Ac Magnetic Susceptibility Measurements Research Articles

Large magnetoresistance and charge transfer between the conduction and magnetic electrons in layered oxyselenide BiOCu0.96Se

The electrical and magnetic properties of slightly Cu-deficient BiOCu(0.96)Se have been investigated using neutron and X-ray diffraction, ac magnetic susceptibility, magnetization and electric resistivity measurements. The layered BiOCu(0.96)Se crystallizes into a tetragonal lattice with a P4/nmm symmetry. Thermal profiles of the electrical resistivity reveal a semiconductor type behavior, but depart from its course at low temperatures when antiferromagnetic coupling becomes thermally loosened at 140 K. Positive magnetoresistances are obtained at all temperatures studied. With an applied magnetic field of 0.5 kOe, the magnetoresistance reaches 235% at 2 K. It decreases with increasing temperature, but stabilizes to 70% above 60 K. Both ferromagnetic and antiferromagnetic coupling are detected between the Cu spins in the SeCu4 pyramidal blocks, which results in a non-collinear spin arrangement at low temperatures. The antiferromagnetic component becomes disordered above T(N) = 140 K, whereas the ferromagnetic moment persists up to T(C) = 300 K. Interlayer charge transfer between the conduction and magnetic electrons gives rise to an anomaly in the magnetic order parameter.

Transition metals in ZnO nanocrystals: Magnetic and structural properties

Currently, wide-gap ZnO nanoparticles bear important potential application in electro-optical devices, transparent ultraviolet protection films, and spintronic devices. We have studied the magnetic properties of nanocrystals of ZnO(Fe, Co, Mn) prepared by two methods of synthesis. We have used the microwave assisted hydrothermal synthesis and traditional wet chemistry method followed by calcination. The detailed structural characterization was performed by means of X-ray diffraction and micro-Raman spectroscopy measurements. The morphology of the samples was studied by means of SEM and TEM microscopy. The results of systematic measurements of AC magnetic susceptibility as a function of temperature and frequency as well as SQUID magnetization are presented. The SQUID magnetization measurements revealed a clear bifurcation of the FC and ZFC plots. Such behavior suggested superparamagnetic behavior above the blocking temperature. The dynamic magnetic measurements were performed at small AC magnetic field with amplitude not exceeding 5 Oe and different frequency values (from 7 Hz to 9970 Hz). For ZnO(Fe) and ZnO(Mn), the AC susceptibility maxima has been found for in-phase susceptibility Re(?) and for out of phase susceptibility Im(?). We analyzed the observed frequency dependence of the peak temperature in the AC susceptibility curve using the empirical parameter ? that is a quantitative measure of the frequency shift and is given by the relative shift of the peak temperature per decade shift in frequency, as well as Vogel- Fulcher law. We observed two different types of magnetic behavior, spin-glasslike behavior or superparamagnetic behavior, depending on the synthesis process. For ZnO(Co) nanocrystalline samples high temperature Curie-Weiss behavior in AC magnetic susceptibility was observed. We observed that the determined negative values of the Curie- Weiss temperature ? depend strongly on the nominal content of cobalt oxide. It was shown that for calcination method the values of ? increase with the increase of magnetic ion content indicating enhancement of predominance of antiferromagnetic interactions. For hydrothermal method the opposite effect was observed indicating the breakdown of predominance of aniferromagnetic coupling with the increase of nominal magnetic ion content. This paper gives an in-depth discussion of the structural and magnetic properties of ZnO nanocrystals in addition to the technological issues such as different methods of wet chemical synthesis.

Thickness-driven spin reorientation transition in ultrathin films

We review recent studies by different experimental means of ultrathin films, exhibiting thickness-driven spin reorientation transitions (SRTs). The stage is set by determining, via phenomenological thermodynamic description, of the relevant phase diagrams for the possible types of SRT with and without applied magnetic field. Suitable representation may be chosen such that best use is made of the linear character (under thickness variation) of the system’s path in anisotropy space. The latter involves higher-order bulk and surface anisotropies in a substantial way. We examine sensitive experimental techniques for the detection and quantification of SRTs, such as hysteresis measurements with magneto-optical Kerr effect (MOKE), micromagnetic studies utilizing scanning electron microscopy with polarization analysis (SEMPA), photoemission electron microscopy (PEEM) and spin-polarized low-energy electron microscopy (SPLEEM) as well as ac magnetic susceptibility measurements via MOKE. Key issues are conclusively discussed including the identification of reliable experimental fingerprints about whether a given SRT proceeds via a phase of coexistence or via a cone (canted) phase. We demonstrate how the application of the general theoretical ideas to carefully designed measurements leads to the determination of the most important material parameters in any ultrathin-film SRT, namely, the surface (interface) magnetic anisotropy constants. The review concludes by our personal outline for future promising work on SRTs.

Structural phase transition in one-dimensional bond-alternating antiferromagnet F5PNN

A structural phase transition of pentafluorophenyl nitronyl nitroxide (F5PNN) single crystals with S = 1/2 bond-alternating Heisenberg antiferromagnetic chains has been studied by ac magnetic susceptibility measurements. At the transition around 3 K in zero field, the bond-alternating ratio changes from 0.7 to 0.4 at low temperatures. Thus, the transition is considered to be one of processes from uniform magnetic chain at room temperature to the low-temperature bond-alternating state. The structural transition is likely to have a crystal-size dependence, and in powder sample, continuous deformation is substituted for it. As the applied fields increases until the lower critical field of gapped bond-alternating chains, the transition temperature slightly decreases, which suggests competition between the lattice energy and decreasing internal magnetic energy.

Effect of Substitution and Heat Treatment Route on Polycrystalline FeSe0.5Te0.5 Superconductors

The effect of atomic substitution of Te in iron based superconductors FeSe (1:1 type), which exhibits the simplest crystal structure among the iron-based superconductors, has been investigated in terms of structural, electronic transport, and magnetic properties. Polycrystalline samples with nominal Se:Te in FeSe1−x Te x samples for x=0.5350 °C, 0.5700 °C, 0.6700 °C, and 0.75700 °C were synthesized by the solid-state reaction method. In overall samples, it has been observed that the most superconducting properties seen in x=0.6700 °C samples, for 0.5350 °C and 0.5700 °C samples latter showed better superconducting properties as dc magnetic susceptibility, ac susceptibility, and resistivity measurements and sample homogeneity. T c enhancement is well correlated with the Te substitution up to 75 %.

Field reference technique for ac magnetic susceptibility measurements under pressure

In the present study, we propose a new simple technique based on Faraday low of induction for the ac magnetic susceptibility measurement under high pressure. Although the technique needs a simple additional change from the conventional method, it performs certain separation a real (χ') from imaginary (χ") variable of magnetic susceptibility and free from the change of the ac field amplitude. A typically result obtained from this technique and the shielding effect of ac magnetic field by a pressure cell are shown.

Hydrostatic Pressure Study on 3-K Phase Superconductivity in Sr2RuO4-Ru Eutectic Crystals by AC Magnetic Susceptibility Measurements

We have investigated the effect of hydrostatic pressure on 3-K phase superconductivity in Sr2RuO4-Ru eutectic crystals by means of AC magnetic susceptibility measurements. We have found that the application of hydrostatic pressure suppresses the superconducting transition temperature Tc of the 3-K phase with a pressure coefficient of dTc/dP ≈ −0.2 K/GPa, similar to the case of the 1.5-K phase. We have also observed that the effect of hydrostatic pressure on the 3-K phase seems to be elastic whilst that of uniaxial pressure is plastic.

Structural and magnetic investigation of Fe3+ and Mg2+ substitution into the trigonal bipyramidal site of InGaCuO4

The solid solutions of InGa1−xFexCuO4, InFeCu1−xMgxO4, and InGa1−xFexCu1−xMgxO4 were synthesized and characterized through the use of X-ray and neutron diffraction, and DC—magnetism measurements. All compositions of InGa1−xFexCuO4 are single phase and crystallize in the R3¯m space group, but a transformation to the spinel InFeMgO4 structure was observed for the other series of Fe3+ and Mg2+—rich compounds. As a result of the similar ionic radii for Ga3+ and Fe3+, there was not an obvious change in the c/a ratio for InGa1−xFexCuO4. In the hexagonal domains, the c/a ratio of InFeCu1−xMgxO4 and InGa1−xFexCu1−xMgxO4 showed a linear trend that can be explained by the change in electronic configurations between Cu2+ and Mg2+. All hexagonal compositions display negative Weiss temperatures, and there is an increase in the magnetic transition temperature with the addition of Fe3+. Additional AC magnetic susceptibility measurements for the x=0.4 and 0.6 compositions within the InGa1−xFexCuO4 solid solution show that these transitions are consistent with spin glass behavior, not long range AFM ordering.

Isovalent Substitution and Heat Treatments Control of T c, Chain Oxygen Disorder and Structural Phase Transition in High T c Superconductors (Y1−x Nd x )SrBaCu3O6+z

We report here on the preparation, X-ray diffraction with Rietveld refinement, AC magnetic susceptibility measurements and effect of heat treatments in (Y1−x Nd x )SrBaCu3O6+z . Each sample was subject to two types of heat treatment: oxygen annealing [O] and argon annealing followed by oxygen annealing [AO]. For each x, the [AO] heat treatment increases the orthorhombicity e=(b−a)/(b+a) (for 0≤x<1), T c (for x>0.2) and the distance d[Cu(1)–(Sr/Ba)] (decrease T c) for x<0.25 and decrease it (increase T c) for x>0.25. When x increase from 0 to 1, e decreases to 0 with transition from orthorhombic to tetragonal structure. e[O] decreases with T c[O]. However, T c[AO] decreases with e[AO] until x=0.2, increases for x=0.4 and after it decreases by 9.8 K to 77.2 K for x=1 [AO]. Remarkable correlations were observed between T c(x) and the volume of the unit cell V(x); and between δT c(x)=T c[AO]−T c[O] and δe(x). A combination of several factors such as decrease in d[Cu(1)–(Sr/Ba)]; increase in cationic and chain oxygen ordering; the number p sh(x) of holes by Cu(2)–O2 superconducting plans and in-phase purity for the [AO] samples may account for the observed data.

Magnetism influenced by structural disorder in melt-spun DyMn6 − x Ge6 − x Fe x Al x (x = 2.5, 3)

Different chemical and/or geometrical orders were found in melt-spun DyMn6 − xGe6 − xFexAlx with x = 2.5 and 3 having fully amorphous and mixed (crystalline and amorphous) structure, respectively. Thermal variations in magnetization M from liquid helium up to room temperature for both samples are similar. Magnetization value at zero field cooled curve reaches about 0.1 μB per formula unit at 2 K and then increases. Two maxima are visible, the first at 50 K (a sharp effect) and the second very broad ranging from 150 to 200 K. 57Fe Mossbauer spectrometry investigation revealed a remaining magnetic component in addition to a prevailing quadrupolar feature. Application of a weak external magnetic field causes an increase in the mean hyperfine magnetic field Bhyp and the volume fraction of magnetic component. This observation was confirmed by results of M(T), M(H) and AC magnetic susceptibility measurements. In short-range ordered crystallographic zones characteristic of melt-spun DyMn6 − xGe6 − xFexAlx (x = 2.5, 3) alloys, the related magnetic ordering, called the mictomagnetism or the cluster spin glass appears.

Magnetic, thermodynamic and transport properties at the first and second order magnetic phase transitions in Dy5Si3 compound

We present extended studies including the dc and ac magnetic susceptibility, magnetization, specific heat, electrical resistivity and magnetoresistivity measurements for the Dy5Si3 compound with the hexagonal Mn5Si3-type structure. The results indicate that this compound orders antiferromagnetically below TN=137K. The magnetic properties of Dy5Si3 are mainly governed by the presence of the magnetic moments of Dy3+ ions. In the paramagnetic range, the magnetic susceptibility follows the Curie–Weiss law with μeff=10.57μB/Dy, which is very close to the theoretical value of 10.6μB. From the magnetometric, specific heat and transport data it has been found that below 50K this compound reveals a non-collinear magnetic order, associated with a phase transition, probably of the first order type. On the basis of the thermodynamic approach, we report the magnetocaloric properties in the whole temperature range but concentrate mainly on the region around 50K. The magnetocaloric effect was calculated in terms of the isothermal magnetic entropy change ΔSM as well as the adiabatic temperature change ΔTad using the specific heat data. In spite of the only moderate ΔSM values a significant relative cooling power has been observed.

Magnetic field driven transition from an antiferromagnetic ground state to a ferrimagnetic state in Rb0.19Ba0.3Mn1.1[Fe(CN)6]·0.48H2O Prussian blue analogue

We report a magnetic field dependent (H) antiferromagnetic (AFM) to ferrimagnetic (FIM) transition in Rb0.19Ba0.3Mn1.1[Fe(CN)6]·0.48H2O Prussian blue analogue. A microscopic understanding of the nature of this field induced AFM to FIM transition is achieved by carrying out a low temperature neutron diffraction study under an external magnetic field. A decrease in Néel temperature and an evolution of a ferrimagnetic phase with an increase in dc magnetic field are evident in dc magnetic field dependent ac susceptibility measurements. With an increase in H, the FIM phase grows at the expense of the AFM phase, and for H &amp;gt; 4 T, the system fully transforms to the FIM phase. A magnetic structure consisting of an antiparallel stacking of ferrimagnetic sheets along crystallographic c-direction is proposed for the FIM phase. Based on the results obtained, a phase diagram describing the evolution of both magnetic phases under external magnetic field is presented.

Synthesis and characterization of (Thallium-Tin) doped Bismuth based superconducting materials

Doping with combinations of Tl0.3-xSnx in a certain concentration range enhances the zero resistivity temperature Tc(0) from 104 to 108K. Both high-Tc (2223) and Low-Tc (2212) phases were detected by the X-ray diffraction analysis. However the low-Tc phase is found to dominate over the high-Tc phase with the increase in Sn content. Critical temperatures were determined by the electrical resistivity and ac magnetic susceptibility measurements. Amongst the doped samples studied here a sample containing Sn content of x = 0.06 exhibits comparatively the lowest value of ΔT = 5K, the lowest room temperature resistivity of ρRT = 0.01494 ohm-cm and the highest value of Tc(0) = 108K. Key words: Bismuth based high-Tc superconductors, X-ray diffraction, resistivity, susceptibility

Coordination behavior of sulfamethazine drug towards Ru(III) and Pt(II) ions: Synthesis, spectral, DFT, magnetic, electrochemical and biological activity studies

Ru(III) and Pt(II) complexes of sulfamethazine drug have been synthesized as antibacterial agents, aiming to enhance the biological activity of sulfamethazine drug against resistance development of some organisms and to throw more light about the debatable coordination behavior of sulfamethazine, and their structures were elucidated by several experimental and theoretical tools. Sulfamethazine acts as a bidentate ligand through sulfonamidic (N15) and pyrimidic (N23) nitrogen atoms. AC magnetic susceptibility measurements of RuIII complex showed anti-ferromagnetic behavior in 80–212K with a Néel temperature at 128K. Electrochemical studies revealed that –NH2 and –SO2 groups remain intact in complex formation. Antibacterial activity and structural activity relationship (SAR) showed that activity decreases with complex formation due to increase the energy of lowest unoccupied molecular orbital (ELUMO), dipole moment, and charge on sulfonamidic nitrogen (N15) as a result of formation of covalent M-sulfonamidic bond, which in turn suppress the activity.

Antiferromagnetic Ordering of MII(TCNE)[C4(CN)8]1/2 (M = Mn, Fe; TCNE = Tetracyanoethylene)

The magnetic behaviors of MII(TCNE)[C4(CN)8]1/2 (M = Mn, Fe) prepared from a new synthetic route yielding purer magnetic materials are reported. Detailed DC magnetization and AC magnetic susceptibility measurements reveal that both compounds exhibit magnetic ordering with antiferromagnetic ground states arising from antiferromagnetically coupled ferrimagnetic layers with ordering temperatures of 69 and 84 K for polycrystalline M = Mn (Mn) and Fe (Fe), respectively. Because of the presence of two spin sites, these antiferromagnets are best described as compensated ferrimagnets. A spin flop transition between the antiferromagnetically coupled ferrimagnetic layers occurs at 19 500 Oe at 5 K for Mn, whereas Fe is a metamagnet. Fe also exhibits a constricted hysteretic behavior with a 5 K critical field of 12 600 Oe, and a coercive field and remanent magnetization of 4800 Oe and 1850 emu Oe/mol, respectively.

The electronic phase diagrams of the Eu(Fe0.81Co0.19)2As2 superconductor

The magnetic and superconducting properties of an Eu(Fe0.81Co0.19)2As2 single crystal are investigated by means of ac magnetic susceptibility, dc magnetization, specific heat, transverse resistivity and Hall effect measurements in magnetic fields up to 9 T, applied parallel and perpendicular to the c-axis. The compound exhibits the coexistence of magnetism and superconductivity (SC), characterized by structural distortion (SD) and/or spin-density-wave (SDW) ordering at TSD/SDW = 78 ± 4 K, canted-antiferromagnetic (C-AF) ordering at the Néel temperature TN = 16.5 ± 0.5 K and SC at the critical temperature Tc = 5.3 ± 0.2 K at zero field. Upon applying fields both the C-AF and SC states evolve in an unconventional manner. Magnetic field distinctly affects the spin canting, resulting in separation of the C-AF into two new phases: the C-AF and ferromagnetic (F) ones. The unusual behavior of the SC state produces field-induced SC in the H⊥c configuration as an outcome of the weakening orbital pair-breaking effect. From the experimental data we derive the field-temperature phase diagrams for Eu(Fe0.81Co0.19)2As2. A comparison of experimental results is made with theory developed for type II superconductors and then some important thermodynamic parameters characteristic of the superconducting state of Eu(Fe0.81Co0.19)2As2 are deduced such as the specific heat jump at Tc, ΔCp(Tc)/γnTc, the electron–phonon coupling constant λe–ph, the upper critical field Hc2, coherence length ξ, the Fermi wave-vector kF, effective mass m*, Hall mobility μH, magnetic penetration depth λ and the Ginzburg–Landau parameter κ.

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.

Spin, charge and lattice couplings in Cu-deficient oxysulphide BiOCu0.94S

The electrical and magnetic properties of slightly Cu-deficient BiOCu0.94S are investigated using neutron diffraction, ac magnetic susceptibility, magnetization and electrical resistivity measurements. The Cu spins order in a ferromagnetic arrangement below TC = 250 K. An antiferromagnetic component develops below 180 K when the crystalline unit cell experiences a sharp thermal contraction upon cooling, resulting in a canted ferromagnetic spin arrangement at low temperatures. In the magnetically ordered state the electrical transport can be described using three-dimensional variable range hopping conduction. An applied magnetic field can effectively reduce the hopping barrier. Spin–charge couplings are clearly revealed when the resistivity departs from the hopping conduction and begins to increase with increasing temperatures above 250 K where the Cu spins become disordered.

Suppression of a glassy magnetic state and emergence of a Griffiths-like phase on size reduction in Nd0.8Sr0.2MnO3

A detailed study of the effect of grain size reduction on the spin glass like phase in Nd0.8Sr0.2MnO3 has been carried out. A rigorous measurement of linear and non-linear ac magnetic susceptibility in the bulk-like Nd0.8Sr0.2MnO3 confirms the existence of a glassy phase in the low temperature regime. The effect of size reduction on this glassy state is addressed here. This glassy phase is found to strongly destabilize on reduction of grain size down to a value of 42 nm. Based on our experimental results, the glassy phase has been attributed to the phase separation effect and interaction between the ferromagnetic clusters. The destabilization of this glassy phase has been argued to be due to the modification of the phase separated state on size reduction. Furthermore, the lowest grain size sample displays a Griffiths-like phase. The evidence of the emergence of this phase has been obtained from detailed dc and ac magnetization studies. We have explained our results through a phenomenological model.

Superspin relaxation in Fe3O4/hexane magnetic fluids: A dynamic susceptibility study

We have used frequency-resolved (100Hz<f<10,000Hz) ac magnetic susceptibility measurements to directly determine the Néel and Brown relaxation times in 30-nm-size Fe3O4/hexane magnetic fluids at temperatures between 200 and 300K. Our data collected on both powder and magnetic fluid samples allow the separation of the contributions from the Néel and Brown relaxation mechanisms that act concomitantly within the above-mentioned temperature range. At all temperatures we find that the Brown relaxation times (τB) are shorter than their Néel counterparts (τN), evidence that the Brown mechanism yields the major contribution towards the system’s overall superspin dynamics. τB exhibits a steep two-order-of-magnitude decrease upon heating, from τB=1×10−3s at T=237K to τB=1.5×10−5s at T=270K, a behavior mostly driven by the heating-induced reduction of the liquid carrier’s viscosity.