Weiss Behavior Research Articles

Critical behavior approaches to 3D-Mean field model of GdPdIn

We report the critical behavior of GdPdIn in the vicinity of the magnetic phase transition through dc-magnetization characterization. The magnetic susceptibility indicates a ferromagnetic (FM) like behavior below the Curie temperature TC= 96 K. Curie–Weiss behavior indicates that the 4f-shells of Gd3+ ions are fully contributing toward the magnetic properties. A second–order ferromagnetic phase transition in GdPdIn has been confirmed from the positive slope of Arrott plots. The critical exponents β= 0.538(2) and γ= 1.077(3) were derived from modified Arrott plots method, while Kouvel–Fisher method yielded β= 0.540(2) and γ= 1.090(2). The third critical exponent value of δ= 2.998(3) is estimated from the critical isotherm at 96 K. The calculated critical exponents value are very close to the mean–field model. The observed critical exponents follow the Widom relation’s δ=1+γ/β. The reliability of obtained critical exponents are examined through the scaling hypothesis. This study also illustrates that exchange interaction (J(r)) in the GdPdIn is found to decay as r−4.5.

Structural and magnetic properties of superconductive YFeSb1.2 compound

The structural and magnetic analysis of the YFeSb[Formula: see text] compound synthesized by the solid-state reaction method was observed. At room temperature, the compound exhibits the ThCr2Si2-type structure with the space group of [Formula: see text]. Low-field DC magnetic susceptibility property of the YFeSb[Formula: see text] compound has been examined. An obvious oscillation of the remanent magnetization, [Formula: see text] with temperature was observed. The YFeSb[Formula: see text] compound exhibits large irreversibility at low fields below the coercivity fields due to freezing spins at low temperatures. At higher temperatures, the susceptibility obeys perfectly to modified Curie–Weiss behavior. Each magnetic ion on a microscopic scale and each magnetic cluster on a nanoscale experience reveal a local random anisotropy.

(Ca0.95Cd0.10)Pd2Cd3, SrPd2Cd3 and (Eu0.95Cd0.10)Pd2Cd3 with YNi2Al3 type structure – crystal chemistry and magnetic hyperfine interactions

Abstract The intermetallic compounds (Ca0.95Cd0.10)Pd2Cd3, SrPd2Cd3 and (Eu0.95Cd0.10)Pd2Cd3 were synthesized from the elements in sealed niobium ampoules in an induction furnace. The polycrystalline samples were characterized through their Guinier powder patterns. The structures were refined from single crystal X-ray diffractometer data: YNi2Al3 type, P6/mmm, a = 984.61(5), c = 455.33(3) pm, wR2 = 0.0216, 376 F 2 values, 21 variables for (Ca0.95Cd0.10)Pd2Cd3, a = 998.55(8), c = 453.65(3) pm, wR2 = 0.0296, 341 F 2 values, 17 variables for SrPd2Cd3 and a = 992.57(4), c = 457.34(2) pm, wR2 = 0.0300, 384 F 2 values, 21 variables for (Eu0.95Cd0.10)Pd2Cd3. The striking crystal chemical motif in the three structures is a planar [PdCd2] Kagome-type layer. The two crystallographically independent Ca (Sr, Eu) atoms have a coordination number of 18 by 6 Pd and 12 Cd atoms. The calcium and europium compound show a small degree of Ca (Eu) substitution by Cd2 dumb-bells with 281 pm Cd–Cd in (Eu0.95Cd0.10)Pd2Cd3. Temperature dependent magnetic susceptibility measurements show Curie–Weiss behaviour (7.63(1) µB/Eu atom) for the europium compound and the onset of ferromagnetic ordering at T C = 14.9(2) K. The divalent character of europium is corroborated by 151Eu Mössbauer spectroscpy.

Hydrothermal Synthesis and Magnetic Properties of Zn/Mn Oxides Nano Particles

The aim of this study was to investigate the magnetic properties of mixed nanocrystalline Zn/manganese oxide compounds synthesized by a hydrothermal method. These compounds are designed as (ZnO)1−n(MnO)n, where index n ranges from 0.05 to 0.60. The results of magnetic measurements, including AC magnetic susceptibility as a function of temperature (up to 160 K) and frequency (from 7 Hz up to 9970 Hz), as well as DC magnetization in magnetic fields up to 9 T and temperature up to 50 K, are reported. We observed various types of magnetic behavior depending on the nominal weight content of MnO. Samples with a low nominal content (up to n = 0.10) of MnO exhibited Curie–Weiss behavior at higher temperatures. For samples with high nominal weight contribution (from n = 0.30 to 0.60), spin-glass-like or/and weak ferromagnetic behavior is observed.

Ferrimagnetic Clusters as the Origin of Anomalous Curie–Weiss Behavior in ZnFe2O4 Antiferromagnetic Susceptibility

Different studies carried out in the last three decades on the magnetic susceptibility of the spinel ZnFe2O4 ferrite have revealed the positive character of its Curie–Weiss temperature, contradicting its observed antiferromagnetic behavior which is characterized by a well-defined susceptibility peak centered around the Neel temperature (10 K). Some approaches based on ab initio calculations and mixture of interactions have been attempted to explain this anomaly. This work shows how for very low values of the inversion parameter, the small percentage of Fe atoms located in tetrahedral sites gives rise to the appearance of ferrimagnetic clusters around them. Superparamagnetism of these clusters is the main cause of the anomalous Curie–Weiss behavior. This finding is supported experimentally from the thermal dependence of the inverse susceptibility and its evolution with the degree of inversion.

Mechanochemical Synthesis and Magnetic Characterization of Nanosized Cubic Spinel FeCr2S4 Particles.

Nanosized samples of the cubic thiospinel FeCr2S4 were synthesized by ball milling of FeS and Cr2S3 precursors followed by a distinct temperature treatment between 500 and 800 °C. Depending on the applied temperature, volume weighted mean (Lvol) particle sizes of 56 nm (500 °C), 86 nm (600 °C), and 123 nm (800 °C) were obtained. All samples show a transition into the ferrimagnetic state at a Curie temperature TC of ∼ 167 K only slightly depending on the annealing temperature. Above TC, ferromagnetic spin clusters survive and Curie–Weiss behavior is observed only at T ≫ TC, with T depending on the heat treatments and the external magnetic field applied. Zero-field-cooled and field-cooled magnetic susceptibilities diverge significantly below TC in contrast to what is observed for conventionally solid-state-prepared polycrystalline samples. In the low-temperature region, all samples show a transition into the orbital ordered state at about 9 K, which is more pronounced for the samples heated to higher temperatures. This observation is a clear indication that the cation disorder is very low because a pronounced disorder would suppress this magnetic transition. The unusual magnetic properties of the samples at low temperatures and different external magnetic fields can be clearly related to different factors like structural microstrain and magnetocrystalline anisotropy.

Curie–Weiss behavior of the low-temperature paramagnetic susceptibility of semiconductors doped and compensated with hydrogen-like impurities

For the first time, a quantitative model of the Curie–Weiss behavior of a low-temperature paramagnetic susceptibility of electrically neutral donors in n-type diamagnetic covalent semiconductors is proposed. The exchange interaction between nearest two neutral donors was calculated with the use of the Heitler–London model. In this model, we take into account the change in the thermal ionization energy of donors due to the shift of the bottom of the conduction band to the bandgap with doping and compensation. The energy of the exchange spin–spin interaction between electrons localized on donors is calculated as a function of the donor concentration and the degree of their compensation by acceptors. The broadening of the donor band due to the Coulomb interaction of the nearest impurity ions was taken into account. We considered crystals of n-type germanium doped with arsenic up to the concentration close to the insulator–metal phase transition (Mott transition) and compensated with gallium. The compensation ratio K is the ratio of the concentration of compensating acceptors KN to the concentration of doping donors N. The model predicts a change in the sign of the Curie–Weiss temperature from minus to plus (a transition from the antiferromagnetic to ferromagnetic local ordering of electron spins on donors) for K ≈ 0.15–0.3, reaching its maximum positive values of ≈1.3 K for K ≈ 0.5 with the following decrease (a transition to paramagnetism) for K > 0.85. The calculated behavior of the paramagnetic susceptibility of donors is consistent with the experimental data for compensated n-Ge:As,Ga samples close to the Mott transition.

Structure, Magnetic Properties, and 151 Eu Mössbauer Spectra of the Indium‐rich Phase Eu 3 Rh 2 In 15

Structure, Magnetic Properties, and ¹⁵¹ Eu Mössbauer Spectra of the Indium‐rich Phase Eu ₃ Rh ₂ In ₁₅

Quantum Phase Transitions in an Yb-based Semiconductor YbCuS2 with an Effective Spin-1/2 Zigzag Chain

Magnetic properties of an Yb-based semiconductor YbCuS2 with a zigzag chain of Yb3+ ions were studied. The Curie–Weiss behavior of the magnetic susceptibility χ(T) indicates antiferromagnetic interaction and an isolated Kramers doublet ground state with effective spin-1/2. Magnetic specific heat Cm/T exhibits a sharp peak at TO = 0.95 K, where the magnetic entropy is 20% of R ln 2, indicating strong magnetic fluctuations. In magnetic fields, TO is robust for B < 4 T, and it shifts to higher temperatures but reverses downward for B ≥ 7 T. Below TO, a magnetization plateau manifests itself at around 6 T which is followed by transitions at 9.1 and 15.6 T. The phase diagram suggests that nontrivial phases arise from magnetic frustration in the Yb zigzag chain.

Solid solutions EuAu4Cd2−x Mg x with a remarkably stable ferromagnetic ground state

Abstract Samples of the solid solutions EuAu4Cd2−x Mg x were synthesized from the elements in sealed tantalum ampoules. The elements were reacted at a maximum temperature of 1273 K followed by slow cooling. For crystal growth, the polycrystalline samples were ground to powders, pressed to pellets and annealed again. All samples crystallize with the tetragonal YbAl4Mo2-type structure, space group I4/mmm. The solid solution extends up to x = 1 and the Cd/Mg substitution has only a minor influence on the lattice parameters. The samples have been characterized by powder X-ray diffraction and the structure of EuAu4Cd1.58(2)Mg0.42(2) was refined from single crystal X-ray diffractometer data: a = 715.46(14), c = 549.96(11) pm, wR2 = 0.0334, 180 F 2 values and 11 variables. The striking crystal chemical motifs of the EuAu4Cd2−x Mg x structures are Eu@Au12 and (Cd/Mg)@Au8(Cd/Mg)2 polyhedra and linear Cd/Mg chains in form of a tetragonal rod packing with distances of 275 pm for Cd/Mg–Cd/Mg. Temperature dependent magnetic susceptibility measurements of all samples from the solid solutions EuAu4Cd2−x Mg x revealed Curie–Weiss behavior and stable divalent europium. All samples are ordered ferromagnetically around T = 16 K, and magnetization isotherms at 3 K classify these materials as soft ferromagnets. It is remarkable that the structural Cd/Mg disorder within the chains does not influence the ferromagnetic ground state. The divalent nature of europium in these intermetallics was exemplarily studied for the EuAu4Cd1.4Mg0.6 sample by 151Eu Mössbauer spectroscopy. At 6 K the isomer shift is −9.95(4) mm s−1 and one observes full magnetic hyperfine field splitting with B hf = 27.1(1) T.

Collective excitations and field induced anti-ferroelectric modes in chiral liquid crystal dimer

Collective excitations and field influence are investigated in tilted or orthogonal layered liquid crystal smectic (Sm) phases in a chiral hydrogen bonded (HB) calamitic dimer 10OBA:M*SA:10OBA by low-frequency dielectric spectroscopy. Phase transition temperatures, hysteresis, and phase thermal ranges are determined. The hysteresis in SmC* reveals the storage device suitability. The magnitude of the tilt angle in SmC* infers moderate viewing angle. The growth of primary order parameter tilt angle θ(T) infers long range interaction in SmC*. The growth of ferroelectric (FE) relevant secondary order parameter polarization Ps(T) infers strong layer-over-layer helical coupling of transverse dipole moment μt. Dispersion (loss vs permittivity) in 1D SmC*, 3D orthogonal SmBcryst, and 3D hexagonal tilted SmG crystal phases infers two distinct collective modes, viz., high frequency soft mode (SM) and low frequency Goldstone mode (GM). The dielectric strength of the SM in the SmC* phase confirms the FE Curie–Weiss behavior. The GM persists down to low temperature 3D LC phases. The AF order in SmC* is smeared by high temperature thermal fluctuations. A bias field resolves the GM in SmC* to reveal antiferroelectric (AF) modes. AF order manifested as GM1 and GM2 is explained by distinct Ps helices with different relaxation frequencies fR1 and fR2. GM1 and GM2 in 3D SmBcryst and SmG phases are explained by quenching by crystal field. HB LC dimer with a just shifted chiral center promoted the occurrence of field induced AF modes. AF P-switching in SmC* infers the gray scale mode. Trends of dielectric parameters, relaxation frequency, loss maximum, activation energy, dielectric strength, distribution parameter, etc., are discussed with respect to utility in appliances.

A new sodium- and manganese-based trivanadate NaMn2V3O10: synthesis, structural and magnetic insights

Single crystals of the new compound, NaMn2V3O10, were grown by conventional solid-state reaction. The crystal structure of the synthesized sample was determined using single-crystal X-ray diffraction data. NaMn2V3O10 crystallizes in the triclinic system with space group P$$\stackrel{-}{1}$$ and cell parameters a = 6.854 (2) A, b = 6.877 (2) A, c = 9.716 (2) A, α = 100.604 (1)°, β = 104.169 (1)°, and γ = 101.390 (1)°. The structure of this vanadate built up from the connection of V3O10 groups and MnO6 octahedra via corners leading to an open three-dimensional framework delimiting tunnels along [001] direction, where the Na+ cations are localized. The powder of NaMn2V3O10 was prepared by Pechini method. The magnetic measurement has been evidenced by Curie–Weiss behavior above 4.5 K with θ = − 25.46 K demonstrating the occurrence of predominant antiferromagnetic interactions between Mn2+ cations.

Effect of fluorinated achiral chain length on structural, dielectric and electro-optic properties of two terphenyl based antiferroelectric liquid crystals

Two antiferroelectric liquid crystals of different fluorinated chain length have been studied. Although both exhibit antiferroelectric (SmCA*), ferroelectric (SmC*) and paraelectric (SmA*) phases, melting point decreases with increasing achiral chain length but clearing point shows opposite trend. Thermal ranges of SmCA* and SmC* phases exhibit odd-even effect like the dipole moments and spontaneous polarization. Layer spacings, average intermolecular distances and correlation lengths across the smectic planes also increase with chain length. Temperature dependence of layer spacings, x-ray tilt, optical tilt and spontaneous polarization suggest tricritical nature of SmC*–SmA* transition. Dielectric increments decrease with increased achiral chain. Both soft mode and Goldstone mode critical frequencies decrease with decreasing temperature in the lower derivative but opposite behaviour is observed in the higher derivative. Both the compounds show Curie–Weiss behaviour in soft mode near SmC*–SmA* transition temperature (Tc). Goldstone mode critical frequency is much higher in the higher derivative. Both in-phase and anti-phase antiferroelectric modes are observed in SmCA* phase in the higher derivative but in the lower derivative only anti-phase antiferroelectric mode is observed. Optical tilts suggest orthoconic nature of the SmCA* phase of both the compounds. Ferroelectric-antiferroelectric transition temperature decreases with increasing ac field in both compounds.

EuPtSn2 – A Stannide with Sn2 Dumbbells in a Three‐dimensional [PtSn2]2– Polyanion

EuPtSn2 was obtained by melting of the elements in a sealed tantalum ampoule followed by an annealing sequence for crystal growth. The EuPtSn2 sample was studied through its Guinier powder pattern and the structure was refined from single‐crystal X‐ray diffractometer data: CeRhSn2 type, Cmcm, a = 472.05(3), b = 1724.19(12), c = 957.36(7) pm, wR2 = 0.0388, 879 F2 values and 30 variables. The platinum and tin atoms build up a three‐dimensional [PtSn2]2– polyanionic network which consists of distorted PtSn5 square pyramids (265–278 pm Pt–Sn) and Sn2 dumbbells with 281 and 299 pm Sn–Sn distances. The structural relationship with DyRhGe2 and Ce3Pt4Ge6 is discussed. EuPtSn2 shows Curie–Weiss behavior with an experimental magnetic moment of 7.78(1) μB / Eu, indicating stable divalent europium. This is corroborated by 151Eu Mössbauer spectroscopy. Antiferromagnetic ordering is detected below 3.4 K. Specific heat measurements confirm the magnetic ordering and indicate a second phase transition through a clear λ‐type signal at 7.3 K which might be associated with a structural distortion.

Ternary platinides Sr4In13Pt9 and Eu5In9Pt7

Sr4In13Pt9 and Eu5In9Pt7 were synthesized by induction melting of the pure elements in glassy carbon crucibles. Both compounds were characterized through their X-ray powder patterns and the structures were refined from X-ray single crystal diffractometer data: Ho4Ir13Ge9 type, Pmmn, a = 439.17(5) pm, b = 1232.2(2) pm, c = 2135.3(3) pm, wR2 = 0.0550, 3598 F2 values, 88 variables for Sr4In13Pt9 and Sc5Pt9Si7 type, $$P{\bar{6}}$$ , a = 1116.7(2) pm, c = 435.86(7) pm, wR2 = 0.0379, 1358 F2 values, 45 variables for Eu5In9Pt7. The platinum and indium atoms form covalently bonded [In13Pt9] and [In9Pt7] polyanionic networks which exhibit larger tunnels for the strontium and europium cations. They bind to these networks through electrostatic interactions as is evident from shorter Sr–Pt (339–353 pm) and Eu–Pt (298–334 pm) contacts. Temperature-dependent magnetic susceptibility measurements of Eu5In9Pt7 show Curie–Weiss behavior with an experimental magnetic moment of 7.51(1) µB/Eu, indicating stable divalent europium. This is corroborated by 151Eu Mossbauer spectroscopy. Eu5In9Pt7 orders antiferromagnetically at 11.6(5) K and shows a metamagnetic transition in the 2.5 K isotherm at a critical field of 2 kOe.

Magnetic behavior, Griffiths phase and magneto-transport study in 3d based nano-crystalline double perovskite Pr2CoMnO6

Double perovskite (DP) oxide material receive extensive research interest due to exciting physical properties with potential technological application. 3d based DP oxides are promising for exciting physics like magnetodielectric, ferroelectric, Griffiths phase, etc., specially Co/Mn DPs are gaining much research interest. In this paper we present the study of magnetic phase and transport properties in nano-crystalline Pr2CoMnO6 a 3d based double perovskite compound. This material shows a paramagnetic (PM) to ferromagnetic (FM) phase transition below 173 K marked by a rapid increase in magnetic moment due to spin ordering. We found divergence in inverse magnetic susceptibility (χ−1) from Curie–Weiss behavior around 206 K which indicates the evolution of Griffiths phase before actual PM-FM transition. We found that the Griffiths phase suppressed with increasing applied magnetic field. For the understanding of charge transport in this material we have measured temperature dependent electrical resistivity. Pr2CoMnO6 is a strong insulator where resistivity increase abruptly below magnetic phase transition. To understand the effect of magnetic field on transport behavior we have also measured the magnetoresistance (MR) at different temperatures. Sample shows the negative MR with maximum value ∼22% under applied magnetic field of 50 kOe at 125 K. MR follows quadratic field dependency above Tc however below Tc the MR shows deviation from this field dependency at low field.

Microscopic investigation of low dimensional magnet Sc2Cu2O5: combined experimental and ab initio approach

Sc2Cu2O5 is a non centro-symmetric oxide comprising of zig-zag chains made up of Cu2+ ions in a distorted square planer coordination. We present here a combined experimental and theoretical investigation on this compound, which is based on magnetization, electron spin resonance (ESR), heat capacity as well as density functional theory (DFT) based calculations. Short range magnetic correlation prior to the long range order at K is evidenced by a broad hump like feature (43 K) found in the magnetic contribution of the heat capacity as well as by deviations from a regular Curie–Weiss behavior observed in the bulk magnetization and the Cu2+ ESR intensity. The DFT results indicate the existence of ferro-orbital ordering at the Cu-sites, which gives rise to chain like arrangements of Cu ions along the crystallographic b axis. It also signifies complex nature of the spin structure with nonuniform magnetic interactions along the zig-zag chains. The ground state energy is found to be minimum for ferromagnetically coupled spin-dimers along the chains, whereas the adjacent chains are themselves antiferromagnetically coupled. The experimentally observed short range magnetic correlations possibly arise due to this chain like structure.

A novel cage for actinides: A6W4Al43 (A = U and Pu)

We report on synthesis and characterization of the compounds A6W4Al43 (A = U and Pu), that form in the hexagonal Ho6Mo4Al43 caged-structure family. The A ions reside within W/Al cages where the A–A nearest neighbors form dimers between adjacent W/Al cages, with U–U and Pu–Pu distances of 3.3892 and 3.4080 , respectively. While the W/Al networks provide environments similar to those of other cage-like materials (e.g. filled skutterudites), the atomic displacement parameters from single crystal x-ray diffraction measurements show that the A-ions do not exhibit rattling behavior. We find that there is site interchange disorder on one of the W/Al sites. Magnetic susceptibility measurements show that U6W4Al43 displays anisotropic Curie–Weiss behavior where it fits to the data yield an effective magnetic moment near 2.0 /U. At low temperatures the magnetic susceptibility deviates from the Curie–Weiss temperature dependence and eventually saturates to a constant value. In contrast, Pu6W4Al43 displays nearly temperature independent Pauli paramagnetism for all temperatures, as would be expected if the 5f -electrons are delocalized. The electrical resistivity for U6W4Al43 increases slightly with the decreasing temperature, suggesting that it is dominated by f -electronic hybridization effects and disorder scattering that originates from the W/Al site interchange. Specific heat measurements for U6W4Al43 further reveal an enhanced electronic Sommerfeld coefficient that is consistent with a moderately enhanced charge carrier effective mass. Together these measurements expose these materials as hosts for unstable f -electron magnetism, where the novel cage-like structures control the phenomena through the spacing between the A ions. Through this combination of mild magnetism, the low cost elements of the Al–W cages, and chemical tunability that has been shown for related materials in the same structure, the A6W4Al43 compounds emerge as promising nuclear waste-forms for transuranics, while the wider family of materials makes an appealing environment for studying f -electron physics in a novel structure.

Synthesis and Magnetic Study of Nano-Crystalline Gd2CoMnO6

3d based double perovskite (DP) oxides having great research interest due to their physical properties with some great technological application. Magnetodielectric, magnetocaloric effect, ferroelectric, exotic magnetic phases etc are some properties that double perovskite materials shows, thus received attention of researchers. Magnetic refrigeration is the great cooling technology based on magnetocaloric effect due to high energy efficiency and environmental friendly. Recently, it is found that Gadolinium (Gd) have magnetic refrigerant properties because of large magnatochloric effects at room temperature. In this paper we present the double perovskite Gd2CoMnO6 nano-crystalline which was prepared by sol gel method and its magnetic properties studied by vibrating sample magnetometer (VSM). There is a paramagnetic to ferromagnetic phase transition observed in the sample. We found that paramagnetic Curie-Weiss temperature of Gd2CoMnO6 is around Tc = 131.27 K. Further, temperature dependent inverse magnetic susceptibility (χ −1) shows deviation from curie Weiss behavior around TG ∼ 213 K which is depicts that Griffiths phase singularities is present in this material.

On the deviation from a Curie–Weiss behavior of the ZnFe2O4 susceptibility: A combined ab-initio and Monte-Carlo approach

We present a numerical study of the magnetic properties of ZnFe2O4 using Monte-Carlo simulations performed considering a Heisenberg model with antiferromagnetic couplings determined by Density Functional Theory. Our calculations predict that the magnetic susceptibility has a cusp-like peak centered at 13 K, and follows a Curie–Weiss behavior above this temperature with a high and negative Curie–Weiss temperature (ΘCW=−170 K). These results agree with the experimental data once extrinsic contributions that give rise to the deviation from a Curie–Weiss law are discounted. Additionally, we discuss the spin configuration of ZnFe2O4 below its ordering temperature, where the system presents a high degeneracy.