Magnetic Properties Of Polycrystalline Samples Research Articles

Synthesis, Structure and Magnetic Properties of Some Copper(II) Complexes Supported by Pendant Calix[4]arene Ligands

AbstractThe synthesis and characterization of three new calix[4]arene ligands bearing two pendant acylhydrazone arms and some of their Cu2+ complexes, namely [Cu(L1‐2H)(MeOH)] (3), [Cu(L1’‐H)(Cl)(2‐hydroxy‐1‐naphthaldehyde)] (4), [Cu2(L2‐2H)2] (5) and [Cu4(L3‐2H)2(OH)2(ClO4)2] (6) are described. The ligands are obtained by simple imine condensation reactions between calix[4]arene‐1,3‐bis‐acyl‐hydrazides and the corresponding carbaldehydes. The Cu2+ ions are always situated in 5‐membered chelate rings, either in a deprotonated −O−CR=N−N=CHR (enolate) or a neutral O=CR−NH−N=CHR (keto) form. In 3 and 4 a 5‐membered chelate ring is formed through interaction of the Cu2+ ion with the naphtholato group. Additional MeOH, chlorido or naphthaldehyde ligands complete the planar (3) or square pyramidal (4) coordination spheres. The thiophenes in 5 do not interact with the Cu2+ ions and dimerization of [CuL] entities occurs to produce centrosymmetric 2 : 2 complexes with four‐coordinated Cu2+ ions. In 6, two dinuclear [Cu2(L3‐2H)(OH)] subunits are connected by μ1,3‐bridging ClO4− ions. The magnetic properties of polycrystalline samples of 5 and 6 were studied by variable temperature magnetic susceptibility measurements. The χ′′(T) vs T plots indicate antiferromagnetic exchange interactions. The exchange interactions in 6 (J=−4.8 cm−1) were found to be stronger than in 5 (J=−0.54 cm−1). This is also supported by broken symmetry DFT calculations.

Impact of Mn-Pn intermixing on magnetic properties of an intrinsic magnetic topological insulator: the µSR perspective

We investigated the magnetic properties of polycrystalline samples of the intrinsic magnetic topological insulators MnPn2Te4, with pnictogen Pn = Sb, Bi, by bulk magnetization and µSR. DC susceptibility detects the onset of magnetic ordering at TN = 27 K and 24 K and a field dependence of the macroscopic magnetization compatible with ferri- (or ferro-) and atiferro- magnetic ordering, respectively. Weak transverse field (wTF) Muon Spin Rotation (µSR) confirms the homogeneous bulk nature of magnetic ordering at the same two distinct transition temperatures. Zero Field (ZF) µSR shows that the Sb based material displays a broader distribution of internal field at the muon, in accordance with a larger deviation from the stoichiomectric composition and a higher degree of positional disorder (Mn at the Pn(6c) site), which however does not affect significantly the sharpness of the thermodynamic transition, as detected by the muon magnetic volume fraction and the observability of a critical divergence in the longitudinal and transverse muon relaxation rates.

A comparative study on the structural, magnetic and dielectric properties of magnesium substituted cobalt ferrites

The structural, morphological, vibrational, dielectric and magnetic properties of polycrystalline samples of Co 1- x Mg x Fe 2 O 4 ( x = 0.00, 0.02, 0.07, 0.12 and 0.30) acquired from sol-gel process has been reported. Structural studies from Rietveld refinement of XRD patterns verified the development of single-phase samples. Raman spectroscopy shows the presence of additional peaks at 620 cm −1 and 660 cm −1 confirming the mixed–spinel structure. With the increase in Mg 2+ substitution, the saturation magnetization decreases from 77.6 emu/g to 56.9 emu/g while the coercive field initially increases ( x < 0.07) and then decreases from 846 Oe to 742 Oe. Except for the x = 0.30 sample, the impedance spectroscopy shows two relaxation peaks in the rest of the samples. The contribution of electroactive regions such as grains, grain boundaries and electrode effect are identified by the comparative study of impedance and modulus spectroscopy. The Nyquist plots are modeled to equivalent circuits accordingly. The activation energy estimated from modulus spectroscopy and Nyquist plots is found to be comparable. The dielectric constants at 323 K are initially found to increase and then decrease. The ac conductivity is interpreted by considering Jonschers’ Power Law as well as Double Power Law and concluded that the small polaron hopping is responsible for electrical conductivity.

Influence of the orthorhombic phase content on the dielectric and magnetic properties of YMnO3

Here, we report on the dielectric and magnetic properties of polycrystalline samples of YMnO3 where the ratio between both orthorhombic (o-YMO) and hexagonal (h-YMO) phases has been controlled by means of appropriate sintering treatments. Interestingly, we observe that the dielectric behavior is dominated by the presence of the metastable o-YMO phase, even though its amount remains as a minority phase. However it also influences the magnetic behavior for sintering temperatures below 1000 °C, and in addition, a weak ferromagnetic contribution is always detected in our polycrystalline samples regardless of the o-YMO content.

Change in the magnetic properties of polycrystalline thin-film magnetite upon introduction of an iron sublayer

The field dependences of the magnetic moment of polycrystalline magnetite films formed by pulsed laser deposition on a silicon substrate with the addition of an iron sublayer have been investigated. The influence of the sequence of layers Fe/Fe3O4 and Fe3O4/Fe on the magnetic characteristics of these structures has been analyzed. It has turned out that an increase in the saturation magnetization and the formation of a rectangular hysteresis loop with the coercive force acceptable for applications of thin-film magnetite as a hard magnetic electrode of the magnetic tunnel junction are observed only for the sequence of layers Fe/Fe3O4. The effect of the vacuum annealing temperature on the magnetic properties of polycrystalline samples of the Fe/Fe3O4 structure has been studied. It has been found that the best result is achieved at an annealing temperature of 500°C. The phenomenological model describing the magnetic properties of the polycrystalline two-layer magnetic structure Fe/Fe3O4 has been formulated. The results of numerical calculations have demonstrated that the introduction of only two phenomenological anisotropic interactions into the expression for the energy of the film provides a qualitative description of the observed experimental data in the form of hysteresis loops.

Dominant ferromagnetism in the spin-1/2 half-twist ladder 334 compounds, Ba3Cu3In4O12 and Ba3Cu3Sc4O12

The magnetic properties of polycrystalline samples of Ba3Cu3In4O12 (In-334) and Ba3Cu3Sc4O12 (Sc-334) are reported. Both 334 phases have a structure derived from perovskite, with CuO4 squares interconnected to form half-twist ladders along the c-axis. The Cu–O–Cu angles, ∼90°, and the positive Weiss temperatures indicate the presence of significant ferromagnetic (FM) interactions along the Cu ladders. At low temperatures, T < 20 K, sharp transitions in the magnetic susceptibility and heat capacity measurements indicate three-dimensional (3D) antiferromagnetic (AFM) ordering at TN. TN is suppressed on application of a field and a complex magnetic phase diagram with three distinct magnetic regimes below the upper critical field can be inferred from our measurements. The magnetic interactions are discussed in relation to a modified spin-1/2 FM–AFM model and the 334 half-twist ladder is compared to other two-rung ladder spin-1/2 systems.

A Study of Exchange Interactions in R(FeCo)&lt;sub&gt;11&lt;/sub&gt;TiC&lt;sub&gt;y&lt;/sub&gt; (R=Y or Pr) Compounds

The exchange interactions in PrFe11-xCoxTiCy (x=0÷2, y≤1), are analyzed on the basis of the structural and magnetic properties of polycrystalline samples. The magnetic properties of polycrystalline isomorphous compounds YFe11-xCoxTiCy have been used in order to determine the T (T=Fe+Co) sub-lattice contributions, such as the T sub-lattice mean magnetic moment and the T-T exchange interaction strength. The exchange coupling parameters JTT, JRT and the recurrent molecular field coefficients nTT, nRT have been calculated in the molecular field approximation (MCA). The effects of Co content and carbonation on the R-T (T=Fe+Co) and on the T-T exchange interactions are analyzed.

The effect of V substitution on the properties of CoTiSb

Electrical resistivity, structural and magnetic properties of polycrystalline samples of a half-Heusler alloy, CoTiSb, and the effect of the substitution of V for Ti on these properties in CoTi 1 - x V x Sb have been investigated. The temperature dependence of the electrical resistivity in CoTiSb above 10 K is found to exhibit, on the whole, semiconducting behavior, which agrees with previous results. For samples in which V is substituted for Ti with x ⩽ 0.1 the structure is found to be the half-Heusler type as with x = 0 . As V increases from x = 0 to 0.05, the magnitude of the resistivity increases, but the temperature dependence is similar to that of x = 0 . For the sample with x = 0.1 , however, the magnitude of the resistivity suddenly decreases to the value smaller than that of x = 0 , and the slope of the temperature dependence of the resistivity becomes positive down to 25 K.

Superconductivity in magnetically ordered Ru1-xIr xSr2GdCu2O8 compounds

We have performed a systematic study of the structural, transport, and magnetic properties of polycrystalline samples of the magnetic superconductors Ru1-xIr xSr2GdCu2O8; x = 0, 0.02, 0.05, 0.10, and 0.15. The samples were prepared by solid state reaction and sintered at 1060 ºC for 72 h under O2 flow. X-ray diffraction analysis shows that all samples are nearly single phase and that the lattice parameters are independent of Ir content. Transport properties measurements revealed that the Ru substitution by Ir results in a decrease of Tc,onset from ~50 K (x = 0) to ~30 K (x = 0.10). Further addition of Ir (x > 0.10) causes an evolution from metallic to nonmetallic behavior of r(T). We have also found that magnetic order develops in the undoped Ru-1212 materials near T M ~ 130 K. This temperature decreases linearly with increasing Ir content at the rate of ~ -1.6 K / Ir at.%, suggesting that Ir effectively substitutes Ru in the RuO planes. A subtle drop in r(T) is observed close to T M, probably due to the suppression of the spin-flip scattering. The magnetoresistivity measurements revealed that the temperature Tc,zero, in which r(T) ~ 0, decreases rapidly for low applied magnetic fields (H < 2 T), and that this drop becomes much less pronounced in higher magnetic fields (2 < H < 18 T). The appreciable broadening of r(T) curves at low magnetic fields is reminiscent of the behavior in high-Tc materials showing granular behavior, as for example in Sm1.85Ce0.15CuO4-y.

Magnetic properties and magnetic structures of RAgSi (R=Gd–Er) compounds

The magnetic properties of polycrystalline samples of RAgSi compounds have been investigated by neutron diffraction, magnetization and DC susceptibility measurements over the temperature range from 1.5 to 300 K. All title compounds are antiferromagnetic at low temperatures. Neutron diffraction data collected above the respective Néel points confirm that they crystallize in the hexagonal ZrNiAl-type structure. The magnetic structure of TbAgSi has not been determined due to the complexity of the neutron diffraction patterns recorded at low temperatures. The antiferromagnetic structures of DyAgSi, HoAgSi and ErAgSi are described, each by the propagation vector k=[k x, k x, 0] with k x =0.3311(13), 0.3326(7) and 0.5012(28), respectively. The Néel temperatures are 13.4 K in GdAgSi (from the magnetometric measurements), 21.5 K in TbAgSi, 11 K in DyAgSi, 10 K in HoAgSi and 2.6 K in ErAgSi. Magnetization measurements carried out in the temperature range from 4 to 30 K in the presence of external magnetic fields up to 120 kOe show that the metamagnetic phase transitions are induced in GdAgSi, TbAgSi, DyAgSi and HoAgSi.

Magnetostriction of ferrite of the system CuGa xAl xFe 2−2 xO 4 ( x=0.5) with frustrated structure

For the first time behaviour of magnetic properties of polycrystalline samples of ferrite spinels CuGa x Al x Fe 2−2 x O 4 has been studied. It has been found that in the sample with the substitution x=0.5, a transition from the paramagnetic state to the spin-glass state takes place at the temperature T=(485±5) K, and a transition to the frustrated magnetic phase is observed at the temperature T=(445±5) K. This result is in good agreement with conclusions of theoretical works [1–4]. It has been found that the sample with the substitution x=0.5 in frustrated magnetic phase possesses an anomalous high magnetostriction of paraprocess λ para.

Antiferromagnetic ordering in PrCuSn and NdCuSn

The magnetic properties of polycrystalline samples of PrCuSn and NdCuSn, including their magnetic structures, were determined by magnetic and neutron diffraction measurements. Both compounds show the hexagonal, -type crystal structure and are antiferromagnetic at low temperatures. Below K, the sine modulated magnetic structure with the wave vector k = (0.349,0,0) is observed in PrCuSn, while in NdCuSn below K the collinear antiferromagnetic ordering described by the wave vector k = (1/2,0,0) was detected. In both phases the magnetic moments are parallel to the hexagonal c-axis.

Structural, transport and magnetic properties of PrBa 2−xSr xCu 3O 7-δ

Structural, electrical transport and magnetic properties of polycrystalline samples of PrBa 2−xSr xCu 3O 7-δ were investigated. The results were discussed based on the variation of hybridization between Pr ions and O2p of the CuO 2 planes induced by Sr doping.

Superconductivity and magnetism in (Ho xY 1− x)Ni 2B 2C

Superconducting and magnetic properties of polycrystalline samples of the pseudoquarternary system (Ho x Y 1− x )Ni 2B 2C have been investigated by resistance and susceptibility measurements. A linear depression of the superconducting transition temperature with increasing magnetic ordering temperatures was found by variation of the Ho content providing evidence for magnetic pair breaking. This behaviour is analogous to the known scaling with the de Gennes factor of the rare earth elements in the family of quaternary RNi 2B 2C compounds. Both cases are described by a common scaling behaviour including the superconducting and magnetic transition temperatures. A reetrrant behaviour observed for Ho contents x>0.5 results in maximum in the temperature dependence of the upper critical field H c2( T). These results are compared with H c2( T) data of the RNi 2B 2C family ( R=Tm,Er).

Revisited magnetic properties of NpAl 3: Comparison with other cubic AuCu 3-type actinide compounds

The magnetic properties of polycrystalline samples of NpAl 3, having the cubic AuCu 3-type structure, have been re-examined by neutron diffraction and 237Np Mössbauer measurements. They show that, contrary to earlier data (ferromagnetic order at 62.5 K), NpAl 3 orders at T N ≅ 37 K with a type II AF structure and a saturation Np moment of about 1.3 μ B. The ordered moment as well as the induced quadrupolar interaction are close to the values expected for a Γ 5 crystal field ground state of the Np 3+ ions. Comparisons are made with the magnetic behaviour of the AnX 3 (An = U, Np) compounds.

Magnetic properties of the Tb 4+ ion in Li 2TbF 6: Particular crystal chemical behavior within the Li 2MIVF 6 compounds

Magnetic properties of polycrystalline samples of Li 2TbF 6 were studied in high continuous magnetic fields up to 20 Teslas between 1.4 and 300 K. In this new structural type, all the results agree with the calculated Tb 4+ free ion values ( 8S 7 2 ground state multiplet), and the 4+ oxidation state of the terbium ion was unambiguously inferred. The particular crystal chemical behavior of the Tb 4+ ion is discussed using the phase relationship within the series of Li 2 M IVF 6 compounds.

Magnetic phase diagrams and properties of transition metal substituted MnP

The magnetic properties of polycrystalline samples of Mn 1−xT iP (T  Ni, Mo and W for 0.00 ⩽ t ⩽ = 0.40) are studied by magnetic susceptibility and magnetization measurements. The magnetic, composition-temperature phase diagrams are given. The extension of the magnetic ordered phases [ferromagnetic (F) or helimagnetic (H c )] brings additional experimental support for the number of valence electrons as the major factor determining the “strength” of the co-operative modes in transition metal substituted MnP. Mo and W substitution (contrary to the isoelectronic substituent T  Cr) increases the domain of the H c mode, whereas Ni substitution (contrary to T  Fe and Co) stabilizes the F mode.

Magnetic properties in a high continuous magnetic field of the 'frustrated' compound Fe3F8(H2O)2

The new hydrated mixed-valence fluoride FeIIFe2IIIF8(H2O)2 presents an 'idle-spin behaviour' attributed to a topological frustration: the magnetic ordering of the FeIII sublattice occurs at TN=157 K whereas the FeII spins only order below 36 K. In this work, the magnetic properties of polycrystalline samples in the 1.6-300 K temperature range are presented. From magnetic susceptibility experiments, the Curie constant is found, above 200 K, to be smaller than the free-ions value. Under high continuous magnetic fields up to 200 kOe, characteristics are observed: in the 1.6-24 K temperature range a very abrupt transition attributed to the FeII-spin reorientation is found; it is characterised by a large-field hysteresis. To explain this magnetic behaviour, a magnetic structure is proposed and exchange integrals are evaluated. All this work confirms the importance of the role of the frustration.

Magnetic Properties of RhMnSi and CoTiSi

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Magnetic properties of transition metal substituted MnP

The magnetic properties of polycrystalline samples of Mn 1− t T t P ( T = V, Cr, Fe and Co for 0.00 ≦ t ≦ 0.50) are studied by magnetic susceptibility, magnetization and neutron diffraction measurements. The magnetic phase diagrams of the Mn 1− t T t P phases exhibit paramagnetic, ferromagnetic, helimagnetic and spin glass regions depending on temperature and substitution ( T, t). The concentrated spin glass regions observed in Mn 1− t V t P and Mn 1− t Co t P (0.30 ≦ t ≦ 0.50) are believed to result from the disorder in the metal sublattice. The variation of the magnetic moment of the ordered Mn 1− t T t P phases with the substitution ( T, t) is discussed.