Effective Magnetic Moment Research Articles

Electrical, Dielectric, and Magnetic Characteristics of (BiBa)(FeMn2)O8

A new compound of chemical formula (BiBa)(FeMn2)O8 is prepared by a solid‐state reaction method. X‐ray structural studies confirm orthorhombic unit cell of the compound. Room‐temperature magnetic data display ferromagnetic hysteresis loop with high value of effective magnetic moments. The dependence of dielectric constant, loss tangent, impedance, and the conductivity at different frequencies (1 kHz−1 MHz) are measured using LCR meter on rise of temperature from room temperature to 500 °C. The dielectric constant increases on rise of temperature due to Maxell–Wagner polarization, and the loss tangent displays similar behavior. A low value of loss tangent is obtained at higher frequencies, which paves the way for the application of the compound in high‐frequency devices. The real impedance of the compound decreases indicating NTCR (negative temperature coefficient of resistance) behavior, and the imaginary impedance displays relaxor behavior. The Nyquist plot fits to a series combination of two RQC circuits ((RQC)(RQC)) and indicates the presence of non‐Debye relaxation. The frequency variation of conductivity obeys Jonscher's power law and reveals different conduction mechanisms in grain and grain boundary regions.

Synthesis, spectroscopic determination and in vitro antimicrobial studies of cobalt(ii) and nickel(ii) complexes of a Schiff base derived from 1h-indole-2,3- dione with hydrazinecarbothioamide

Condensation of H-Indole-2,3-dione with Hydrazinecarbothioamide produced a Schiff base (2Z)-2-(2-Hydroxy-3H-indol-3- ylidinehydrzinE- 1-Carbothioamide. Cobalt(II) and Nickel(II) complexes, were prepared by the interaction of the metal(II) salts with the synthesized Schiff base. The prepared compounds were analysed by magnetic susceptibility, molar conductance, FTIR, AAS, solubility absorbance and empirical formula. The complexes showed moderate values of decomposition temperatures. Infrared spectral data of the Schiff base and the complexes, indicated coordination of the Schiff base to the metal(II) ions via azomethine nitrogen, indole oxygen and thione sulphur. The effective magnetic moment of the complexes suggested an octahedral geometry. The molar conductivities indicated a non- electrolytic nature of these complexes. The results of the absorbance and the empirical formula showed that, the Schiff base is monobasic and tridentate in nature towards the metal ions. Both the ligand and the complexes were screened for antimicrobial activity against Staphylococcus aureus, Salmonella typhimurium, Escherichia coli (bacteria); Aspergillus flavus, Aspergillus fumigatus and Mucor (indicus species) (fungi). Amoxicillin and Ketoconazole were used as positive control for the bacteria and fungi isolates respectively. The results showed that the complexes are more active than the free ligand but less active when compared with the standards.

Cr(II) and Cr(III) NCN pincer complexes: synthesis, structure, and catalytic reactivity

The synthesis, characterization, and reactivity of several new Cr(II) and Cr(III) complexes featuring an NCN pincer ligand with an arene backbone connected to amine donors NEt2 and NiPr2 via CH2-linkers is described. Reacting the in situ lithiated ligand precursor N(C–Br)NCH2-Et with [CrCl3(THF)3] resulted in the formation of the Cr(III) complex trans-[Cr(κ3NCN-NCNCH2-Et)(Cl)2(THF)]. Upon reaction of lithiated N(C–Br)NCH2-iPr with a suspension of anhydrous CrCl2, the Cr(II) complex [Cr(κ2NC-NCNCH2-iPr)2] is formed featuring two NCN ligands bound in κ2NC-fashion. In contrast, when lithiated N(C–Br)NCH2-iPr is reacted with a homogeneous solution of anhydrous CrX2 (X = Cl, Br), complexes [Cr(κ3NCN-NCNCH2-iPr)X] are obtained. Treatment of [Cr(κ3NCN-NCNCH2-iPr)Cl] with 1 equiv of PhCH2MgCl and LiCH2SiMe3 afforded the alkyl complexes [Cr(κ3NCN-NCNCH2-iPr)(CH2Ph)] and [Cr(κ3NCN-NCNCH2-iPr)(CH2SiMe3)]. All Cr(II) complexes exhibit effective magnetic moments in the range of 4.7–4.9 µB which is indicative for d4 high spin systems. If a solution of lithiated N(C–Br)NCH2-iPr is treated with CrCl2, followed by addition of an excess of Na[HB(Et)3], the dimeric complex [Cr(κ2NC-NCNCH2-iPr)(μ2-H)]2 is obtained bearing two bridging hydride ligands. [Cr(κ3NCN-NCNCH2-iPr)(CH2SiMe3)] turned out to be catalytically active for the hydrosilylation of ketones at room temperature with a catalyst loading of 1 mol%. X-ray structures of all complexes are presented.Graphical abstract

Improved magnetic properties of Fe substituted La2CoMnO6 for spintronic applications

A detailed study of magnetic behaviour of double perovskites was carried out by developing La2Co1-xFexMnO6; (x = 0.0, 0.2, 0.5, 0.8 and 1.0) via sol–gel technique. All samples showed single magnetic transition except pure LCMO (x = 0.0) and LCFMO2 (x = 0.5). Temperature dependent inverse magnetic susceptibility (χ-1) was fitted in accordance with Curie-Weiss law. μeff (effective magnetic moment) was determined for all the developed samples. Pure LCMO showed a downward divergence from Curie-Weiss law below 230 K but above transition temperature which indicates the characteristics of Griffiths phase. Saturation magnetization (Ms) increased initially and then decreased, whereas coercive field (Hc) was found to be monotonous decreased with increase in Fe content. LCFMO1 (x = 0.2) was noticed to have maximum Ms (38.87 emu/g) which indicated that the magnetic properties of pure LCMO were improved with Fe substitution, but for lower substitution only. Magnetization vs. field (M−H) curves were not well saturated even at a magnetic field of 60 kOe, therefore, values of Ms for all the samples were estimated using law of approach to saturation. With increase in Fe content, an increased anti-site disorder among Mn and Co strengthened antiferromagnetic (AFM) super exchange interactions and weakened ferromagnetism (FM). Therefore, substitution of Fe on Co-site was responsible for systematic decrease in saturation magnetization when × exceeded 0.2.

Comparison of Magnetic Deflection among Neutral Sodium-Doped Clusters: Na(H2O)n, Na(NH3)n, Na(MeOH)n, and Na(DME)n.

Using a pulsed Stern-Gerlach deflection experiment, we present the results of a comparative study on the magnetic properties of neutral sodium-doped solvent clusters Na(Sol)n with n = 1-4 (Sol: H2O, NH3, CH3OH, CH3OCH3). Experimental deflection ratios are compared with values calculated from molecular dynamics simulations. NaNH3 and NaH2O are deflected as a spin 1/2 system, consistent with spin transitions occurring on a time scale significantly longer than 100 μs. For all other clusters, reduced deflection is observed. The observed magnetic deflection behavior is correlated to the number of thermally populated rotational states in the clusters. We discuss that spin-rotational couplings allow for avoided crossings and a reduction in the effective magnetic moment of the cluster. This work attempts to understand the evolution of magnetic properties in isolated weakly bound clusters and is relevant to diamagnetic and paramagnetic species expected to exist in solvated electron systems.

Highly efficient lead removal from water by Nd0.90Ho0.10FeO3 nanoparticles and studying their optical and magnetic properties

Ho-doped NdFeO3 was synthesized using the citrate method. The X-ray diffraction (XRD) illustrated that Nd0.90Ho0.10FeO3 was crystalline at the nanoscale, with a crystallite size of 39.136 nm. The field emission scanning electron microscope (FESEM) illustrated the porous nature of Nd0.90Ho0.10FeO3, which increases the active sites to absorb the heavy metals on the sample surface. Energy-dispersive X-ray (EDX) data assures the prepared sample has the chemical formula Nd0.90Ho0.10FeO3. The magnetic properties of Nd0.90Ho0.10FeO3 were determined using the magnetization hysteresis loop and Faraday’s method. Many magnetic parameters of the sample have been discussed, such as the coercive field, the exchange bias (Hex), and the switching field distribution (SFD). Ho-doped NdFeO3 has an antiferromagnetic (AFM) character with an effective magnetic moment of 3.903 B.M. The UV–visible light absorbance of Nd0.90Ho0.10FeO3 is due to the transfer of electrons from the oxygen 2p state to the iron 3d state. Nd0.90Ho0.10FeO3 nanoparticles have an optical direct transition with an energy gap Eg = 1.106 eV. Ho-doped NdFeO3 can adsorb many heavy metals (Co2+, Ni2+, Pb2+, Cr6+, and Cd2+) from water. The removal efficiency is high for Pb2+ ions, which equals 72.39%. The Langmuir isotherm mode is the best-fit model for adsorbing the Pb2+ ions from water.

Magnetic Behavior of Light Lanthanide (La–Tb) in Linear‐Chain Nitrilo‐Tris‐Methylenephosphonates with Different Structures

The magnetic susceptibility is measured for two series of linear organic–inorganic coordination polymers I‐Ln and II‐Ln (Ln = La–Tb). The structure of the polymers (isostructural in each series I‐Ln and II‐Ln) differs in the length and structure of the bridges and in the nearest environment of the lanthanides. The effective magnetic moments of lanthanide atoms are determined from the magnetic susceptibility. The measured magnetic moments agree with the values characteristic of isolated trivalent 3+ ions for all cases, except for Tb which demonstrates a higher value of 12.25 μB in one of the complexes. An analysis of the X‐ray photoelectron spectrum of Tb 5s makes it possible to estimate the spin magnetic moment of the Tb ion.

Soft scattering evaporation of dark matter subhalos by inner galactic gases

The large gap between a galactic dark matter subhalo’s velocity and its own gravitational binding velocity creates the situation that small subhalos can be evaporated before dark matter thermalize with baryons due to the low binding velocity. In case dark matter acquires an electromagnetic dipole moment, the survival of low-mass subhalos requires stringent limits on the photon-mediated soft scattering. The current stringent direct detection limits indicate for a small dipole moment, which lets DM decouple early and allows small subhalos to form. We calculate the DM kinetic decoupling temperature in the Early Universe and evaluate the smallest protohalo mass. In the late Universe, low-mass subhalos can be evaporated via soft collision by ionized gas and accelerated cosmic rays. We calculate the subhalos evaporation rate and show that subhalos lighter than 10^{-5}M_{odot } in the gaseous inner galactic region are subject to evaporation via dark matter’s effective electric and magnetic dipole moments below current direct detection limits, which potentially affects the low-mass subhalos distribution in the galactic center.

Peculiar crystal structure and long-range order of spin-1/2 ladders in MoOBr3

Tetragonal crystal structure of molybdenum oxytribromide, MoOBr3, consists of non-planar Mo2Br6 units joined by non-equidistant Mo-O-Mo bonds into infinite ladders, which are connected to each other by the van der Waals forces. Within unit cell, the apical Mo atoms in any given ladder are shifted along the c axis either above (+z) or below (−z) the basal ab plane of the Br atoms. Magnetic susceptibility taken at various frequencies χac(T) and magnetic fields χdc(T) as well as specific heat Cp(T) data evidence the formation of a long-range antiferromagnetic order at TN = 34 ± 1 K with largely reduced effective magnetic moments µeff = 1.3 ± 0.1 µB. First principles GGA+U calculations point to the predominance of intra-ladder ferromagnetic exchange interaction on both rungs Jrung = − 10 meV and legs Jleg = − 1 meV of the ladder, while much weaker inter-ladder antiferromagnetic exchange interaction Jinter = 0.2 meV couples the ladders. The anisotropic part of the exchange K = 0.6 meV in combination with Jinter allows estimating the spin-flop transition field µ0Hspin-flop ∼ 6 T in good correspondence with the magnetization M(H) data.

Large magnetocaloric effect and magnetic properties of EuRhO3

We report on the structural, magnetic, and magnetocaloric properties of EuRhO3 powders. The oxidation states of Eu and Rh ions were studied using X-ray photoelectron spectroscopy (XPS). It is found that the Eu ions are mainly in the divalent oxidation state while the Rh ions have +4 state. EuRhO3 powders are found to be antiferromagnetic with a second order magnetic transition at Néel temperature (TN = 2.9 K). Analysis of the magnetic susceptibility versus temperature data in terms of the Curie–Weiss law: (χ = C/(T–θW)) for T > TN, yields θW = −3.1 K and effective magnetic moment μeffexp = 7.72 μB, which is close to the theoretical value μefftheo = 7.94 μB. The magnetic entropy change (–ΔSM), was determined by employing the thermodynamic Maxwell's relation. At μ0H = 5 T and near TN, (–ΔSMMax) and relative cooling power (RCP) exhibit large values of 33.7 J/(kg⋅K) and 238 J/kg, respectively. The large magnitude of –ΔSM and RCP show that the EuRhO3 compound could be a potential candidate to be used in cryogenic magnetic refrigeration.

Synthesis, structural, impedance, optical, Mössbauer characterizations and magnetic studies of Pb-containing germanate compounds

The orthorhombic antiferromagnetic germanate minerals Pb2Fe2Ge2O9 and Pb2Mn2Ge2O9 have been prepared via solid state reaction procedure. An extensive study of structural, dielectric, optical and magnetic properties of both the germanates have been investigated by employing different measurements such as X-ray diffraction, FTIR, SEM, impedance, UV–Vis–NIR & Mössbauer spectroscopic and magnetometary. Rietveld refinement of room temperature XRD patterns revealed that both the compounds crystallize in the orthorhombic space group Pbcn. FTIR spectrum exhibits the presence of M−O & Ge–O bonds which confirms strong chemical bonding. Morphological analysis through SEM showed good crystallinity of both the samples. The variation of dielectric constant, loss tangent and impedance with frequency have been studied and it has been established that both the germanates are semiconducting at 300K (RT) which may be attributed to the stacking of ions at grain boundaries. The optical band gaps estimated by UV–Vis–NIR spectroscopic measurements further confirms the semiconducting nature of the prepared germanates. 57Fe Mössbauer spectroscopic measurement on synthesized Pb2Fe2Ge2O9 sample was carried out at RT. The obtained values of IS and QS showed that iron is in Fe3+ high spin state (t2g3eg2,s=5/2) and occupy two different sites, Fe1 and Fe2. The field dependent magnetization measurements show that both the compounds display dominant paramagnetic nature at 300K. The temperature dependent magnetization data reveal very sharp first order type AFM to PM transition at TN ∼50K and TN ∼8K for Pb2Fe2Ge2O9 and Pb2Mn2Ge2O9, respectively, and weak FM nature below Neel temperature. The field dependent properties of both the compounds have been analyzed by drawing the M versus H plots at low and room temperatures. The values of calculated effective magnetic moment 6.07μB and 3.95μB for Fe3+ and Mn3+ ions are in the high spin states (t2g3eg2,s=5/2 and )t2g3eg1,s=2.

Remarks on propagating waves in non-linear vacuum electrodynamics

Using the quadratic expansion in the photon fields of Euler–Heisenberg (EH) non-linear electrodynamics (NLED) Lagrangian model we study relevant vacuum properties in a scenario involving the propagation of a photon probe in the presence of a background constant and static magnetic field, mathbf{B_e}. We compute the gauge invariant, symmetric and conserved energy–momentum tensor (EMT) and angular momentum tensor (AMT) for arbitrary magnetic field strength using the Hilbert method under the soft-photon approximation. We discuss how the presence of magneto-electric terms in the EH Lagrangian is a source of anisotropy, induce the non-zero trace in the EMT and leads to differences between EMT calculated by the Hilbert or Noether method. From the Hilbert EMT we analyze some quantities of interest such as the energy density, pressures, Poynting vector, and angular momentum vector, comparing and discussing the differences with respect to the improved Noether method. The magnetized vacuum properties are also studied showing that a photon effective magnetic moment can be defined for different polarization modes. The calculations are done in terms of derivatives of the two scalar invariants of electrodynamics, hence, extension to other NLED Lagrangian is straightforward. We discuss further physical implications and experimental strategies to test magnetization, photon pressure, and effective magnetic moment.

Crystalline Rhodium‐Tin Complexes with Radical Trianion and Tetraanion Phthalocyanine Ligands: Observation of Nimine(Pc)−Rh Coordination Bond

AbstractCrystalline {Cryptand(Na+)}[(COD)RhICl⋅SnII(Pc3−)]−⋅2C6H4Cl2 (1) and {Cryptand(Cs+)}[(COD)RhI⋅SnII(Pc4−)]−⋅C6H5CH3 (2) complexes were obtained via the interaction of [SnII(Pc3−)]− and [SnII(Pc4−)]2−, respectively, with organometallic {(COD)RhCl}2 dimer (COD is 1,5‐cyclooctadiene). Dissociation of {(COD)RhCl}2 followed by the Rh−Sn binding is observed at the formation of 1. Elimination of the chlorine atom at the rhodium atom is observed in 2, and rhodium is additionally coordinated to the imine nitrogen atom of Pc4−. The complexes contain mono‐ Pc⋅3− and doubly reduced Pc4− species, respectively, that is supported by the data of XRD analysis as well as optical and magnetic properties of 1 and 2. There is an alternation of C‐Nimine bonds in the macrocycles, which gradually increases with increasing negative charge on the macrocycle. The difference between shorter and longer bonds increases from 0.051 Å in Pc3− to 0.075 Å in Pc4−. The formation of 1 is accompanied by an essential blue shift of the Q‐band of starting SnPc and the appearance of a new intense band at 1031 nm. The even stronger shift of the Q‐band is observed in the spectrum of 2, but the band in the near‐IR range becomes weaker. The value of effective magnetic moment of 1 is 1.76 μB at 300 K corresponding the contribution of the Pc3− radical trianions (S=1/2). Only weak magnetic coupling with the Weise temperature of −3 K is observed in 1 due to weak π–π interaction between the macrocycles in the chains. Paramagnetic Pc3− species additionally monitored by EPR spectroscopy show a strong temperature dependence of g‐factor and linewidth of the EPR signal. Complex 2 is diamagnetic and EPR silent.

Single-crystal structure, cation distribution, and optical/magnetic properties of Ce3+-doped Gd3Al2Ga3O12 crystal

Ce-doped Gd3Al2Ga3O12 (Ce3+:GAGG) scintillator finds practical application in industrial computed tomography and medical imaging, however a precise understanding of its single-crystal structure has been lacking. In this study, we grew a 1-inch-sized single crystal with the nominal composition 0.5%Ce3+:GAGG using the Czochralski method. To determine the crystal structure, we employed single-crystal XRD along with element analyses using ICP and XRF-WDS techniques. Our analysis revealed the precise formula of the crystal as 0.1% Ce3+:Gd3(Ga0.543Al0.457)2(Ga0.721Al0.279)3O12. Notably, Ga3+ cations exhibit a stronger preference at the tetrahedral sites compared to Al3+ cations. The optical absorption and luminescence resulting from Ce3+ 4f–5d transitions are cross-validated in the transmission and photoluminescence spectra. From 1.8 to 300 K, Ce:GAGG exhibits paramagnetic behavior and obeys the Curie-Weiss law. The 8S7/2 ground state of Gd3+ ion contributes to the overall effective magnetic moment on the one hand and plays a significant role in energy transfer from Gd3+ and Ce3+ upon excitation on the other hand. The magneto-optical Faraday rotation measurement of Ce:GAGG was performed to determine Verdet constants at 532 nm and 633 nm. These results may help a better understanding and the practical exploitation of Ce3+:GAGG as a multifunctional material in optic and magnetic fields.

Magnetic and Superconducting Phase Diagram of Electron-Doped Eu<sub>2-x</sub>Ce<sub>x</sub>CuO<sub>4+α-δ</sub>

We have investigated the magnetism and superconductivity of the electron-doped Eu2-xCexCuO4+α-δ in a wide range area of doping Ce4+ at 0.09 ≤ x ≤ 0.20 by means of magnetic susceptibility measurement at low temperatures down to 2 K. Superconductivity was observed in the concentration of Ce4+ at 0.12 ≤ x ≤ 0.20 with the range of the reduction of oxygen content 0.0255 ≤ δ ≤ 0.093 with a maximum transition temperature of 12 K. Furthermore, from the data temperature dependence of the dc magnetic-susceptibility, it can be analyzed the Curie constant, atomic magnetic moment and effective magnetic moment in each sample. Those three values have similar values with increasing Ce4+ concentration for a sample that doesn’t show superconductivity.

Anomalous Ferromagnetic Phase in the Gd1−xErxB4 Series: Crystal Growth, Thermal, and Magnetic Properties

Rare-earth tetraborides RB4 are of great interest due to the occurrence of geometric magnetic frustration and corresponding unusual magnetic properties. While the Gd3+ spins in GdB4 align along the ab plane, Er3+ spins in the isomorphic ErB4 are confined to the c–axis. The magnetization in the latter exhibits a plateau at the midpoint of the saturation magnetization. Therefore, solid solutions of (Gd, Er)B4 provide an excellent playground for exploring the intricate magnetic behavior in these compounds. Single crystals of Gd1−xErxB4 (x = 0, 0.2, and 0.4) were grown in aluminum flux. X-ray diffraction scans revealed single-phase materials, and a drop in the unit cell volume with increasing Er content, suggesting the partial substitution of Er at the Gd sites. Heat capacity measurements indicated a systematic decrease of the Néel temperature (TN) with increasing Er content. The effective magnetic moment determined from the magnetization measurement agreed with the calculated free ion values for Gd3+ and Er3+, providing further evidence for the successful substitution of Er for Gd. The partial substitution resulted in an anomalous ferromagnetic phase below TN, exhibiting significant anisotropy, predominantly along the c-axis. This intriguing behavior merits further studies of the magnetism in the Gd1−xErxB4 borides.

Magneto-structural characterization of different kinds of magnetic nanoparticles

Using well-established measurement techniques like transmission electron microscopy (TEM), dynamic light scattering (DLS), small and wide angle X-ray scattering (SAXS, WAXS), susceptometry, and magnetorelaxometry, the distribution of the physical and magnetic size (magnetic moments) and magnetic anisotropy of a variety of structurally different magnetic nanoparticle samples (MNPs) is analyzed and compared. A term which accounts for the presence of weak magnetic areas (WMAs) within the MNPs was introduced to the widespread analysis model for M(H) data, enabling a consistent interpretation of the data in most of the systems. A comparison of the size distributions as obtained for the physical and the magnetic diameter suggests a multidomain structure for three single core systems under investigation, in all probability evoked by the presence of a wustite phase, as identified by WAXS.Analyzing the relationship d < dm < dc between the average single core diameter d, the effective magnetic (domain) size dm and the cluster diameter dc quantitatively, two qualitatively different magnetic structures in multicore MNP (MCMNP) systems were identified: (i) The magnetic moments of single cores within the MCMNP of fluidMAG tend to build flux closure structures, driven by dipole–dipole interaction. (ii) The magnetic behavior of Resovist® was attributed to the presence of domain sizes of about 12 nm within MCMNP, exceeding the single core diameters of 5 nm. Thereby, WAXS revealed a bimodal crystallite size distribution suggesting a crystallite merging process within the MCMNP. The value of the effective magnetic moment of these MCMNP could be explained within the presented “random moment cluster model” (RMCM).We conclude that the combination of physical and magnetic structure parameters obtained from complementary measurement methods allows a reliable assessment of the magnetic structure of single and multicore MNPs.

FexSey@C superlattice nanocrystals for peroxymonosulfate activation: Intrinsic nature of Fe spin state

Two-dimensional layered carbon-coated FexSey nanocrystal superlattices with different crystalline structure (2D FexSey@C NS) are prepared and tested in Fenton-like reaction via PMS activation. The intrinsic nature and properties that govern the activity of 2D FexSey@C NS are deeply elucidated. Experimental analysis and theoretical calculations indicated that the spin state of Fe strongly decided the catalytic activity of 2D FexSey@C NS, and that a high spin state of Fe (4.16 μB) with a large effective magnetic moment not only regulated PMS adsorption (−3.06 eV) for increasing electronic density (0.79 e), but also accelerated interfacial charge transfer for HSO5− decomposition to produce SO4•−. Therefore, among 2D FexSey@C NS, 2D FeSe2 @C NS exhibited the most active performance in PMS activation with brilliant durability and adaptability. The study illustrates a new application of superlattice nanomaterials in environmental remediation and supplies fundamental insight to the intrinsic chemical structure of Fe-based catalysts for PMS activation.

Magnetic properties of SmMn1-xCoxO3 and Sm1-yRyMn0.6Co0.4O3

Polycrystalline SmMn1-xCoxO3 and Sm1-yRyMn0.6Co0.4O3, which have a single orthorhombic perovskite-type structure without any impurities, were prepared by complex polymerization to investigate the effects of A- and B-site element substitutions on the crystal structure and magnetic properties. The unit-cell volume of SmMn1-xCoxO3 decreased with increasing x and that of Sm1-yRyMn0.6Co0.4O3 increased with increasing average radius of A-site ions ⟨rR⟩, and the chemical pressure due to element substitution was observed in these two systems. At 0.0 ≤ x ≤ 0.4 in SmMn1-xCoxO3, a marked increase in the field-cooled magnetization MFC and an increase in the canted-antiferromagnetic transition temperature Tc were observed with increasing x, but they decreased for 0.5 ≤ x ≤ 1.0. However, no specific spin reversal phenomenon was observed, unlike in other RMnO3 compounds. The magnetic susceptibility of both compounds obeyed the Curie–Weiss law with constant susceptibility above 200 K, which was not common in other Sm compounds, and the effective magnetic moment Peff could be easily evaluated. By analyzing Peff of SmMn1-xCoxO3, we determined the electronic states of the ions constituting the sample as Mn3+(high spin, HS), Mn4+, and Co2+(HS) at 0 < x ≤ 0.5 and Mn4+, Co3+(low spin), and Co2+(HS) at 0.5 < x ≤ 0.9. The MFC of Sm1-yRyMn0.6Co0.4O3 decreased with increasing Y and Lu concentrations and increased with La concentration. The Tc and Weiss temperature of Sm1-yRyMn0.6Co0.4O3, both of which increased linearly with increasing ⟨rR⟩, could be attributed to the effects of chemical pressure. Although M − H measurements showed that Sm3+ in Sm1-yRyMn0.6Co0.4O3 was paramagnetic, the Peff analysis results suggested that the excited state of Sm3+ was affected.

Spin-liquid state with precursor ferromagnetic clusters interacting antiferromagnetically in frustrated glassy tetragonal spinel Zn0.8Cu0.2FeMnO4

Spinels (AB 2O4) with magnetic ions occupying only the octahedral B sites have inherent magnetic frustration which inhibits magnetic long-range order (LRO) but may lead to exotic states. Here we report on the magnetic properties of the tetragonal spinel Zn0.8Cu0.2FeMnO4, the tetragonality resulting from the Jahn–Teller active Mn3+ ions. X-ray diffraction and x-ray photoelectron spectroscopy of the sample yielded the composition () A [] B O4‒δ . Analysis of the temperature dependence of magnetization (M), ac magnetic susceptibilities (χ′ and χ′′), dc susceptibility (χ), heat capacity Cp , and neutron diffraction (ND) measurements show complex temperature-dependent short-range order (SRO) but without LRO. The data of χ vs. T fits the Curie–Weiss law: χ = C/(T ‒ θ) from T = 250 K to 400 K with θ ≃ 185 K signifying dominant ferromagnetic (FM) coupling with the FM exchange constant J/k B = 17 K, and C = 3.29 emu K mol‒1 Oe‒1 yielding an effective magnetic moment µ eff = 5.13 µ B resulting from the high-spin states of Cu2+ (A site) and Fe2+ (B site), while the B site trivalent ions Mn3+ and Fe3+ are in their low-spin states. The extrapolated saturation magnetization obtained from the M vs. H data at T = 2 K is explained using the spin arrangement (Cu2+↓) A [Fe2+↑, Fe3+↓, Mn3+↑] B leading to FM clusters interact antiferromagnetically at low temperatures. Temperature dependence of d(χT)/dT shows the onset of ferrimagnetism below ∼100 K and peaks near 47 K and 24 K. The relaxation time τ obtained from temperature and frequency dependence of χ″ when fit to the power law and Vogel–Fulcher laws confirm the cluster spin-glass (SG) state. The magnetic field dependence of the SG temperature follows the equation: with T SG (0) = 46.6 K, A = 8.6 × 10‒3 Oe‒0.593 and = 3.37. The temperature dependence of hysteresis loops yields coercivity HC ∼ 3.8 kOe at 2 K without exchange-bias, but HC decreases with increase in T becoming zero above 24 K, the T SG(H) for H = 800 Oe. Variations of Cp vs. T from 2 K to 200 K in H = 0 and H = 90 kOe do not show any peak characteristic of LRO. However, after correcting for the lattice contribution, a broad weak peak typically of SRO becomes evident centered around 40 K. For T < 9 K, Cp varies as T2 ; a typical signature of spin-liquids (SLs). Comparison of the ND measurements at 1.7 K and 79.4 K shows absence of LRO. Time dependence of thermo-remanent magnetization M TRM(t) studies below 9 K reveal weakening of the inter-cluster interaction with increase in temperature. A summary of these results is that in Zn0.8Cu0.2FeMnO4, ferromagnetic clusters interact antiferromagnetically without LRO but producing a cluster SG state at T SG(0) = 46.6 K, followed by SL behavior below 9 K.