Ac Susceptibility Measurements Research Articles

Azido-cobalt(II) coordination polymers exhibiting slow magnetic relaxation and metamagnetic transition

Two coordination polymers of mono-dimensional doubly bridged-azido-cobalt(II) complexes catena-[Co(2,6-lutidine-N-oxide)(μ1,1-N3)2] (1) and catena-{[Co(μ1,1-N3)2(H2O)2](3-picoline-N-oxide)2} (2), where 2,6-lutidine-N-oxide = 2,6-dimethylpyridine-N-oxide and 3-picoline-N-oxide = 3-methylpyridine-N-oxide, were synthesized, and structurally characterized by single crystal X-ray crystallography. The Co(II) cations in complexes 1 and 2 are penta- and hexa-coordinate, respectively with four μ1,1-bridging azido groups and a terminal 2,6-lutidine-N-oxide molecule in 1 or two trans aqua molecules in 2. Magnetic relaxations in the zero field are consistent with single chain magnetic behavior (SCM) and the ac susceptibility measurements revealed that the weak ferromagnetic exchanges in the two complexes are associated with slow relaxation of magnetization. Complex 2 exhibits metamagnetic transition with an antiferromagnetic phase transition at 12 K at the applied field of 200 Oe.

Magnetization reversal, magnetic anisotropy and ordering studies on quenched copper-ferri-aluminates

The magnetic properties of thermally quenched spinel ferrite system, CuAlxFe2-xO4 (x = 0.0, 0.2, 0.4 and 0.6), have been investigated by means of DC magnetization, hysteresis loop characteristics and thermal variation of low field ac susceptibility measurements. The system possesses a tetragonally distorted spinel structure and exhibits a non-collinear spin arrangement. The magnetic characteristics suggest that the ferrites are low anisotropy compounds, the negative magnetization observed for x = 0.6 composition at the compensation temperature T = 22 K is due to the copper ion moment with a net effect antiparallel to that of the Fe3+ ions with different temperature dependence giving rise to a compensation effect. The low-temperature anomalies on the zero field cooled curves are due to the coexistence and interplay between the ferrimagnetic long-range ordering and short-range ordering in the system.

Spin-glass state and reversed magnetic anisotropy induced by Cr doping in the Kitaev magnet α−RuCl3

Magnetic properties of the substitution series Ru$_{1-x}$Cr$_x$Cl$_3$ were investigated to determine the evolution from the anisotropic Kitaev magnet $\alpha$-RuCl$_3$ with $J_{\rm eff} = 1/2$ magnetic Ru$^{3+}$ ions to the isotropic Heisenberg magnet CrCl$_3$ with $S = 3/2$ magnetic Cr$^{3+}$ ions. Magnetization measurements on single crystals revealed a reversal of the magnetic anisotropy under doping, which we argue to arise from the competition between anisotropic Kitaev and off-diagonal interactions on the Ru-Ru links and approximately isotropic Cr-Ru and isotropic Cr-Cr interactions. In addition, combined magnetization, ac susceptibility and specific-heat measurements clearly show the destabilization of the long-range magnetic order of $\alpha$-RuCl$_3$ in favor of a spin-glass state of Ru$_{1-x}$Cr$_x$Cl$_3$ for a low doping of $x\backsimeq0.1$. The corresponding freezing temperature as a function of Cr content shows a broad maximum around $x\backsimeq0.45$.

Magnetic Attributes of NiFe2O4 Nanoparticles: Influence of Dysprosium Ions (Dy3+) Substitution.

This paper reports the influence of dysprosium ion (Dy3+) substitution on the structural and magnetic properties of NiDyxFe2−xO4 (0.0 ≤ x ≤ 0.1) nanoparticles (NPs) prepared using a hydrothermal method. The structure and morphology of the as-synthesized NPs were characterized via X-ray diffraction (XRD), scanning and transmission electron microscope (SEM, and TEM) analyses. 57Fe Mössbauer spectra were recorded to determine the Dy3+ content dependent variation in the line width, isomer shift, quadrupole splitting, and hyperfine magnetic fields. Furthermore, the magnetic properties of the prepared NPs were also investigated by zero-field cooled (ZFC) and field cooled (FC) magnetizations and AC susceptibility measurements. The MZFC (T) results showed a blocking temperature (TB). Below TB, the products behave as ferromagnetic (FM) and act superparamagnetic (SPM) above TB. The MFC (T) curves indicated the existence of super-spin glass (SSG) behavior below Ts (spin-glass freezing temperature). The AC susceptibility measurements confirmed the existence of the two transition temperatures (i.e., TB and Ts). Numerous models, e.g., Neel–Arrhenius (N–A), Vogel–Fulcher (V–F), and critical slowing down (CSD), were used to investigate the dynamics of the systems. It was found that the Dy substitution enhanced the magnetic interactions.

A Series of Lanthanide-Based Metal-Organic Frameworks Derived from Furan-2,5-dicarboxylate and Glutarate: Structure-Corroborated Density Functional Theory Study, Magnetocaloric Effect, Slow Relaxation of Magnetization, and Luminescent Properties.

Herein, through a dual-ligand strategy, we report eight isorecticular lanthanide(III) furan-2,5-dicarboxylic acid metal-organic frameworks (Ln-MOFs) with the general formula {[Ln(2,5-FDA)0.5(Glu)(H2O)2]· xH2O} n [Ln = Sm (1), Eu (2), Gd (3), Tb (4), Dy (5), Ho (6), Er (7), and Yb (8); 2,5-FDA2- = furan-2,5-dicarboxylate and Glu2- = glutarate; x = 0.5 for 1, 2, and 4 and x = 0 for 3 and 5-8], synthesized under solvothermal conditions by using an N, N'-dimethylformamide/H2O mixed solvent system. Crystallographic data reveal that all eight Ln-MOFs 1-8 crystallize in the orthorhombic Pnma space group. All of the MOFs are isostructural as well as isomorphous with distorted monocapped square-antiprismatic geometry around the Ln1 metal center. In Ln-MOFs 1-8, the 2,5-FDA2- and Glu2- ligands exhibit μ2-κ4,η1:η1:η1:η1 and μ3-κ5,η2:η1:η1:η1 coordination modes, respectively. Topologically, assembled Ln-MOFs 1-8 consist of the 2D cem topological type. The designed Ln-MOFs 1-8 are further explored for structure-corroborated density functional theory study. Meanwhile, room temperature photoluminescence properties of Ln-MOFs 2 and 4 and magnetic properties of Ln-MOFs 3 and 5 have been explored in detail. A highly intense, ligand-sensitized, Ln3+ f-f photoluminescence emission is exhibited by Ln-MOFs 2 [Eu3+ (red emission)] and 4 [Tb3+ (green emission)]. Magnetic studies suggest weak antiferro- and ferromagnetic interactions between adjacent GdIII ions in Ln-MOF 3, thereby displaying a large magnetocaloric effect. The magnetic data measured at T = 2 K and Δ H = 30 kOe depict that the -Δ Sm value per unit mass reaches 32.1 J kg-1 K-1, which is larger than most of the GdIII-based complexes reported. The alternating-current susceptibility measurements on Ln-MOF 5 revealed that out-of-phase signals are frequency- and temperature-dependent under both 0 and 2 kOe direct-current fields, thereby suggesting a typical slow magnetic relaxation behavior with two relaxation processes. This is further supported by the Cole-Cole plots at 2.4-6 K.

Effect of process parameters on non-modulated Ni-Mn-Ga alloy manufactured using powder bed fusion

Increasingly, metal parts made by additive manufacturing are produced using powder bed fusion (PBF). In this paper we report upon the combined effects of PBF parameters, including power and scan speed, in layer-by-layer manufacturing of gas atomized non-modulated (NM) Ni-Mn-Ga alloy. The effects of process parameters upon PBF is studied by applying nine different parameter sets in the as-printed state and after homogenization and ordering. The chemical composition of the samples is analyzed using EDX attached to an SEM, and the crystal structures are determined by X-ray diffraction. The phase transformation temperatures are measured using a low-field ac susceptibility measurement system and the magnetic properties are measured with a vibrating sample magnetometer (VSM). Before the heat-treatment, all as-printed samples showed paramagnetic behavior with low magnetization and no phase transformations could be observed in the susceptibility measurements. After annealing, the samples recovered the ferromagnetic behavior with comparable magnetization to annealed gas atomized powder. The as-printed samples were composed of a mixture of different crystal structures. However, after annealing the original NM structure with a = b = 5.47 Å and c = 6.66 Å with a c/a -ratio of 1.22 was recovered and crystallographic twins could be observed in an SEM.

Extending the family of heptanuclear heterometallic Cu5Ln2 (Ln = Gd, Tb, Dy) complexes: Synthesis, crystal structures, magnetic and magnetocaloric studies

The reaction of Ln(NO3)3∙6H2O (Ln = Gd, Tb, Dy) and Cu(O2CMe)2∙H2O with the polydentate Schiff base ligands OH-C10H6-CHNC(R)(CH2OH)2 (R = CH3, H3L1; R = C2H5, H3L2) in Me2CO afforded the heptanuclear heterometallic complexes [Cu5Ln2(O2CMe)2(NO3)4(L1)2(HL1)2(Me2CO)2] (Ln = Gd (1), Tb (2), Dy (3)) and [Cu5Ln2(O2CMe)2(NO3)4(L2)2(HL2)2] (Ln = Gd (4), Tb (5), Dy (6)). Crystallographic studies revealed that complexes 1–3 and 4–6 consist of a central core {CuII5LnIII2(μ3-OR)6(μ3-O2CMe)2}8+ described as two distorted cubane subunits, {CuII3LnIII(μ3-OR)3(μ3-O2CMe)}5+, with a CuII ion in the common apex. Peripheral and bridging ligation is provided by two triply and two doubly deprotonated Schiff base ligands, two μ3-acetates and four chelating nitrates. Magnetic susceptibility measurements revealed the presence of dominant ferromagnetic interactions in all complexes. The magnetocaloric effect of 1 was examined via isothermal magnetization measurements under various applied fields and the maximum entropy change was 16.3 J kg−1 K−1 at 2 K for ΔH = 5 T. Ac susceptibility measurements of 2, 3 and 6 revealed slow magnetic relaxation processes suggesting the presence of single-molecule magnet behavior.

Coexistence of ferromagnetic and spin glass-like magnetic order in Bi10Co16O38 – Bi25FeO40 powder composite

Abstract In this article, structural and magnetic characteristics of Bi 10 Co 16 O 38 – Bi 25 FeO 40 (BCFO) sillenite composite powder prepared via hydrothermal route were explicated. Structural and microstructural details were studied using XRD and FE-SEM techniques. The magnetic ordering was probed with both static magnetization (M vs. T, M vs. H) and dynamic AC susceptibility measurements. The detailed magnetic analysis confirms the coexistence of ferromagnetic, spin-glass magnetic order below the Curie transition temperature of 227 K with a spin freezing temperature at 161 K. Critical slowing down parameter zv of 1.36 indicates mean field dependent phenomena for the observed spin glass transition temperature. Furthermore, the ferromagnetic contribution in the composite is ascribed to the low-spin state of Co 2+ ion.

Observation of spin glass behavior in chiral Mn48Fe34Si18 with a β-Mn related structure

The ternary silicide system Fe-Mn-Si exhibits several complex magnetic phases and the chemical similarity of Fe and Mn enables these two elements to be mutually substituted over a wide compositional range. Because this substitution results in chemical disorder and often causes competing magnetic exchange interactions, frustrated spin glass ordering is expected to occur for some Fe-Mn-Si phases. However, the observation of a spin glass state within these alloys has been elusive to date. This paper reports magnetization and ac susceptibility measurements on Mn48Fe34Si18. The compound crystallizes in a Mn3IrSi-type structure, which is closely related to that of β-Mn. Typical spin glass behavior is observed at low temperatures. This comprises a bifurcation of field-cooled and zero-field-cooled magnetization, a displacement of the field-cooled hysteresis loop, magnetic relaxation, a memory effect, and a sharp, frequency-dependent cusp in the ac susceptibility at the freezing temperature. Mn48Fe34Si18 is demonstrated to be a canonical spin glass.

Infiltration effects on (RE) 123 superconductors

We produced RE-123 infiltrated by Sm123 superconductors by the melt growth method. The samples have been investigated in terms of X-ray diffraction (XRD) analysis, AC susceptibility, levitation force, and a magnetic stiffness calculation. The X-ray diffraction analysis showed that the Sm123 and Y123 phases were insufficiently grown at the selected sintering temperature of 1040 °C. The transition temperature of the IP Sample is 94.28 K from the AC Susceptibility (at 1 KHz and 4 Oe applied AC field) measurement. The magnetic stiffness was calculated using our newly designed vertical magnetic levitation force measurement system. It has a Nb-Fe-B permanent magnet (∼0.5T) at 77 K with the Zero Field Cooled process. The magnetic stiffness was calculated using the data of the levitation force. The descending experimental results showed that the most significant F0was contained in the sample I5 (F0 = 9.034 N) and the largest constant b value was determined in the sample IP (b = 0.3320 mm−1). But in the ascending results, the most significant F0 is 8.604 N, and the largest constant b is 0.3047 mm−1, both calculated in the IP sample. Considering the oxygen content effects on the magnetic stiffness, one can infer that it has been positively affected by an increase in the Sm123 infiltration. These results indicatethat the produced samples could be applied to bearing systems, magnetic sensors and other technological applications.

Superconductivity in high-Tc (Tl1−xSex)Sr2CaCu2O7 system

Superconductivity up to 76 K has been achieved in Se substituted Tl-1212 phase, (Tl1−xSex)Sr2CaCu2O7. X-ray diffraction patterns showed the presence of Tl-1212 as the major phase in most samples. The highest volume fraction of Tl-1212 phase (88%) was observed in the x = 0.1 sample. The electrical resistance measurement showed the highest onset temperature, Tc−onset (76 K) for x = 0.2 and 0.4. AC susceptibility (χ = χ + iχ″) measurements showed the highest superconducting transition temperature Tcχ′ = 71 K for x = 0.4. The peak temperature, Tp of the imaginary part of the susceptibility, χ″ was also the highest for x = 0.4 sample (Tp = 69 K). The inter-grain critical current density at the peak temperature, Jc(Tp) for all samples was between 17 and 19 A cm−2. This work showed that in addition to Bi, Pb, Cr, V, Re and rare-earth elements, Se substitution for Tl also resulted in the formation of a superconducting material in the TlSr2CaCu2O7−δ phase.

Type-I superconductivity in Al6Re

While the pure elements tend to exhibit Type-I rather than Type-II superconductivity, nearly all compound superconductors are Type-II, with only a few known exceptions. We report single crystal growth and physical characterization of the rhenium aluminide Al$_6$Re, which we conclude is a Type-I superconductor based on magnetization, ac-susceptibility, and specific-heat measurements. This detection of superconductivity, despite the strong similarity of Al$_6$Re to a family of W and Mo aluminides that do not superconduct, suggests that these aluminides are an ideal testbed for identifying the relative importance of valence electron count and inversion symmetry in determining whether a material will superconduct.

Signature of Ferromagnetic Phase at Low Temperature in Low-Doped La0.88Ca0.12MnO3 Single Crystal

The confirmation of ferromagnetism at low temperature in a low-doped manganites system is always debatable. It is for the first time, electrical, magnetic, and thermal properties have been measured for manganites single crystal of La0.88Ca0.12MnO3 by using a floating-zone method. The electrical resistivity shows a perceptible change of resistance at a low temperature which can be viewed as a signature of the ferromagnetic phase. The ferromagnetic phase of the investigated La0.88Ca0.12MnO3 single crystal with Curie temperature of TC = 120 K which is in closed agreement with ac-susceptibility measurement. An analysis of the specific heat suggests the transition peak (TP) coincides with the TC and attains 1.2 J mol−1 K at 116 K. The magnetoresistance (MR) and temperature coefficient of resistance (TCR) were found to be 69% and 10% respectively, which expands its subtle potential for applications in spintronics and thermistor.

Synthesis and temperature dependent magnetic properties of nanocrystalline Ni0.5Zn0.5Fe2O4 ferrites

nanoparticles were successfully synthesized by modified citrate gel method. X-ray diffraction (XRD) analysis confirmed the development of single-phase cubic spinel structure with Fd m space group. The cation distribution was estimated by Rietveld refinement of XRD pattern and found that the prepared sample has a mixed spinel structure. The high field regions of magnetic hysteresis loops were modeled using the Law of Approach to Saturation to determine the saturation magnetization () and magnetic anisotropy constant () for the prepared nanoparticles. It is found that the values of and increases significantly with decreasing temperature. However, temperature dependence of saturation magnetization () and coercivity () were found to have considerable deviations from the Bloch’s and Kneller’s laws, respectively. This behavior is elucidated in terms of finite size effects, disordered surface spins and interparticle interactions in the prepared nanoparticles. Furthermore, the effects of interparticle interactions were investigated by using Vogel–Fulcher law for frequency dependent AC susceptibility measurements.

Observation of the topological Hall effect and signature of room-temperature antiskyrmions in Mn-Ni-Ga D2d Heusler magnets

Topologically stable nontrivial spin structures, such as skyrmions and antiskyrmions, display a large topological Hall effect owing to their quantized topological charge. Here, we present the finding of a large topological Hall effect beyond room temperature in the tetragonal phase of a Mn-Ni-Ga based ferrimagnetic Heusler shape memory alloy system. The origin of the field induced topological phase, which is also evidenced by the appearance of dips in the ac-susceptibility measurements, is attributed to the presence of magnetic antiskyrmions driven by D2d symmetry of the inverse Heusler tetragonal phase. Detailed micromagnetic simulations asserts that the antiskyrmionic phase is stabilized as a result of interplay among inhomogeneous Dzyaloshinskii-Moriya interaction, the Heisenberg exchange, and the magnetic anisotropy energy. The robustness of the present result is demonstrated by stabilizing the antiskyrmion hosting tetragonal phase up to a temperature as high as 550 K by marginally varying the chemical composition, thereby driving us a step closer to the realization of ferrimagnetic antiskyrmion based racetrack memory.

Effect of Nano-Sized Nickel Ferrite Addition on Superconducting Properties of (Tl<sub>0.85</sub>Cr<sub>0.15</sub>)Sr<sub>2</sub>CaCu<sub>2</sub>O<sub>7-δ</sub> Superconductors

The effect of nanosized nickel ferrite (NiFe2O4) addition on (Tl0.85Cr0.15)Sr2CaCu2O7-δ superconductors has been investigated. (Tl0.85Cr0.15)Sr2CaCu2O7-δ high temperature superconductors was prepared via solid-state reaction method using high purity oxide powders. Nanosized NiFe2O4 was added to the compound at composition x = 0 - 0.003 wt.%. Samples were studied using scanning electron microscopy (SEM), X-ray diffraction method (XRD), electrical resistance versus temperature, transport critical current density Jc and AC susceptibility measurements. SEM micrographs showed close-packed microstructure with low porosity. XRD patterns showed a dominant phase of Tl-1212 with a minor phase of Tl-1201 for all samples. All of the samples displayed metallic normal state behavior before the onset transition temperature (Tc-onset) which was between 102 and 104 K. The transition temperature (Tcχ’) from AC susceptibility measurement also showed the similar results between 101 and 103 K. Tc-zero was slightly suppressed with the addition of nanosized NiFe2O4. The peak temperature Tp from the imaginary part of the susceptibility χ” was found between 77 - 91 K for all samples. The highest transport critical current density (Jc) at 77 K was shown by sample x = 0.001 wt.% at 2213 mAcm-2. Nanosized NiFe2O4 has significantly enhanced the Jc of (Tl0.85Cr0.15)Sr2CaCu2O7-δ superconductor.

Effect of Different Nano-sized MgO Addition on YBa2Cu3O7-δ Superconductor

The effect of nanoparticle with different size on a superconductor is interesting because the size of the coherence length, penetration depth, and the magnetic flux in a superconductor is in the nanometer range. In this paper, we report the effects of different nano-sized MgO (20, 40, and 100 nm) addition on YBa2Cu3O7-δ(MgO)x for x = 0, 0.1, and 0.2 wt.%. X-ray diffraction patterns indicated a single YBa2Cu3O7 (YBCO) phase where the peaks were shifted to larger angles in the 20- and 40-nm MgO-added samples indicating induced stress of first order in the structure. The electrical resistance versus temperature was measured using the four-probe method. The transition temperature, Tc, for the pure YBCO showed Tc = 90 K and was suppressed to 78–80 K for the 20- and 40-nm MgO-added samples. AC susceptibility (χ = χ′ + iχ″) measurements showed a shift in the peak temperature, Tp, of the imaginary susceptibility χ″ towards lower temperatures for 20-nm MgO-added samples but increased with larger MgO (100 nm). This work showed that smaller nano-sized MgO suppressed the superconducting properties of YBCO more compared with the larger MgO.

Antiferromagnetism of β-Ce under hydrostatic pressure

The magnetic properties of β-Ce at low temperature have been studied through ac susceptibility measurements under hydrostatic He-gas pressure up to 4.5 kbar. The Néel temperature, TN = 12.7 K at 58 bar, initially increases with pressure at the rate dTN/dP = +0.32 ± 0.05 K/kbar. After releasing pressure from 4.5 to 0.06 kbar at 40 K, the magnetic susceptibility anomaly associated with the antiferromagnetic transition is markedly reduced. Surprisingly, TN also shifts from 12.7 to 14 K. Both effects likely arise from an irreversible β → α transition under pressure.

Trinuclear and Hexanuclear Lanthanide(III) Complexes of the Chiral 3+3 Macrocycle: X-ray Crystal Structures and Magnetic Properties

A new triphenolic hexaaza chiral macrocyclic amine L forms trinuclear complexes 1-3 with rare earth metal lanthanide(III) ions (Ln = Dy, Eu, and Y) with the general formula [Ln3L(μ3-OH)2(NO3)4(H2O)2]· xCH3OH. The crystal structures of the nitrate derivatives of this type reveal the presence of a {Ln3(μ3-OH)2} core within the macrocycle. For the chloride derivative of dysprosium(III) 4, a duplex of the trinuclear compound is formed to give the hexanuclear [Dy6L2(μ3-OH)3(μ3-O)(μ2-Cl)3Cl4(H2O)2] compound, in which two trinuclear macrocyclic units are linked by bridging chloride anions, supplemented by a hydrogen bond connecting the central oxo and hydroxo bridges as well as by weak interactions at the periphery of the macrocycle. The nuclear magnetic resonance spectra of these complexes reveal a dynamic behavior in solution related to exchange of axial ligands and hindered rotation of phenyl substituents. Magnetic studies of the nitrate (1-3) and chloride (4) dysprosium(III) complexes suggest the presence of weak ferromagnetic interactions between neighboring metal centers. The interaction is strongest for compound 1, and for the related duplex compound 4, it appears to be somewhat weaker. The ac susceptibility measurements for complexes 1 and 4 confirm their field-induced single-molecule magnet behavior with the following characteristics: Ueff = 10.6 cm-1 (15.2 K), τ0 = 2.05 × 10-4 s under 2500 Oe dc fields for 1; Ueff = 7.9 cm-1 (11.4 K), τ0 = 1.68 × 10-4 s under a 3000 Oe dc field for 4.

Slow Magnetic Relaxation of Co(II) Single Chains Embedded within Metal-Organic Superstructures.

Two coordination polymers of the type Co(BPDC)(N-ox), with BPDC being 4,4'-biphenyldicarboxylate and N-ox being pyridine N-oxide (PNO) or isoquinoline N-oxide (IQNO), have been synthesized and characterized. The compounds feature 2D and 3D metal-organic networks that encapsulate Co(II)-based chains in a rigid superstructure. The dc and ac magnetic properties of these Co(BPDC)(N-ox) materials have been investigated alongside those of a related Co(BDC)(PNO) compound (where BDC is 1,4-benzenedicarboxylate), which contains a smaller dicarboxylate linker. These Co(II)-containing coordination polymers exhibit slow magnetic relaxation, as observed by ac susceptibility measurements. The observed magnetic behavior of all compounds is consistent with an antiferromagnetic interaction between canted Co spins along the 1D skeleton, resulting in single-chain magnet behavior. In the case of Co(BPDC)(IQNO), weak interchain magnetic interactions yield 3D antiferromagnetic order while the inherent magnetic behavior stemming from the chain component is maintained. The combination of these effects in this material puts it at the frontier between single-chain magnets and classical bulk antiferromagnets. This work contributes to the limited group of materials featuring the organization of single-chain magnets within a coordination polymer superstructure.