Ac Susceptibility Studies Research Articles

Emergent order in the spin-frustrated systemDyxTb2−xTi2O7studied by ac susceptibility measurements

We report the ac susceptibility study of ${\text{Dy}}_{x}{\text{Tb}}_{2\ensuremath{-}x}{\text{Ti}}_{2}{\text{O}}_{7}$ with $x∊[0,2]$. In addition to the single-ion effect at ${T}_{s}$ (single-ion effect peak temperature) corresponding to the ${\text{Dy}}^{3+}$ spins as that in spin ice ${\text{Dy}}_{2}{\text{Ti}}_{2}{\text{O}}_{7}$ and a possible spin freezing peak at ${T}_{f}$ $({T}_{f}<3\text{ }\text{K})$, a new peak associated with ${\text{Tb}}^{3+}$ is observed in ${\ensuremath{\chi}}_{\text{ac}}(T)$ at nonzero magnetic field with a characteristic temperature ${T}^{\ensuremath{\ast}}$ $({T}_{f}<{T}^{\ensuremath{\ast}}<{T}_{s})$. ${T}^{\ensuremath{\ast}}$ increases linearly with $x$ in a wide composition range ($0<x<1.5$ at 5 kOe). Both application of a magnetic field and increasing doping with ${\text{Dy}}^{3+}$ enhance ${T}^{\ensuremath{\ast}}$. The ${T}^{\ensuremath{\ast}}$ peak is found to be thermally driven with an unusually large energy barrier as indicated from its frequency dependence. These effects are closely related to the crystal-field levels and the underlying mechanism remains to be understood.

Structural, electrical, magnetic, elastic and anelastic behaviour of

Abstract With a view to understanding the structural, electrical and magnetic, elastic and anelastic behaviour of charge ordered Nd 0.6 Ca 0.4 MnO 3 , systematic investigations were undertaken. The sample was synthesized by a sol–gel route. The sample was characterized by X-ray diffraction (XRD) using a Rietveld refinement technique and was found to have orthorhombic structure with space group Pnma . A study on the variation of electrical resistivity with temperature has been carried out in the range 100–300 K and it was found to exhibit a field induced transition. The ac susceptibility studies show two transition temperatures, which are attributed to charge ordering and a Neel transition. Internal friction and longitudinal modulus studies were carried out using the composite oscillator technique. An effort has been made to explain the observed anomalous behaviour by a qualitative model.

Ferromagnetic manganese “cubes”: from PSII to single-molecule magnets

The reaction of Mn(O₂CMe)₂·2H₂O with Me-saoH₂ (Me-saoH₂ = 2-hydroxyphenylethanone oxime) in MeCN forms the complex [Mn(III)₄(Me-sao)₄(Me-saoH)₄] (1) in good yields. Replacing Me-saoH₂ with Naphth-saoH₂ (Naphth-saoH₂ = 2-hydroxy-1-napthaldoxime) in the presence of CH₃ONa forms the complex [Mn(III)₄(Naphth-sao)₄(Naphth-saoH)₄] (2) in low yields, while the reaction between Mn(ClO₄)₂·6H₂O, Et-saoH₂ (Et-saoH₂= 2-hydroxypropiophenone oxime) and NBu₄OH in MeCN gives the complex [Mn(III)₄(Et-sao)₄(Et-saoH)₄] (3) in moderate yields. All three tetrametallic cages exclusively contain Mn(III) centres arranged in a "cube"-like topology, in which the metal centres are connected by -N-O(oximate) groups. The magnetic properties of 1-3 are near identical, revealing the presence of only ferromagnetic interactions between the metal ions leading to high-spin ground states of S = 8. The complexes display frequency dependent out-of-phase signals in ac susceptibility studies and, in the case of 1 single-molecule magnetism has been observed by means of single-crystal hysteresis loop measurements.

AC susceptibility study of superconducting aluminum-doped silicon carbide

In 2007, type-I superconductivity in heavily boron-doped silicon carbide was discovered. The question arose, if it is possible to achieve a superconducting phase by introducing dopants different from boron. Recently, aluminum-doped silicon carbide was successfully found to superconduct by means of resistivity and DC magnetization measurements [1]. In contrast to boron-doped silicon carbide, the aluminum doped system is treated as a type-II superconductor because of the absence of an hysteresis in data measured upon decreasing and increasing temperature in finite magnetic fields. In this paper, results of a recent AC susceptibility study on aluminum-doped silicon carbide are presented. In higher applied DC magnetic fields and at low temperatures, a weak indication of supercooling with a width of a few mK is found. This supports the conclusion that aluminum-doped silicon carbide is located near to the border between type-I and type-II superconductivity, as pointed out in a recent theoretical work, too.

Mn7 and Mn12 Clusters From Use of 2-(Pyridine-2-yl)propan-2-ol: A New Half-Integer Single-Molecule Magnet

The syntheses, crystal structures, and magnetochemical characterization are reported for two new Mn clusters, [Mn(7)O(3)(OH)(3)(O(2)CBu(t))(7)(dmhmp)(4)] (1) and [Mn(12)O(7)(OH)(OMe)(2)(O(2)CPh)(12)(dmhmp)(4)(H(2)O)] (2). They were obtained from the use of 2-(pyridine-2-yl)propan-2-ol (dmhmpH), a more bulky version of the 2-(hydroxymethyl)pyridine (hmpH) reagent commonly employed previously in Mn chemistry. The reaction of dmhmpH with MnCl(2).4H(2)O and NaO(2)CBu(t) in MeCN/MeOH led to the heptanuclear complex 1, whereas the analogous reaction with Mn(O(2)CPh)(2) gave dodecanuclear complex 2. Complexes 1 and 2 are both mixed-valent and are of unprecedented structural types. Complex 1 (Mn(II), 6Mn(III)) can be described as the fusion of butterfly-like [Mn(4)(mu(3)-O)(2)] and tetrahedral [Mn(4)(mu(4)-O)] units by the sharing of a common Mn atom. Complex 2 (3Mn(II), 9Mn(III)) possesses a central [Mn(4)O(6)] face-sharing incomplete dicubane, on either side of which is a tetrahedral [Mn(4)(mu(4)-O)] unit attached to the oxide ions of the former. Solid-state dc and ac magnetic susceptibility measurements on 1 and 2 establish that they possess unusual S = 7/2 and 13/2 ground states, respectively. The ac susceptibility studies on 2 revealed nonzero frequency-dependent out-of-phase (chi(M)'') signals at temperatures below 3 K, indicating a single-molecule magnet (SMM). Magnetization versus applied dc field sweeps on single crystals of 2.3CH(2)Cl(2) down to 0.04 K exhibited hysteresis, thus confirming complex 2 to be a new half-integer SMM.

Magnetization studies on ɛ-Fe 2.4Co 0.6N nanoparticles

ɛ-Fe 2.4Co 0.6N nanoparticles are prepared by nitridation of ultrafine iron–cobalt oxide in NH 3 gas atmosphere at 873 K for 3 h. Their magnetic properties are studied using ac and dc magnetization techniques. Two peaks at 69 and 151 K are found in ac susceptibility study. The former peak is assigned to superparamagnetic blocking temperature ( T B ∼ 69 K), whereas the origin of the latter one could not be ascertained since it is observed only from imaginary part of ac susceptibility study. The positions of peaks are found to be dependent on the applied fields and frequencies. Also, dc magnetization studies corroborate T B . Anisotropy constant ( K a ) is found to be 2.3 × 10 5 erg/cm 3. The peaks disappear at high-applied field due to the overcome of applied filed over anisotropic energy. Ferromagnetic domains rotate incoherently. At low temperature, Bloch law cannot be applied, but Curie law can be applied above T B . Interestingly, spin relaxation is faster at 10 K as compared to that at 70 K indicating the presence of frustration of spins at lower temperature.

Pinning potential in thick PrBa 2Cu 3O x/YBa 2Cu 3O 7−δ quasi-multilayers

Using Pulsed Laser Deposition we have fabricated thick quasi-multilayers composed of incomplete layers of PrBa 2Cu 3O x (PrBCO) nano-dots and layers of YBa 2Cu 3O 7− δ (YBCO). The number of such sequences was between 2 and 6, with the thickness of individual YBCO layers between 565 and 885 nm, and total thickness between 1.13 and 5.31 μm. For the thinner quasi-multilayer, DC magnetization studies showed an increase in the critical current density J c at all fields in comparison with a pure YBCO reference sample, while the thicker samples showed an increased J c only in high fields. We have also investigated the frequency dependence of J c from AC susceptibility studies and found that the pinning potential is well described by a logarithmic dependence on current density. Pinning potentials in PrBCO/YBCO quasi-multilayers also proved to be higher than in the reference sample at high fields. From angle-dependent transport measurements we have found indications of strong pinning centres induced by the (PrBCO) nano-dots, both isotropic and c-axis correlated.

Mn4, Mn6, and Mn11 Clusters from the Use of Bulky Diphenyl(pyridine-2-yl)methanol

The synthesis, crystal structure, and magnetochemical characterization are reported of three new Mn clusters [Mn(4)O(2)(O(2)CBu(t))(5)(dphmp)(3)] (1), [Mn(6)O(4)(OMe)(2)(O(2)CPh)(4)(dphmp)(4)] (2), and [Mn(11)O(7)(OMe)(7)(O(2)CPh)(7)(dphmp)(4)(MeOH)(2)] (3). They were obtained from the use of diphenyl(pyridine-2-yl)methanol (dphmpH), a bulkier version of the 2-(hydroxymethyl)pyridine (hmpH) reagent commonly employed previously in Mn chemistry. The reaction of dphmpH with MnCl(2) x 4 H(2)O and NaO(2)CBu(t) in MeCN/MeOH (30 mL, 5:1 v/v) led to the isolation of tetranuclear complex 1, whereas the analogous reaction with NaO(2)CPh gave hexanuclear complex 2. When the 5:1 solvent ratio in the latter reaction was changed to 1:29, the isolated product was now undecanuclear complex 3. Complexes 1-3 all possess rare or unprecedented Mn(x) topologies: Complex 1 possesses a [Mn(4)(mu(3)-O)(2)](8+) (4 Mn(III)) butterfly core, one edge of which is additionally bridged by an alkoxide arm of a dphmp(-) chelate; complex 2 possesses a [Mn(6)(mu(4)-O)(2)(mu(3)-O)(2)(mu(3)-OMe)(2)](8+) (6 Mn(III)) core with a face-sharing double cubane topology; and complex 3 (Mn(II), 10 Mn(III)) possesses a [Mn(4)(mu(4)-O)(3)(mu(3)-OMe)](5+) cubane unit, attached on one side to a Mn(II) atom by a mu(4)-O atom and alkoxide groups, and on the other side to a [Mn(5)(mu(4)-O)(mu(3)-O)(3)(mu(3)-OMe)(mu-OR)(3)](3+) unit consisting of three face-sharing defective cubanes linked to an additional Mn(III) atom by a mu(3)-O atom. Solid-state dc and ac magnetic susceptibility measurements on 1-3 establish that they possess S = 0, 3, and 5/2 ground states, respectively. ac susceptibility studies on 2 and 3 reveal weak non-zero frequency-dependent out-of-phase (chi(M)'') signals at temperatures below 3 K, possibly indicative of single-molecule magnets with very small barriers. The combined results demonstrate a ligating difference between bulky dphmp(-) and hmp(-), and the resulting usefulness of the former to provide access to a variety of Mn(x) molecular species not known with the latter.

Observation of reentrant spin glass behavior inLaCo0.5Ni0.5O3

The magnetic and transport properties of LaCo0.5Ni0.5O3 have been studied. The dc magnetization and the ac susceptibility studies suggest the presence of a magnetic-phase transition from a ferromagnetic (FM) to a spin glass phase at a low temperature. This type of reentrant spin-glass (RSG) behavior attached to a long-range ordered ferromagnet is observed in this system. A magnetoresistance of ~10% is observed at 5 K which is unsaturated up to 11 Tesla suggests the presence of antiferromagnetic (AFM) interactions. It is likely that the competition between such AFM interactions with FM interactions yield an RSG phase.

Magnetic properties and magnetoelectric (ME) effect in ferroelectric rich Ni 0.2Co 0.8 Fe 2O 4 + PbZr 0.8Ti 0.2O 3 ME composites

Magnetoelectric composites with composition ( x) Ni 0.2Co 0.8Fe 2O 4 (ferrite) + (1 − x)PbZr 0.8Ti 0.2O 3 (ferroelectric) in which x varies as 0.0, 0.15, 0.30, 0.45 and 1.0 mol% have been prepared by double sintering ceramic method. The X-ray diffraction pattern of the composites reveals the formation of spinel structure for the ferrite phase and perovskite structure for the ferroelectric phase without any other phase formation. Scanning electron micrographs (SEM) were taken to understand the microstructure and grain size of the samples. The estimated values of the porosity of the samples lie between 4.5% and 16.2%. Hysteresis measurements were used to determine saturation magnetization ( M s) and magnetic moment ( μ) and the variations of saturation magnetization and magnetic moment were interpreted in terms of the composition of the samples. From AC susceptibility studies the contribution of both single domain (SD) particle of the ferrite phase and mixed (MD + SD) particle of the composites in ME output was discussed. The magnetoelectric voltage coefficient (d E/d H) H was measured as a function of DC magnetic field and the maximum value of ME conversion factor was observed (828 μV cm −1 Oe −1) for the composite with 15% ferrite and 85% ferroelectric phase.

Electron spin resonance and AC susceptibility studies on La 0.9Pb 0.1MnO 3 single crystals

Phase separation has been recognized as important properties of manganite to create colossal magnetoresistance (CMR). Frequency dependence of AC susceptibility and electron spin resonance (ESR) studies confirm the phase separated glassy magnetism in the La 0.9Pb 0.1MnO 3 crystals. ESR spectra exhibit a gradual narrowing of the asymmetric FMR signals upon increasing the temperature and approaching the Curie temperature ( T c) . The temperature dependence of line width (Δ H pp), g-factor, double integrated ( I) intensity of the resonance signals and frequency dependence peak temperatures are discussed in this paper to explain inhomogeneity in the La 0.9Pb 0.1MnO 3 single crystals.

Reentrant-spin-glass state inNi2Mn1.36Sn0.64shape-memory alloy

The ground state properties of the ferromagnetic shape memory alloy of nominal composition Ni2Mn1.36Sn0.64 have been studied by dc magnetization and ac susceptibility measurements. Like few other Ni-Mn based alloys, this sample exhibits exchange bias phenomenon. The observed exchange bias pinning was found to originate right from the temperature where a step-like anomaly is present in the zero-field-cooled magnetization data. The ac susceptibility study indicates the onset of spin glass freezing near this step-like anomaly with clear frequency shift. The sample can be identified as a reentrant spin glass with both ferromagnetic and glassy phases coexisting together at low temperature at least in the field-cooled state. The result provides us an comprehensive view to identify the magnetic character of various Ni-Mn-based shape memory alloys with competing magnetic interactions.

Phase separation versus spin glass behavior in La0.85Sr0.15CoO3

We present comprehensive studies of dc magnetization, ac susceptibility, and magnetotransport of two sets of La0.85Sr0.15CoO3 samples, one exhibits phase separation and the other exhibits spin glass behavior. Our study reveals that the phase separation in La0.85Sr0.15CoO3 is neither inherent nor ubiquitous; rather, it is a consequence of preparation condition. It is realized that the low temperature annealed sample exhibits phase separation while the high temperature annealed one shows the characteristic of spin glass behavior. This study shows that the most probable magnetic state of La0.85Sr0.15CoO3 is spin glass.

AC susceptibility studies of grain-aligned superconductors by grained Bean model

AC susceptibility of low-Tc metallic superconductors shows smooth transition in the in-phase χ' and a peak in the out-phase χ". High-Tc oxide superconductors with anisotropic and grain-textured structures show deformed complex characteristics, such as double peaks in χ" and shoulders in χ'. Instead of simple Bean model, a grained Bean model, where the superconducting grains is immersed in weak superconducting matrix, are proposed. The susceptibilities numerically analyzed using the grained Bean model show varied and deformed curves as observed in the high-Tc superconductors. From the dependence of χ' and χ" on temperatures T and DC magnetic fields Bdc in grain-aligned Hg(Re)-1223 superconductors, textures of grains and interconnecting links and their grain-aligned nature can be estimated.

Low-field AC susceptibility study of the flux motion in Bi2Sr2CaCu2Oy thin films

DC magnetron sputtering technique were used for the synthesis of high quality epitaxial thin films of the superconducting cuprate Bi2Sr2CaCu2Oy (Bi: 2212) thin films. The structural characterization carried by X-ray diffraction indicates that the films are single phase and oriented with their c-axis perpendicular to the substrate surface. The flux motion mechanisms in the vicinity of the irreversibility line have been studied by AC susceptibility technique. The temperature dependencies of real and imaginary parts of AC susceptibility were performed, by using different values of amplitude and frequency. Temperature dependence and low field dependence of the activation energy for flux motion were obtained

Ac susceptibility studies of magnetic relaxation in nanoparticles of Ni dispersed in silica

Temperature dependence of ac susceptibilities χ′ and χ″ are reported using frequencies fm=0.1, 1, 99, 499, and 997 Hz for nanoparticles of Ni dispersed in silica (Ni/SiO2:15/85) with the mean sizes D=3.8, 11.7, 15, and 21 nm (σ≃0.2 nm), as determined by transmission electron microscopy. The blocking temperatures TB, as determined by peaks in χ″ versus T data, are fit to the Vogel–Fulcher law based on the following equation: TB=To+Ta/ln(fo/fm). Using the attempt frequency fo=1.82×1010 Hz, Ta (K)=310 (21), 954(17), 1334(14), and 1405(47) are determined for D=3.8, 11.7, 15, and 21 nm, respectively, along with To (representing the interparticle interaction)=0, 0, 6.6(0.7), and 12.5(2.5) K respectively. The magnitudes of Ta=KaV/k yield the anisotropy constant Ka increasing with decreasing D (or volume V) due to contributions from surface anisotropy. The validity of the theoretical result χ″=C∂(χ′T)/∂T with C≃π/[2 ln(fo/2πfm)] is checked and the calculated values of fo are consistent with experimental value of fo=1.82×1010 Hz.

Cluster-glass behavior of a highly oxygen deficient perovskite,BaBi0.28Co0.72O2.2

A highly oxygen deficient perovskite,BaBi0.28Co0.72O2.2, was synthesized by solid state reaction. The crystal structure was determined by means ofneutron and x-ray powder diffraction. The material exhibits semiconducting behaviorwith an energy gap of 1.8 eV. The electron diffraction study does not reveal longrange Bi:Co ordering; instead it shows the existence of short range ordering inthis phase. The AC and DC magnetic susceptibility studies reveal cluster-glassbehavior, which has its origin in the interacting ferromagnetic clusters present.

Particle blocking and carrier fluid freezing effects on the magnetic properties of Fe3O4-based ferrofluids

We report the systematic dc and ac susceptibility studies on the particle blocking and carrier fluid freezing effects on the magnetization and relaxation processes in two different ferrofluids composed of Fe3O4 nanoparticles (mean size of ∼14 nm) suspended in hexane and dodecane, which respectively have freezing temperatures below (178 K) and above (264 K) the blocking temperature of magnetic nanoparticles (∼200 K). Experimental results reveal that these effects play a key role in the formation of glasslike peaks and magnetic anomalies in ferrofluids. Quantitative fits of the frequency dependent ac susceptibility to the Vogel–Fulcher model τ=τo exp[Ea/k(T−To)] clearly indicate that the blocking of magnetic nanoparticles in the frozen state significantly affects the interparticle dipole-dipole interaction, causing characteristic spin-glass-like dynamics.

Anomalous magnetic properties in Ni50Mn35In15

We present here a comprehensive investigation of the magnetic ordering in Ni50Mn35In15 composition. A concomitant first order martensitic transition and the magnetic ordering occurring in this off-stoichiometric Heusler compound at room temperature signify the multifunctional character of this magnetic shape memory alloy. Unusual features are observed in the dependence of the magnetization on temperature that can be ascribed to a frustrated magnetic order. It is compelling to ascribe these features to the cluster type description that may arise due to inhomogeneity in the distribution of magnetic atoms. However, evidence is presented from our ac susceptibility, electrical resistivity and dc magnetization studies that there exists a competing ferromagnetic and antiferromagnetic order within the crystal structure of this system. We show that excess Mn atoms that substitute the In atoms have a crucial bearing on the magnetic order of this compound. These excess Mn atoms are antiferromagnetically aligned to the other Mn, which explains the peculiar dependence of magnetization on temperature.

A special sample holder for AC susceptibility measurements of superconducting samples inhigh magnetic fields at various temperatures

The study of AC susceptibility in high magnetic fields is important for some applications,e.g. the investigation of AC losses in the conductors for fusion machines. AC susceptibilitymeasurements for these purposes require a measurement set-up designed for a wide range ofmagnetic fields and temperatures. A sample holder is a significant part of such a set-up.The sample holder described in this article includes: a primary AC coil, a measurementcoil, compensation coils, and a position adjustable insert. The insert contains a Cernoxthermometer for the temperature measurement and a Hall probe for the magnetic fieldmeasurement. Depending on the cooling power, the maximum AC magnetic field amplitudeis between 50 and 90 mT, and the transfer function of the primary AC coil is14.7 mT A−1. The compensation of a pure inductive signal is better than 99.75% and the sample spacediameter is 10 mm. Due to the adjustable position of the insert this sample holder allowedus to measure wires and tapes of different thickness. Our experimental set-up enables us todetermine AC susceptibility in the temperature range 1.5–300 K at magnetic fields up to14 T. An example of measurements on a YBCO-coated conductor is presented aswell.