Zero-field-cooled Research Articles

Suppression of Kondo spin-fluctuations as the origin of metamagnetic transition in the new ternary intermetallic Ce3Pd2Ge7

The metamagnetic transition in cerium-based intermetallics is a very common intriguing phenomenon that has remained the subject of close study for several decades. We report crystal structure, magnetization and resistivity of a new ternary cerium germanide Ce3Pd2Ge7 with an orthorhombic structure of La3Co2Sn7-type (space group Cmmm, cell dimensions a = 4.3257(3), b = 26.339(2), c = 4.3594(3) Å, V = 496.69(2) Å3). Low-temperature magnetic properties are characterized by a two-step metamagnetic transition, which can be associated with two nonequivalent positions of Ce ions in the lattice. The first metamagnetic transition occurs in weak magnetic fields below T1 ≈ 11 K and then moves to higher fields when the temperature goes down (B ∼ 1.5 T at T = 2 K). The second transition manifests itself below T2 ≈ 8 K as a rapid increase of magnetization, which starts from zero field and reaches saturation at fields B ≈ 0.1 T. The magnitude of each transition increases with decreasing temperature and the polarized magnetization ΔM reaches 0.13 μB/Ce and 0.08 μB/Ce upon the first and second transitions respectively. The interchange of nonmagnetic Pd and Ge ions (≈ 0.8 %) leads to the appearance of a hysteresis of metamagnetic transitions, as well as to the splitting of the field cooled (FC) and zero field cooled (ZFC) magnetization curves in hysteresis area. The dependence of the polarized magnetization ΔM on temperature which persists up to high fields as well as the continuation of the hysteresis well above the metamagnetic transition (at least up to B ∼ 9 T) indicates a new type of spin-glass-like state, which is caused by the suppression of spin fluctuations and the localization of magnetic moments during the metamagnetic transition.

Spin switching in room temperature spin reorientation transition process of Sm0.8Yb0.2FeO3 single crystal

We report that the introduction of a certain proportion of Yb ions into SmFeO3 single crystal can modulate the reduction of the spin reorientation (SR) transition temperature down to the room temperature region. Simultaneously, it maintains the spin configuration change between Γ2 (Cy, Gz, Fx) and Γ4 (Gx, Ay, Fz) and raises the magnetization compensation temperature of the single crystal. Both Zero-Field-Cooling (ZFC) and Field-Cooled-Cooling (FCC) modes along the a-axis are present with two type-I spin switching effects, which can be effectively regulated by the applied magnetic field. Interestingly, the type-II spin switching effect is observable along the c-axis in the ZFC mode under lower magnetic fields during the SR transition process at room temperature, an interesting magnetization phenomenon that is suppressed when the magnetic field is greater than 38 Oe. This type of spin switching effect arises from a partial flip of the moments of Sm3+. Additionally, the sharp spin switching induced by the magnetic field is also observed along the a- and c-axes with the variation of the magnetization with the applied magnetic field (M-H). This work is valuable for providing an insight into the magnetic coupling and competition between the two sublattices in the RFeO3 system and for facilitating the practical application of relevant spin switching materials.

Effect of ferroelectric polarization switching on the magnetization and exchange bias in BiFeO3/La2/3Sr1/3MnO3

The magnetic properties and exchange bias of the heterostructures of a ferroelectric-antiferromagnetic room-temperature multiferroic BiFeO3 (BFO) and a ferromagnetic La2/3Sr1/3MnO3 (LSMO), grown on SrTiO3 (STO) substrate using pulsed laser (PLD) deposition technique, as a function of temperature are explored. The irreversible behaviour of temperature-dependent field cooled (FC) and zero-field cooled (ZFC) magnetization curves, with blocking temperature (TB) ~250 K, and exponential decay of coercive field (HC) below TB, reveal a spin-glass like state in BFO/LSMO heterostructure. The exchange bias is observed in as-grown as well as electrically poled BFO in BFO/LSMO which diminishes above the blocking temperature. A considerable impact of electrical poling on the magnetic properties and exchange bias is noticed in the BFO/LSMO heterostructure. In the proposed model, the coupled ferroelectric/antiferromagnetic orders in BFO along with the inflection of exchange interactions between Fe3+ and Mn3+/4+ in the vicinity of the interface due to the movement of Fe3+ in BFO relative to Mn3+/4+ in LSMO during the ferroelectric polarization switching is the key factor that strongly influences the magnetic properties and exchange bias BFO/LSMO heterostructure.

Two high-spin cobalt(III) complex anions with pyridinium-based cations: synthesis, structural elucidation and magnetic properties

Two novel hybrid salts containing high spin tris(oxalato)cobaltate(III) complexes and pyridinium derivative isomer cations, viz. (C7H11N2)3[Co(C2O4)3]·nH2O (C7H11N2+ = 2-amino-4,6-dimethylpyridinium cation, n = 0 for salt 1; C7H11N2+ = 4-dimethylaminopyridinium, n = 4 for salt 2) were successfully isolated from aqueous solution. They were characterized using various physicochemical techniques, such as C, H, N microanalyses, thermogravimetric studies, FT-IR, UV-Vis, EDX, PXRD, single-crystal X-ray crystallography, and SQUID magnetometry. The size of the pyridinium derivative isomer cations has a major impact on the crystal structures. Salt 1 has a 3-D supramolecular framework formed by O–H···O hydrogen bonds between the high-spin [Co(C2O4)3]3− complex anion and the sterically encumbering 2-amino-4,6-dimethylpyridinium cations. The 3-D supramolecular framework of salt 2 is comprised of [Co(C2O4)3]3− complex anion, small size 4-dimethylaminopyridinium cations and uncoordinated water molecules via N–H···O and O–H···O hydrogen bonds. Structural cohesion is reinforced by π–π stacking interactions between the pyridine rings in both salts. Temperature-dependence magnetic moment (µ) collected under zero-field cooled (ZFC) and field-cooled (FC) conditions revealed robust antiferromagnetic ordering below TN = 25 K. The negative Weiss constant, θ = −55 K, confirmed the presence of antiferromagnetic interactions between Co(III) ions at low temperatures in 1 and the estimated effective magnetic moment of 4.5 μB supports the presence of the rare Oh high-spin Co(III) in this hybrid salt.

Effect of thickness on magnetic properties of single domain GdBCO bulk superconductors

To study the influence of thickness on the magnetic properties of ReBCO (Re = Y, Gd, Sm, Nd, etc.) bulk superconductors, a single domain gadolinium barium copper oxide (GdBCO) bulk superconductor fabricated by the Re + 011 top seeded infiltration growth (Re + 011 TSIG) method was continuously sliced along the bottom to obtain samples of different thickness. The levitation force and attractive force of these samples were tested at 77 K in the zero-field-cooled (ZFC) state. It is found that as the sample thickness decreases, the levitation force decreases gradually whereas the attractive force increases. This is related to the varied ability to resist the penetration of magnetic field occasioned by varying sample thickness, which are deeply revealed by combining with the characteristics of the non-ideal type-II superconductor. Further, the levitation force exhibits a trend of slow initial change followed by rapid change, which may be attributed to the growth of the sample. Measurement of the trapped field shows that a similar distribution of trapped field at the top and bottom surfaces can be achieved by removing some materials from the bottom of the bulk. These results provide a reference for meeting the actual requirements of ReBCO bulks of different thicknesses and greatly contribute to practical designs and applications.

Ligand Modified and Light Switched On/Off Single-Chain Magnets of {Fe 2 Co} Coordination Polymers via Metal-to-Metal Charge Transfer

Ligand Modified and Light Switched On/Off Single-Chain Magnets of {Fe ₂ Co} Coordination Polymers via Metal-to-Metal Charge Transfer

Effect of Sn substitution at Sb site on the magnetic properties of Mn2NiSb full-Heusler alloy

Alignment of spin of Mn-Mn atoms in Heusler structure mainly depends upon the distance between them which can be easily manipulated by substituting the main group Z-elements in the Mn2-based full-Heusler alloys. In this article, we report the effect of Sn doping at the Sb site in the Mn2NiSb1−XSnX (0.02≤x≤0.1) full-Heusler alloys. We have performed the X-Ray diffraction (XRD) measurement of each sample to obtain the structural information of the synthesized full-Heusler phase. Rietveld refinement performed on the each XRD data of Mn2NiSb1−XSnX (0.02≤x≤0.1) revealed that all the samples were crystallized in the Hg2CuTi prototype (Space group-Fm3m) structure. Analysis of selected area diffraction (SAED) pattern obtained from transmission electron microscopy (TEM) measurement revealed that a single phase of full-Heusler was obtained for the highest Sn content (x = 0.1) sample. Magnetization variation with applied magnetic field plot exhibited the ferromagnetic ground state of each sample as evidenced from hysteresis loop and saturation was obtained up to 1.0 Tesla field. Zero field cooled (ZFC) and field cooled (FC) measurements were also investigated and splitting between ZFC and FC were found to be increasing with an increase in the Sn content. This increment in ZFC and FC splitting with Sn content was attributed to the coupling between the ferrimagnetic (FIM) nature of Mn2NiSn phase with ferromagnetic (FM) nature of Mn2NiSb phase at the interfaces. Small shifting of hysteresis curve observed in the virgin M-H loop around the origin also indicated the spontaneous exchange biasing due to the FM/FIM interaction. Compensation of magnetization followed by exchange biasing with two magnetic phase (FM/FIM) governed by the controlled doping of Sn in Mn2NiSb have been alluringly elaborated. Direct interaction between different known magnetic phases/sub-lattices are rarely investigated which can be used to make suitable materials for spintronic application such as magneto resistive read heads and sensors.

Equivalent Models of Critical Current and Magnetization for Calculating the Magnetic Field in Simply Connected Structures Made of HTS Bulk and HTS Tape

This paper proposes a way to represent the anisotropic nonlinear superconducting properties using a discrete model for magnetization with the corresponding critical parameters, equivalent to the Power Law model for currents. This simplified model makes it possible to analyze magnetic systems with superconducting elements in a stationary mode, which reduces the calculation time. Using of proposed model is demonstrated by the calculation of force interactions between high-temperature superconducting (HTS) samples and permanent magnet in zero-field-cooling (ZFC) and field-cooling (FC) modes. HTS bulks in the form of a prism and stack made of HTS tape are considered. The calculation of the electromagnetic field was carried out using the method of integral equations for field sources. The data of calculations are compared with the results of experimental studies.

Pressure-Induced Intermetallic Charge Transfer and Semiconductor-Metal Transition in Two-Dimensional AgRuO 3

Pressure-Induced Intermetallic Charge Transfer and Semiconductor-Metal Transition in Two-Dimensional AgRuO ₃

Successive weak-ferromagnetic transitions in α-Sm2S3

Magnetization and specific heat have been investigated for a single crystal and a sintered sample of α-Sm2S3 having an orthorhombic crystal structure. The weak-ferromagnetic transitions have been found and the Curie temperatures are determined as TC1 = 3.6 K and TC2 = 1.8 K from the magnetic specific heat Cmag(T) of a single crystal under no magnetic field. The weak-ferromagnetic features are extremely anisotropic, and the easy-magnetization axis is c which is perpendicular to the longitudinal direction of the needle-like single crystal. The saturation magnetization at T = 2.0 K and H = 100 Oe along the c-axis after field-cooling (FC) is so small as 1/18 of the full moment of Sm3+. The magnetization M(T) after zero-field cooling (ZFC) shows a curious peak at about 4.5 K just above TC1 regardless of the direction of the applied magnetic field for the single crystal. While both M(T) curves of FC/ZFC for the sintered sample show such peaks at about 4.0 K. The Cmag(T) behaves characteristically depending on the direction of the applied magnetic field. The magnetic entropy Smag(T) is also extremely anisotropic for the magnetic-field direction, and the Smag(T) under H//a is almost invariant to the field within 70 kOe. Therefore, it might be useable for controlling MCE effect by its rotating in magnetic field.

Magnetic properties and exchange bias in BiFeO3/La2/3Sr1/3MnO3 heterostructure

A sizable exchange bias (HEB∼30Oe at 10 K) in the magnetic hysteresis of BiFeO3/La2/3Sr1/3MnO3 heterostructure is observed under the cooling field (±3 kOe) applied perpendicular to the surface of the films. The exchange bias field (HEB) decreases with increasing temperature and becomes zero above 200 K. The temperature-dependent field cooled (FC) and zero-field cooled (ZFC) magnetization curves show irreversible behaviour, with a blocking temperature (TB) ∼225 K. The coercive field of the hysteresis loop, below the blocking temperature, decays exponentially with increasing temperature. These magnetic characteristics of BiFeO3/La2/3Sr1/3MnO3 heterostructure point towards a possibility of a spin-glass-like state due to the magnetic exchange interactions between the magnetic ions of both the layers in the vicinity of the interface, leading to complex magnetic structure. The sizable exchange bias observed below the blocking temperature is most likely originated from the exchange coupling between the magnetic ions at the interface.

Chiriality in a Three-band Superconducting Prism in ZFC and FC Processes

In the present work, we will study the superconducting properties of a mesoscopic three-dimensional prism with square transversal section under an external magnetic field in both Zero-Field Cooling (ZFC) and Field-Cooling (FC) process. The studied sample is a three-band system (with three condensates \(\psi _{1}\), \(\psi _{2}\), \(\psi _{3}\)), in which we take a Josephson type inter-band coupling simulated via \(\gamma\) parameter. We analyze the magnetization, superconducting electronic density and free Gibbs energy considering both processes. As results, we found an interesting tunneling of vortex and anti-vortex between the bands, and vortex cluster configuration in the sample. This behaviour is due to the non-monotonic interaction between the bands.

Spin-glass-like behavior in SmFeAsO0.8F0.2

The iron-based oxypnictide superconductor SmFeAsO0.8F0.2 was synthesized under high pressure and investigated by measuring the dc magnetic susceptibility. The zero-field cooled (ZFC) magnetic susceptibility confirmed the bulk superconductivity of the sample with a critical temperature Tc ≈ 50 K and a significant jump in magnetization at ∼4.3 K, usually attributed to the antiferromagnetic ordering of Sm3+ ions in this system. Since the occurrence of the jump depends on the cooling history, our data strongly suggest a spin-glass-like behavior.

Local Atomic Order, Morphology, and Magnetic Properties in Silica‐Coated FeCo Nanoparticles Synthesized by Coprecipitation Technique

Nanoparticles (NPs) of pure Fe25Co75 are sintered by Fe and Co coprecipitation followed by SiO2 deposition by tetraethoxysilane hydrolysis to form silica‐coated Fe25Co75 NPs ((Fe25Co75)x(SiO2)100–x (90 ≤ x ≤ 10, wt%)). Study of the morphology and phase composition of (Fe25Co75)x(SiO2)100–x nanopowders evidences the formation of agglomerations of NPs with individual medium diameter ≈20–50 nm containing partially oxidized cores of α‐FeCo bcc alloy covered with amorphous SiO2. Mössbauer spectroscopy clearly reveals that coverage with SiO2 shells promotes up to four‐time enhancement of resistance of FeCo cores to undesirable formation of surface Fe(Co) hydroxides. Temperature dependencies of magnetization recorded under field‐cooled (FC) and zero‐field‐cooled (ZFC) protocols for uncoated Fe25Co75 and (Fe25Co75)70(SiO2)30 nanopowders reveal that some part of NPs being in single‐domain state form superferromagnetic long‐range ordering.

The study of superconducting and magnetic properties of bis oxalate (C22H22O6) added bulk MgB2

The effect of bis oxalate (C22H22O6) addition on critical current density (Jc), lattice parameters, microstructure, superconducting temperature (Tc), magnetic levitation force (Fz) and lateral force (Fx) properties of bulk MgB2 has been studied for the first time in this study. Bulk MgB2 samples containing × wt% C22H22O6 (x ranging from 0, 1.5, 3, 4.5, 6 and 9 wt%) were fabricated with by in-situ solid state sintering technique at 775 °C. Fz and Fx measurements at 25 K and 30 K were made under zero-field-cooled (ZFC) and field- cooled (FC) regimes. The analysis of XRD and SEM points out a drop in lattice parameters and grain size of bis oxalate added samples and endorses C replacement in B sites in MgB2 lattice. It was observed that the bis oxalate addition has a progressive effect on magnetic levitation performance of MgB2. Whereas the maximum Fz and Fx values of undoped sample show 16.91 N and 7.10 N at 25 K, the maximum force values of the 3 wt% (BO) added sample correspond to 18.62 N and 8.49 N at 25 K. Furthermore, the (BO) addition meaningfully rises the critical current density (Jc) values of MgB2. The Jc values observed as 57 kA/cm2 and 70 kA/cm2 in self-field at 25 K for pure and 3 wt% (BO) doped MgB2 sample. The experimental results reveal that C22H22O6, as an example of carbohydrate, is an effective C-containing additive for the enhancement of the superconducting and magnetic levitation capacities of MgB2.

Insights into the honeycomb ordered Li3(MnM)SbO6 (M(II) = Co, Ni, Zn, Mg) and Li3(CoMʹ)SbO6 (Mʹ(II) = Ni, Zn, Mg) oxides

The present study deals with the designing of new honeycomb layered oxides, Li3(MnM)SbO6 (M(II) = Co, Ni, Zn, Mg) and Li3(CoMʹ)SbO6 (Mʹ(II) = Ni, Zn, Mg) belonging to the monoclinic (S. G. C2/m) layered structural family. A cationic mixing of Li+ and Mn2+ is expected for the solid solution members, Li3(MnM)SbO6 (M(II) = Co, Ni, Zn, Mg) similar to Li3Mn2SbO6. Li3(CoMʹ)SbO6 (Mʹ(II) = Ni, Zn, Mg) oxides also synthesized through high temperature solid state methods, adopt monoclinic (S. G. C2/m) structures as confirmed by the profile fitting of the PXRD measurements. Notably, the formation of Li3(MnMg)SbO6 and Li3(CoMg)SbO6 is worth highlighting since Li3Mg2SbO6 and Li3Co2SbO6 are known in thermodynamically stable orthorhombic (S. G. Fddd) rock salt superstructures. Variable temperature magnetic susceptibility measurements of the Mn2+ based oxides register an antiferromagnetic (AFM) ordering at low temperatures (<20 K) except Li3(MnZn)SbO6 and Li3(MnMg)SbO6. In addition, the divergence (∼40–60 K) between ZFC (Zero Field Cooled) and FC (Field Cooled) data appearing in Li3(MnCo)SbO6, Li3(MnNi)SbO6, and Li3(MnMg)SbO6 indicate the possible impurity of Mn3O4. Isothermal magnetization measurements at 300 K confirm typical paramagnetic behavior and a non-linear behavior at 2 K, suggesting the presence of competing ferromagnetic interactions. All the members of the series, Li3(CoMʹ)SbO6 (Mʹ(II) = Ni, Zn, Mg), exhibit clear AFM transition below 15 K. Isothermal magnetization measurements for Li3(CoNi)SbO6 shows sign of spin-flop transition at magnetic field 2.1 T similar to Li3Co2SbO6. In comparison, Li3(CoZn)SbO6 and Li3(CoMg)SbO6 only show a sigmoidal curve at 2 K. Optical property measurements revealed the transitions arising from the presence of the (MnM)2+ and (CoMʹ)2+ cations.

Magnetic and electrical transport studies of polycrystalline Sr1− x Bi x Fe12O19 (x = 0, 0.01, and 0.02)

Bismuth-substituted strontium hexaferrites, Sr1−x Bi x Fe12O19 for x = 0, 0.01 and 0.02, are studied via powder neutron diffraction (ND), magnetization (M) studies, Mössbauer spectroscopy, and electrical transport. ND results show an indication of increasing Fe2+ at 12k crystallographic sites (which is supported by Mössbauer results), with increasing Bi in the sample. They also suggest an increase in strain due to Bi substitution for the polyhedral associated with 2a and 2b spin-up and 4f1 spin-down sites. The M measurements over a wide temperature range (3–823 K), shows irreversibility in zero field cooled (ZFC) and field cooled data right below the Curie temperature, along with the Hopkinson peak in the ZFC data. The temperature dependence of saturated magnetization follows the Bloch relation but that of the coercive field shows unconventional behavior. The coercive field data is fitted using an equation devised by taking into consideration of all the three anisotropies. The critical exponents at the ferromagnetic–paramagnetic phase transition boundary, calculated using modified Arrott plots, are slightly overvalued as per mean-field theory. The temperature dependence of resistivity displays nearest-neighbor hopping conduction in all the three samples. The conductivity increases with increasing Bi in the sample, due to the increasing Fe2+ content, which facilitates the electron hopping between Fe sites. The magnetoresistance measured at various sub-room temperatures for all the compounds shows the interplay of anisotropy magnetoresistance (AMR) and giant magnetoresistance (GMR). Low temperature data are dominated by GMR and gradual participation of AMR increases as room temperature is approached.

Flexomagnetic effects on inhomogeneously strained multiferroics composites

Herein, the origin of flexomagnetic effect in Pb[(Zr0.52Ti0.48)0.60(Fe0.67W0.33)0.40]O3]0.80-[CoFe2O4]0.20 (PZTFW–CFO) multiferroic composite is demonstrated. An external inhomogeneous strain on thick composite films significantly changes the crystal lattice constants and phonon wave numbers related to single-phase PZTFW and CFO ceramics. Surface morphology indicates that inhomogeneous strain modified the magnetic dipole moments that partly regain their original position after removing external inhomogeneous strain. The magnitude of magnetic susceptibility increased under inhomogeneous strain for a small probe of the magnetic field. The magnetic anisotropic energy (MAE) supports that under-applied inhomogeneous strain reduces surface spin disorders and is responsible for the enhancement of zero field cooled (ZFC) and field cooled (FC) magnetization. Under a high external magnetic field (>100 Oe), it would be hard to detect the weak flexomagnetic effects. This work provides a framework for the effect of macroscopic inhomogeneous strain gradient on magnetic moments in multiferroics composites suggesting its suitability for the sensors and actuators applications.

Creep effects on the Campbell response in type-II superconductors

Applying the strong pinning formalism to the mixed state of a type II superconductor, we study the effect of thermal fluctuations (or creep) on the penetration of an ac magnetic field as quantified by the so-called Campbell length $\lambda_\textrm{C}$. Within strong pinning theory, vortices get pinned by individual defects, with the jumps in the pinning energy ($\Delta e_\mathrm{pin}$) and force ($\Delta f_\mathrm{pin}$) between bistable pinned and free states quantifying the pinning process. We find that the evolution of the Campbell length $\lambda_{\rm C}(t)$ as a function of time $t$ is the result of two competing effects, the change in the force jumps $\Delta f_\mathrm{pin}(t)$ and a change in the trapping area $S_\mathrm{trap}(t)$ of vortices; the latter describes the area around the defect where a nearby vortex gets and remains trapped. Contrary to naive expectation, we find that during the decay of the critical state in a zero-field cooled (ZFC) experiment, the Campbell length $\lambda_{\rm C}(t)$ is usually nonmonotonic, first decreasing with time $t$ and then increasing for long waiting times. Field cooled (FC) experiments exhibit hysteretic effects in $\lambda_\textrm{C}$; relaxation then turns out to be predominantly monotonic, but its magnitude and direction depends on the specific phase of the cooling--heating cycle. Furthermore, when approaching equilibrium, the Campbell length relaxes to a finite value, different from the persistent current which vanishes at long waiting times $t$, e.g., above the irreversibility line. Finally, measuring the Campbell length $\lambda_\textrm{C}(t)$ for different states, zero-field cooled, field cooled, and relaxed, as a function of different waiting times $t$ and temperatures $T,$ allows to spectroscopyse the pinning potential of the defects.

Effect of chromium substitution on the electrical and magnetic properties of multiferroic yttrium manganite

Yttrium Manganite is a multiferroic material and has potential applications in Ferroelectric Random Access Memories. Chromium is substituted with a view to enhancing the electrical conductivity. Compositions belonging to the series Y1−xCrxMnO3, (x = 0, 0.05, 0.1, and 0.3) were synthesized by employing a citrate gel method. Pre characterized samples using X-ray diffraction and Scanning Electron Microscopy were then subjected to impedance spectroscopy to understand the conduction mechanism vis-à-vis small polaron hopping or variable range hopping. Cole-Cole and Nyquist plots were utilized to arrive at the equivalent circuit. Ferroelectric measurements were carried out to understand the polarization mechanisms. Magnetic measurements were also conducted to observe the change in magnetic properties with Chromium substitution. Field Cooled (FC) and Zero Field Cooled (ZFC) magnetization measurements revealed the presence of ferromagnetic clusters in an antiferromagnetic matrix. It has been found that Chromium substitution enhances the electrical conductivity while it diminishes the ferroelectric properties.