Dc Magnetic Susceptibility Research Articles

Study the effect of Gd3+ incorporation into nanocrystalline (Ni–Ti) substituted Mn–Zn ferrites on its structure and functional properties

Ferrite samples with general chemical formula Mn0.9Zn0.1Ni0.05Ti0.05GdtFe1.9−tO4; (0.0≤ t≤0.05; step 0.01) were prepared using solid state reaction technique and the effect of Gd3+ ions incorporation on its physical properties has been studied. From the obtained results, XRD analysis reveals that the samples have a cubic spinel single phase structure for 0.0≤ t≤0.02; while for t≥0.03 a small peak of secondary phase (Gd3Fe5O12) appears and becomes more noticeable with increasing Gd content. The lattice parameter (a) of the prepared samples was found to be initially increases and then decreases with increasing Gd content which may be attributed to the difference in the ionic radii of the cations involved and the solubility limit of Gd3+ ions. The crystallite size of the samples was estimated using Scherrer's equation and ranged from 96nm to 107nm. A vibrating sample magnetometer (VSM) was used at room temperature in order to study the effect of Gd content on the magnetic hysteresis parameters of the prepared ferrites such as saturation magnetization and coercivity. DC molar magnetic susceptibility (χM) for the prepared samples was measured using Faraday's method as a function of temperature and the Curie temperature was calculated from the magnetic susceptibility measurements. Also the DC resistivity of the samples was measured at room temperature. The obtained results show that, the substitution by Gd3+ ions improves the electrical properties of the samples by increasing it DC electrical resistivity by 118% and consequently decreases it eddy current loss while the saturation magnetization slightly decreased by 14% only. The sample of t=0.01 shows a high dc magnetic susceptibility, high saturation magnetization (43.1emu/g), high electric resistivity 12×103Ω.m and high Curie temperature (496K), which is useful in some technological applications such as transformer and inductor cores.

New mixed-valence MnII4MnIV clusters from an unusual ligand transformation

The syntheses, crystal structures and magnetic properties are reported of two new and unusual mixed-valence Mn clusters [MnII4MnIVO(mpko)5(MeO-hmp)(mpko-hmp)(H2O)](ClO4)3 (1) and [MnII4MnIVO(ppko)5(MeO-hmp)(ppko-hmp)(H2O)](ClO4)3 (2). They were obtained from the reaction of mpkoH or ppkoH and hmpH with Mn(ClO4)2 in the presence of NaOMe, where mpkoH is methyl(pyridin-2-yl)ketone oxime, ppkoH is phenyl(pyridin-2-yl)ketone oxime, and hmpH is 2-(hydroxymethyl)pyridine. Complex 1 possesses a distorted MnII4 cubane core attached to an external MnIV by the O2− ion. The peripheral ligation includes two unprecedented hemiacetal ligands formed in situ from the reaction of hmpH with MeOH or mpkoH/ppkoH. Solid-state dc and ac magnetic susceptibility measurements established that both 1 and 2 possess an S=7/2 ground state, which was confirmed by ac in-phase susceptibility data. Simulations of the χMT versus T data established the presence of dominant antiferromagnetic exchange interactions, rationalizing the observed ground state.

Syntheses, structures, and magnetic properties of a cubane-like {Co4O4} cluster and a dinuclear CuII compound constructed from a tridentate Schiff base ligand

The employment of a tridentate Schiff base ligand, 1-(((2-hydroxy-2,3-dihydro-1H-inden-1-yl)imino)methyl)naphthalen-2-ol (H2L) in the coordination chemistry of cobalt(II) acetate and copper(II) acetate is reported. One cubane-like cluster of formula [Co4L4]·CH3OH (1·CH3OH) and one alkoxo-bridged dinuclear copper compound of composition [Cu2L2] (2) were achieved by the reactions of metal acetates with H2L under solvothermal conditions. The structures of 1·CH3OH and 2 have been established by single-crystal X-ray diffraction studies. Complex 1·CH3OH has a cubane-like {Co4O4} core with divalent metal atoms and alkoxo atoms (originated from the L2− ligands) occupying alternating vertices. The magnetic properties of 1·CH3OH and 2 have been investigated. The variable-temperature dc magnetic susceptibility studies indicate ferromagnetic CoII⋯CoII exchange interactions for 1·CH3OH and antiferromagnetic CuII⋯CuII couplings for 2. The ac magnetic susceptibility investigation reveals that complex 1·CH3OH shows the slow magnetic relaxation (SMM) behavior.

Physical properties of the candidate quantum spin-ice systemPr2Hf2O7

Physical properties of a pyrohafnate compound Pr2Hf2O7 have been investigated by ac magnetic susceptibility \chi_ ac(T), dc magnetic susceptibility \chi(T), isothermal magnetization M(H) and heat capacity C_p(T) measurements on polycrystalline as well as single crystal samples combined with high-resolution synchrotron x-ray diffraction (XRD) for structural characterization and inelastic neutron scattering (INS) to determine the crystal field energy level scheme and wave functions. Synchrotron XRD data confirm the ordered cubic pyrochlore (Fd-3m) structure without any noticeable site mixing or oxygen deficiency. No clear evidence of long range magnetic ordering is observed down to 90 mK, however the \chi_ac(T) evinces slow spin dynamics revealed by a frequency dependent broad peak associated with spin freezing. The INS data reveal the expected five well defined magnetic excitations due to crystal field splitting of the J = 4 ground state multiplet of the Pr^3+. The crystal field parameters and ground state wavefunction of Pr^3+ have been determined. The Ising anisotropic nature of magnetic ground state is inferred from the INS as well as \chi(T) and M(H) data. Together these properties make Pr2Hf2O7 a candidate compound for quantum spin-ice behavior.

Misjudging frustrations in spin liquids from oversimplified use of Curie-Weiss law

Absence of a single smoking-gun experiment to identify a quantum spin liquid, has kept their characterisation difficult till date. Featureless dc magnetic susceptibility and large antiferromagnetic frustration are always considered as the essential pointers to these systems. However, we show that the amount of frustration estimated by using generalised Curie-Weiss law on these susceptibility data are prone to errors and thus should be dealt with caution. We measure and analyse susceptibility data of Ba3ZnIr2O9, a spin orbital liquid candidate and Gd2O3, a 1.5K antiferromagnet and show the distinguishing features between them. A continuous and significant change in Curie and Weiss constants is seen to take place in Ba3ZnIr2O9 and other reported spin liquids with the change in the range of fitting temperatures showing the need of a temperature ‘range-of-fit’ analysis before commenting on the Weiss constants of spin liquids. The variation observed is similar to fluctuations among topological sectors persisting over a range of temperature in spin-ice candidates. On the other hand, even though we find correlations to exist at even 100 times the ordering temperature in Gd2O3, no such fluctuation is observed which may be used as an additional distinguishing signature of spin liquids over similarly featureless correlated paramagnets.

Magnetic Properties of CdMoO<sub>4</sub>:Dy<sup>3+</sup> Single Crystal

X-ray diffraction measurement at 298 K of CdMoO4:Dy3+ showed that the molybdenum ions are tetrahedral coordinated and Cd/Dy – dodecahedral coordinated. The Dy3+ ions are randomly distributed in the unit cell, substituting the Cd2+ ones. The temperature dependence of ac and dc magnetic susceptibility showed a lack of the Curie-Weiss behaviour and a weak response to the magnetic field. The magnetization isotherms, M(H), showed a paramagnetic-diamagnetic transition at 17 K for 〈100〉 direction and at 35 K for 〈001〉 one in the magnetic field of 70 kOe. As the temperature increased this transition was moving toward smaller magnetic fields.

Four Mixed 3d-4f 12-Metallacrown-4 Complexes: Syntheses, Structures and Magnetic Properties

The incorporation of LnIII ions into the 12-metallacrown-4 topology affords the formation of four mixed 3d-4f pentanuclear complexes of compositions [NH(C2H5)3]{[Ln(OAc)4] [12-MCMnIII(N)shi-4]}·xH2O (Ln = Sm (1), Gd (2), Tb (3), Dy (4); x = 0.5 for 1 and 3, x = 0.25 for 2, x = 0 for 4; H3shi = salicylhydroxamic acid). Compounds 1–4 were obtained from the reactions of H3shi with Mn(CH3COO)2·4H2O and Ln(NO3)3·6H2O, in the presence of N(C2H5)3. They all contain a crown-like [Mn4Ln(μ-NO)4]11+ core with four MnIII atoms being at the rim of the crown and an LnIII ion occupying the dome of the crown. The peripheral ligation about the core is provided by four η1:η1:µ acetate groups. The identity of the LnIII ions slightly affects the 12-metallacrown-4 frameworks, as demonstrated by the gradual decrease of the distances between the LnIII ions and the centres of the Mn4 planes (1.85 A for 1, 1.81 A for 2, 1.80 A for 3, and 1.77 A for 4). Variable-temperature dc magnetic susceptibility studies were carried out on polycrystalline samples of 1–4. Antiferromagnetic interactions are determined for complexes 1–4.

Magnetization, phonon, and X-ray edge absorption in barium-doped BiFeO3 ceramics

Magnetization hysteresis loops, dc and ac magnetic susceptibilities, and Raman vibrations have been characterized in (Bi1−x Ba x )FeO3−δ ceramics for x = 0.0, 0.05, 0.10, and 0.15 as functions of temperature. Ferromagnetic hysteresis loops were observed in Ba-doped compounds with increasing magnetization as Ba substitution increases. High-resolution synchrotron Fe K- and L 2,3-edge X-ray absorptions reveal an Fe3+ valence and a modification of the Fe–O–Fe bond structure by the A-site Ba substitution. The oxygen K-edge X-ray absorption suggests that the hybridization of the O 2p and Fe 3d orbitals was reduced by the Ba2+ substitution. Field-cooled and zero-field-cooled magnetic susceptibilities reveal a spin-glass behavior, which was enhanced with increasing Ba substitution. Raman vibrations of the Bi- and Fe-sensitive E(2) and A 1(1) modes reveal frequency softening and step-like anomalies in full-width-at-half-maximum in the vicinity of ~150–250 K, which were attributed to spin–phonon interaction while magnetic ordering transitions take place.

Magnetic anisotropy and superparamagnetism in La0.6Ca0.4MnO3, La0.6Sr0.4MnO3 and their mixed composition 0.875 La0.6Ca0.4MnO3/0.125 La0.6Sr0.4MnO3, agglomerated at different temperatures

The static magnetic properties of nano-particles La0.6Ca0.4MnO3 (S0C1), La0.6Sr0.4MnO3 (S1C0) and the 0.875(S0C1)0.125(S1C0) composition sintered at different temperatures, SC. 4-1 (700 °C), SC. 4-2 (900 °C), SC. 4-3 (1100 °C) and SC. 4-4 (1300 °C), have been investigated by the dc magnetic susceptibility, FC and ZFC magnetization, isothermal magnetization M(μ0H, 5 K) measurements and hysteresis loop at different temperatures. The nano-metric size of the studied compounds, determined by using the Scherrer formula and partially supported by TEM images, is at the origin of superparamagnetism phenomenon encountered in the compounds studied below the Curie temperature. The evolution of the Curie temperature is explained by the cationic disorder in A-site. To explain the difference between the theoretical and experimental values of the magnetization saturation, it has been adopted the Core-shell model.

Five Disk‐Shaped {MII7} (M = Mn, Fe, Co, Cu, Zn) Clusters and One Capsule‐Like {CuII6NaI2} Cluster Assembled from the Same Schiff Base Ligand

Six transition‐metal clusters of compositions [Mn7L6](NO3)2·2CH3OH (1), [Fe7L6](NO3)2·2CH3OH (2), [Co7L6](NO3)2·2CH3OH (3), [Cu7L6](NO3)2 (4), [Zn7L6](NO3)2·2CH3OH (5), and [Cu6Na2L6](NO3)2·4CH3OH (6) {H2L = 2‐(2‐hydroxy‐3‐methoxybenzylideneamino)phenol} have been synthesized under solvothermal conditions. The structures of 1–6 have been established based on single‐crystal X‐ray diffraction studies. Complexes 1–5 possess disk‐shaped {MII7} cores, with the central MII ion and the six peripheral MII ions being linked by six µ3‐O atoms. The six MII ions of the rim of the disk are bridged in a pairwise manner by six µ2‐O atoms. Complex 2 is a very rare example of a disk‐shaped {Fe7} cluster in which all of the Fe atoms exhibit +2 oxidation state. Furthermore, this is the first time that the five isostructural heptanuclear clusters were constructed by using an identical Schiff base ligand. The molecule of complex 6 contains a capsule‐like {Cu6Na2} core. In this core, two sodium ions reside on the two vertices of the capsule and the 12 vertices of the {Cu6O6} hexagonal prism are occupied by alternately arrayed six CuII ions and six O atoms. Photoluminescence studies suggest strong emission for 5 in the solid state at room temperature. Variable‐temperature dc magnetic susceptibility studies were carried out on polycrystalline samples of 1–4 and 6. The ac susceptibility studies were also performed with 3. Strong out‐of‐phase, χ′′, signals were observed for 3 at zero field, suggesting that 3 is a class of single molecule magnet (SMM).

Incommensurate Magnetic Structure in the Cubic Noncentrosymmetric Ternary Compound Pr5Ru3Al2

We performed magnetic susceptibility and neutron powder diffraction experiments on the ternary compound Pr5Ru3Al2. It belongs to the noncentrosymmetric and nonmirrorsymmetric cubic I213 space group. The previously reported ferromagnetic transition at 24 K was not detected in our improved quality samples. Instead, magnetic ordering was observed in the DC magnetic susceptibility at 3.8 K. Neutron powder diffraction further indicates that an incommensurate magnetic structure is established below 3.8 K, with the magnetic modulation vector (0.066, 0.066, 0.066) (r.l.u.). Using the magnetic representation analysis, we propose the block helical structure as a candidate for the incommensurate magnetic structure.

Tuning the electronic hybridization in the heavy fermion cage compound YbFe2Zn20 with Cd doping

The tuning of the electronic properties of heavy fermion compounds by chemical substitution provides excellent opportunities for further understanding the physics of hybridized ions in crystal lattices. Here we present an investigation on the effects of Cd doping in flux-grown single crystals of the complex intermetallic cage compound YbFe2Zn20, which has been described as a heavy fermion with a Sommerfeld coefficient of 535 mJ mol−1 · K−2. The substitution of Cd for Zn disturbs the system by expanding the unit cell and, in this case, the size of the Zn cages that surround the Yb and Fe. With an increasing amount of Cd, the hybridization between the Yb 4f electrons and the conduction electrons is weakened, as shown by a decrease in the Sommerfeld coefficient, which should be accompanied by a valence shift of the Yb3+ due to the negative chemical pressure effect. This scenario is also supported by the low temperature DC magnetic susceptibility, which is gradually suppressed and shows an increment of the Kondo temperature, based on a shift to higher temperatures of the characteristic broad susceptibility peak. Furthermore, the DC resistivity decreases with the isoelectronic substitution of Cd for Zn, contrary to expectations in an increasingly disordered system, and implying that the valence shift is not related to charge carrier doping. The combined results demonstrate the excellent complementarity between positive physical pressure and negative chemical pressure, and point to a rich playground for exploring the physics and chemistry of strongly correlated electron systems in the general family of Zn20 compounds, despite their structural complexity.

Crystal structure and partial Ising-like magnetic ordering of orthorhombicDy2TiO5

The structure and magnetic properties of orthorhombic $\mathrm{D}{\mathrm{y}}_{2}\mathrm{Ti}{\mathrm{O}}_{5}$ have been investigated using x-ray diffraction, neutron diffraction, and alternating current (ac)/direct current (dc) magnetic susceptibility measurements. We report a continuous structural distortion below 100 K characterized by negative thermal expansion in the [0 1 0] direction. Neutron diffraction and magnetic susceptibility measurements revealed that two-dimensional (2D) magnetic ordering begins at 3.1 K, which is followed by a three-dimensional magnetic transition at 1.7 K. The magnetic structure has been solved through a representational analysis approach and can be indexed with the propagation vector $k=[01/20]$. The spin structure corresponds to a coplanar model of interwoven 2D ``sheets'' extending in the [0 1 0] direction. The local crystal field is different for each $\mathrm{D}{\mathrm{y}}^{3+}$ ion (Dy1 and Dy2), one of which possesses strong uniaxial symmetry indicative of Ising-like magnetic ordering. Consequently, two succeeding transitions under magnetic field are observed in the ac susceptibility, which are associated with flipping each $\mathrm{D}{\mathrm{y}}^{3+}$ spin independently.

Field‐Induced Single‐Ion‐Magnetic Behavior of Octahedral CoII in a Two‐Dimensional Coordination Polymer

Two 2D coordination polymers have been synthesized by employing V‐shaped flexible terpyridine‐based ligand L [L = 4′‐(4‐methoxyphenyl)‐4,2′:6′,4′′‐terpyridine] as linker and MII (M = CoII, FeII) as nodes. Structural analysis of both complexes revealed the formation of a rare [4+4] metallocyclic unit. The extension of these cyclic units into two dimensions gives rise to an interdigitated 2D sheet structure in which the methoxy group of the ligand is oriented above and below the sheet to form crests and troughs. Detailed dc and ac magnetic susceptibility measurements revealed the field‐induced slow magnetic relaxation behavior of the magnetically isolated six‐coordinate CoII center with easy‐plane magnetic anisotropy. The effective energy barrier (Ueff) was found to be 36.9 K, which is the highest value reported so far for 2D CoII‐based single‐ion magnets.

Pressure-enhanced superconductivity in quasi-1D cobalt carbide Sc3CoC4

We have successfully synthesized the quasi-1D cobalt carbide Sc3CoC4 by using the arc-melting technique which is similar to that of the previous reports. An incomplete superconducting transition is detected at ambient pressure. In addition, two anomalies have been observed at 72 K and 143 K both from resistivity and magnetic susceptibility measurements. According to previous studies, it was argued that they correspond to the 1D Peierls-type distortion and charge-density-wave transitions, respectively. By applying a pressure, the transition at about 72 K is quickly suppressed, which is accompanied by the occurrence of a complete superconducting transition at about 4.5 K. Moreover, the DC magnetic susceptibility under high pressures also reveals the enhancement of superconductivity. We attribute this enhancement of superconductivity to the suppression of the Peierls-type distortion at about 72 K and probably together with the promoted Josephson coupling between the [CoC4]∞ one-dimensional ribbons.

Insight into the magnetism of a distorted Kagome lattice, Dy3Ru4Al12, based on polycrystalline studies

The layered compound with distorted Kagome nets, Dy3Ru4Al12, was previously reported to undergo antiferromagnetic ordering below (TN=) 7 K, based on investigations on single crystals. Here, we report the results of our investigation of AC and DC magnetic susceptibility (χ), isothermal remnant magnetization (MIRM), heat-capacity, magnetocaloric effect and magnetoresistance measurements on polycrystals. The present results reveal that there is an additional magnetic anomaly around 20 K, as though the Néel order is preceded by the formation of ferromagnetic clusters. We attribute this feature to geometric frustration of magnetism. In view of the existence of this phase, the interpretation of the linear-term in the heat-capacity in terms of spin-fluctuations from the Ru 4d band needs to be revisited. Additionally, in the vicinity of TN, AC χ shows a prominent frequency dependence and, below TN, MIRM exhibits a slow decay with time. This raises a question whether the antiferromagnetic structure in this compound is characterized by spin-glass-like dynamics. In contrast to what was reported earlier, there is a change in the sign of the magnetoresistance (MR) at the metamagnetic transition. A butter-fly-shaped (isothermal) MR loop (interestingly spanning over all the four quadrants) is observed at 2 K with distinct evidence for the magnetic phase co-existence phenomenon in zero field after travelling through metamagnetic transition field. The results on polycrystals thus provide additional information about the magnetism of this compound, revealing that the magnetism of this compound is more complex than what is believed, due to geometric frustration intrinsic to Kagome net.

Superconductivity in KCa2Fe4As4F2 with Separate Double Fe2As2 Layers.

We report the synthesis, crystal structure, and physical properties of a quinary iron arsenide fluoride, KCa2Fe4As4F2. The new compound crystallizes in a body-centered tetragonal lattice (space group I4/mmm, a = 3.8684(2) Å, c = 31.007(1) Å, Z = 2) that contains double Fe2As2 conducting layers separated by insulating Ca2F2 layers. Our measurements of electrical resistivity, direct-current magnetic susceptibility, and heat capacity demonstrate bulk superconductivity at 33 K in KCa2Fe4As4F2.

Magnetostructural Correlation for High-Nuclearity Iron(III)/Oxo Complexes and Application to Fe5, Fe6, and Fe8 Clusters.

The synthesis and characterization are reported of two new polynuclear Fe(III) complexes containing the anion of 8-hydroxyquinoline (hqnH), an N,O-chelating ligand. The complexes are [Fe8O4(O2CPh)10(hqn)4(OMe)2] (1) and [Fe6O2(OH)2(O2CPh)10(hqn)2] (2) and were obtained from reactions in MeOH (1) or H2O (2) using either low-nuclearity preformed clusters or simple metal salts as starting materials. Variable-temperature, solid-state dc and ac magnetic susceptibility studies were carried out and indicate S = 0 and S = 5 ground states for 1 and 2, respectively. In order to rationalize the ground states of these and other higher-nuclearity Fe(III)/O clusters, a magnetostructural correlation (MSC) has been developed specifically for polynuclear Fe(III)/O systems that predicts the exchange interaction constant (Jij) between two Fe(III) atoms based on the Fe-O distances and Fe-O-Fe angles at monoatomically bridging ligands. This correlation was refined using selected tri- and tetranuclear complexes in the literature for which both crystal structures and reliable experimentally determined Jij values were available. The predictive capability of the MSC was evaluated by rationalizing the ground-state spins of 1, 2, and other Fe5-Fe8 clusters, simulating the dc magnetic susceptibility data of polynuclear Fe(III) complexes, and fitting experimental dc magnetic susceptibility vs T data. The latter fits were evaluated to identify and eliminate systematic errors, and this allowed a protocol to be developed for application of this MSC to other polynuclear Fe(III)/oxo clusters.

A new family of interdimer [MnII2LnIII2]2 clusters: Syntheses, structures, and magnetic properties

A new family of isostructural Mn/Ln clusters: [MnII2LnIII2(hmp)6(NO3)4(CH3OH)2][MnII2LnIII2(hmp)6(NO3)4(H2O)2] ([Ln=Gd (1), Tb(2), Dy(3), hmpH=2-(hydroxymethyl)pyridine]) have been synthesized by the reaction of Mn(NO3)2 and Ln(NO3)3·6H2O with hmpH as ligand under solvothermal conditions. Compounds 1–3 are isostructural and possess butterfly core. That the antiferromagnetic interactions within compounds 1–3 were suggested by soild-state dc magnetic susceptibility analyses. Compound 1 displays a magnetic-caloric effect (MCE) with 21.91JKg−1K−1 of the entropy change at 5K for ΔH=8T. Compounds 2 and 3 exhibit frequency-dependent ac susceptibility signals suggestive of slow magnetic relaxation.

Spin-Driven Multiferroic Properties of PbMn7O12 Perovskite

We synthesize PbMn7O12 perovskite under high-pressure (6 GPa) and high-temperature (1373 K) conditions and investigate its structural, magnetic, dielectric, and ferroelectric properties. We find that PbMn7O12 exhibits rich physical properties from interplay among charge, orbital, and spin degrees of freedom and rich structural properties. PbMn7O12 crystallizes in space group R3̅ near room temperature and shows a structural phase transition at TCO = 397 K to a cubic structure in space group Im3̅; the Im3̅-to-R3̅ transition is associated with charge ordering. Below TOO = 294 K, a structural modulation transition associated with orbital ordering takes place. There are two magnetic transitions with Néel temperatures of TN1 = 83 K and TN2 = 77 K and probably a lock-in transition at TN3 = 43 K (on cooling). There is huge hysteresis on specific heat (between ∼37 and 65 K at 0 Oe), dielectric constant (between ∼20 and 70 K at 0 Oe), and dc and ac magnetic susceptibilities around the lock-in transition. Sharp dielectric constant, dielectric loss, and pyroelectric current anomalies are observed at TN2, indicating that electric polarization is developed at this magnetic transition, and PbMn7O12 perovskite is a spin-driven multiferroic. Polarization of PbMn7O12 is measured to be ∼4 μC/m(2). Field-induced transitions are detected at ∼63 and ∼170 kOe at 1.6-2 K; similar high-magnetic field properties are also found for CdMn7O12, CaMn7O12, and SrMn7O12. PbMn7O12 exhibits a quite small magnetodielectric effect, reaching approximately -1.3 to -1.7% at 10 K and 90 kOe.