩾1kOe, the temperature positions of the intragranular peaks are weakly field dependent. This shows that the transition line determined from the loss peaks behaves like the melting line in two-dimensional (2D) systems. Also, as the field increases, the amplitude of the loss peaks can decrease up to their disappearance, suggesting a layer decoupling process. In this way, we show that, above a crossover field of ∼1kOe, the vortex lattice in the superconducting grains of polycrystalline samples reproduces the behaviour of the vortex lattice in a quasi-2D object consisting of a set of separated “thin films” with one-, two-, and three-effective-layer thicknesses. For the samples consisting of both 2223 and 2212 phases, three additional peaks were observed, situated near 28K, 50K and 75–80K (depending on the sample). These peaks were attributed to the regions in which the 2212 and 2223 layers alternate.