Range Magnetic Order Research Articles

Anomalous specific heat, magnetic, and electrical transport properties around magnetic instability in Ce3−xLaxCo4Sn13

Ce3Co4Sn13 exhibits interesting physical properties including a large increase in the magnetic specific heat, ΔC(T)/T, at low-temperatures with a maximum value of about 4JK−2molCe−1 and a cross-over from heavy fermion behavior with antiferromagnetic correlations at low magnetic field to single impurity Kondo behavior by applying the field larger than ∼3 T. In order to study the expected quantum criticality of Ce3Co4Sn13 we investigated electrical resistivity, magnetoresistivity, magnetic susceptibility and specific heat of Ce3−xLaxCo4Sn13 and showed that partial substitution of Ce by La does not lead to long range magnetic order, and the low-temperature properties are not typical of the quantum critical point (QCP). The magnetoresistivity of Ce3−xLaxCo4Sn13 has a conventional Kondo character. With increasing of the magnetic field resistivity follows power-law behavior over one decade in temperature for the samples with x ≠ 0 of the series, and exponent n in ρ ∼ Tn is strongly field dependent. The low-temperature specific heat of Ce3−xLaxCo4Sn13 exhibits evolution from a magnetically correlated heavy fermion state to a single impurity state at the critical concentration x = xC = 0.6, however, for xC the C(T)/T behavior is not typical for QCP. The low-temperature resistivity and magnetic susceptibility data give evidence for changeover from Kondo lattice to a single-ion Kondo behaviour at xC, when the La content in Ce3−xLaxCo4Sn13 increases.

Investigations of the singlet ground state system: PrIrSi3

We report our comprehensive study of physical properties of a ternary intermetallic compound PrIrSi3 investigated by dc magnetic susceptibility χ(T), isothermal magnetization M(H), thermo-remnant magnetization M(t), ac magnetic susceptibility χac(T), specific heat Cp(T), electrical resistivity ρ(T), muon spin relaxation (µSR) and inelastic neutron scattering (INS) measurements. A magnetic phase transition is marked by a sharp anomaly at Ttr = 12.2 K in χ(T) measured at low applied fields which is also reflected in the Cp(T) data through a weak anomaly at 12 K. An irreversibility between the zero field cooled and field cooled χ(T) data below 12.2 K and a very large relaxation time of M(t) indicates the presence of ferromagnetic correlation. The magnetic part of specific heat shows a broad Schottky-type anomaly near 40 K due to the crystal electric field (CEF) effect. An extremely small value of magnetic entropy below 12 K suggests a CEF-split singlet ground state which is confirmed from our analysis of INS data. The INS spectra show two prominent inelastic excitations at 8.5 meV and 18.5 meV that could be well accounted by a CEF model. The CEF splitting energy between the ground state singlet and the first excited doublet is found to be 92 K. Our µSR data reveal a possible magnetic ordering below 30 K, which is much higher than that found from the specific heat and magnetic susceptibility measurements. This could be due to the presence of short range correlations well above the long range magnetic ordering or due to the electronic changes induced by muons. The induced moment magnetism in the singlet ground state system PrIrSi3 with such a large splitting energy of 92 K is quite surprising.

Interplay of disorder and antiferromagnetism in TlFe1.6+δ(Se1−xSx)2 probed by neutron scattering

The effect of selenium substitution by sulphur on the structural and physical properties of antiferromagnetic TlFe1.6+δSe2 has been investigated via neutron, x-ray and electron diffraction, and transport measurements. The super-cell related to the iron vacancy ordering found in the pure TlFe1.6Se2 selenide is also present in the S-doped TlFe1.6+δ(Se1−xSx)2 compounds. Neutron scattering experiments show the occurrence of the same long range magnetic ordering in the whole series i.e. the ‘block checkerboard’ antiferromagnetic structure. In particular, this is the first detailed study where the crystal structure and the antiferromagnetic structure is characterized by neutron powder diffraction for the pure TlFe1.6+δS2 sulphide over a large temperature range. We demonstrate the strong correlation between occupancies of the crystallographic iron sites, the level of iron vacancy ordering and the occurrence of block antiferromagnetism in the sulphur series. Introducing S into the Se sites also increases the Fe content in TlFe1.6+δ(Se1−xSx)2 which in turn leads to the disappearance of the Fe vacancy ordering at x = 0.5 ± 0.15. However, by reducing the nominal Fe content, the same vacancy ordering and antiferromagnetic order can be recovered also in the pure TlFe1.6+δS2 sulphide with a simultaneous reduction in the Néel temperature from 435 K in the selenide TlFe1.75Se2 to 330 K in the sulphide TlFe1.5S2. The magnetic moment remains high at low temperature throughout the full substitution range, which contributes to the absence of superconductivity in these compounds.

Dielectric relaxations in La2NiMnO6 with signatures of Griffiths phase

Polycrystalline La2NiMnO6 prepared by sol–gel auto combustion technique is found to possess dual crystallographic phases R-3c (71 vol. %) and Pbnm (29 vol. %), with respective ferromagnetic transitions at 277 K and 160 K, respectively. The impedance data are analysed via Havriliak-Negami equivalent for impedance (HNEI). Using HNEI equation, the resistance “R,” relaxation time “τ,” and symmetric “α” and asymmetric “β” broadening parameters, for the two crystallographic phases are obtained. The dielectric relaxations for the two crystallographic phases are found to be independent of each other. The activation energy of relaxation for the R-3c and Pbnm phases is found to be 147 meV and 88 meV, respectively. Strong correlations of dielectric relaxations with the magnetic phases are seen. Before the onset of ferromagnetic transition, i.e., above 160 K for Pbnm and 277 K for R-3c phase, relaxations are dominantly non-Debye type. Once the ferromagnetic state is achieved, relaxations attain Debye nature. Hopping type conduction mechanism is confirmed from electrical transport measurements: nearest neighbour hopping near room temperature and gradual transition to variable range hopping (VRH) at low temperature. Signature of short range magnetic ordering, reminiscent to Griffiths like phase, is seen in the temperature range 295 K > T > 277 K.

Coexistence of long range magnetic order and intervalent state of Eu in EuCu2(Si x Ge1 − x )2: Evidence from neutron diffraction and spectroscopic studies

Experimental results of the Xray absorption spectr oscopy, Mossbauer spectroscopy (isomer shift) and neu� tron diffraction are presented for the series of EuCu2(SixGe 1- x)2 polycrystalline samples (0 < x < 0.75). Homogeneous intermediate valence state is established for Eu ions as well as long range magnetically ordered state at the temperatures below 10-15 K. Observation of the ordered magnetic moments at Eu site gives rise to the experimental statement for the coexistence of valence fluctuations and long range magnetic order takes place in the wide range of Ge concentrations for this substance.

Spin-lattice dynamics simulation of external field effect on magnetic order of ferromagnetic iron

Modeling of field-induced magnetization in ferromagnetic materials has been an active topic in the last dozen years, yet a dynamic treatment of distance-dependent exchange integral has been lacking. In view of that, we employ spin-lattice dynamics (SLD) simulations to study the external field effect on magnetic order of ferromagnetic iron. Our results show that an external field can increase the inflection point of the temperature. Also the model provides a better description of the effect of spin correlation in response to an external field than the mean-field theory. An external field has a more prominent effect on the long range magnetic order than on the short range counterpart. Furthermore, an external field allows the magnon dispersion curves and the uniform precession modes to exhibit magnetic order variation from their temperature dependence.

Comprehensive study of the spin-charge interplay in antiferromagnetic La2−xSrxCuO4

The origin of the pseudogap and its relationship with superconductivity in the cuprates remains vague. In particular, the interplay between the pseudogap and magnetism is mysterious. Here we investigate the newly discovered nodal gap in hole-doped cuprates using a combination of three experimental techniques applied to one, custom made, single crystal. The crystal is an antiferromagnetic La(2-x)Sr(x)CuO4. with x=1.92%. We perform angle-resolved photoemission spectroscopy measurements as a function of temperature and find: quasi-particle peaks, Fermi surface, anti-nodal gap and below 45 K a nodal gap. Muon spin rotation measurements ensure that the sample is indeed antiferromagnetic and that the doping is close, but below, the spin-glass phase boundary. We also perform elastic neutron scattering measurements and determine the thermal evolution of the commensurate and incommensurate magnetic order, where we find that a nodal gap opens well below the commensurate ordering at 140 K, and close to the incommensurate spin density wave ordering temperature of 30 K.

Floating-zone growth and characterization of triangular lattice antiferromagnetic α-SrCr2O4 crystals

The triangular S=3/2 antiferromagnetic α-phase MCr2O4 (M=Ca, Sr, Ba) family has received increasing attention for their low dimensional geometrically frustrated magnetism. For the first time, the single crystals of α-SrCr2O4 were successfully grown by the floating-zone method. The plate-like crystals are highly a-axis oriented with a 60° twinning structure in the bc plane. We also investigated the magnetic susceptibilities, specific heat and dielectric properties systematically. Our results confirm a long range magnetic ordering emerging in α-SrCr2O4 below about 43K. These crystals are suitable for the future neutron scattering experiments and other in-depth physical measurements.

Soft ferromagnetism in mixed valence Sr1−xLaxTi0.5Mn0.5O3perovskites

The structural, magnetic and electrical properties of the mixed Ti-Mn oxides Sr(1-x)La(x)Ti(0.5)Mn(0.5)O3 (0 ≤ x ≤ 0.5) are reported. At room temperature the oxides have a cubic structure in space group Pm3m for x ≤ 0.25 and rhombohedral in R3c for 0.3 ≤ x ≤ 0.50. X-ray absorption spectroscopic measurements demonstrate the addition of La(3+) is compensated by the partial reduction of Mn(4+) to Mn(3+). Variable temperature neutron diffraction measurements show that cooling Sr(0.6)La(0.4)Ti(0.5)Mn(0.5)O3 results in a first order transition from rhombohedra to an orthorhombic structure in Imma. Complex magnetic behaviour is observed. The magnetic behaviour of the mixed valent (Mn(3+/4+)) examples is dominated by ferromagnetic interactions, although cation disorder frustrates long range magnetic ordering.

Dielectric and magnetic investigations on novel P-2 type layered oxides

This paper is about the investigation and analysis of dielectric and magnetic properties of the curious and promising P-2 layered oxides mainly for electrodes in rechargeable batteries.A solid state synthesis of the novel materials is taken up by taking NFMO as the guiding standard.Two more variants NMCO and NFCO are also synthesized.The structure is confirmed by xrd.The dielectric properties are studied by the cryostat apparatus and a high dielectric constant is observed.In the magnetic studies done by SQUID there is no long range magnetic ordering observed ,but an antiferromagnetic like transition is seen.

A detailed study of the magnetic phase transition in CuCrO2

The phase transition in CuCrO2 to an ordered magnetic state is studied with bulk measurements and elastic and inelastic neutron scattering techniques. The reported onset of spontaneous electric polarization at T = 23.5 K coincides with the appearance, on cooling, of elastic magnetic scattering. At higher temperatures long range magnetic correlations gradually develop but they are dynamic. The ground state is characterized by three-dimensional long range magnetic ordering but along the c direction the correlation length remains limited to ∼200 Å.

Enhanced ferromagnetism in CuO nanowires on the top of CuO nanograins

CuO nanograins (NGs) and CuO nanowires (NWs) on the top of nanograins samples were produced by the electrical resistive heating method. The NGs sample shows absence of long range magnetic order and strong field-induced ferromagnetic behavior. In the sample comprised of NWs on the top of NGs, a long-ranged antiferromagnetic ordering is induced by a magnetic field of 5 kOe and coexists with an enhanced ferromagnetic-like contribution. The ferromagnetic behavior is observed below and above the temperature-induced TN suggesting that this behavior is not dependent on the original magnetic state of the system, whether it is paramagnetic (PM) or antiferromagnetic.

Neutron scattering and muon spin relaxation measurements of the noncentrosymmetric antiferromagnetCeCoGe3

The magnetic states of the non-centrosymmetric, pressure induced superconductor CeCoGe3 have been studied with magnetic susceptibility, muon spin relaxation(muSR), single crystal neutron diffraction and inelastic neutron scattering (INS). CeCoGe3 exhibits three magnetic phase transitions at T_N1 = 21 K, T_N2 = 12 K and T_N3 = 8 K. The presence of long range magnetic order below T_N1 is revealed by the observation of oscillations of the asymmetry in the muSR spectra between 13 K and 20 K and a sharp increase in the muon depolarization rate. Single crystal neutron diffraction measurements reveal magnetic Bragg peaks consistent with propagation vectors of k = 2/3 between T_N1 and T_N2, k = 5/8between T_N2 and T_N3 and k = 1/2 below T_N3. An increase in intensity of the (1 1 0) reflection between T_N1 and T_N3 also indicates a ferromagnetic component in these phases. These measurements are consistent with an equal moment, two-up, two-down magnetic structure below T_N3, with a magnetic moment of 0.405(5) mu_B/Ce. Above T_N2, the results are consistent with an equal moment, two-up, one-down structure with a moment of 0.360(6) mu_B/Ce. INS studies reveal two crystal-field (CEF) excitations at 19 and 27 meV. From an analysis with a CEF model, the wave-functions of the J = 5/2 multiplet are evaluated along with a prediction for the magnitude and direction of the ground state magnetic moment. Our model correctly predicts that the moments order along the c axis but the observed magnetic moment of 0.405(5) mu_B is reduced compared to the predicted moment of 1.01 mu_B. This is ascribed to hybridization between the localized Ce^3+ f-electrons and the conduction band. This suggests that CeCoGe3 has a degree of hybridization between that of CeRhGe3 and the non-centrosymmetric superconductor CeRhSi3.

Structural and magnetic properties of quasi-one-dimensional doped LiCuVO4

The Neutron diffraction, X-ray photoemission and Magnetic properties of Zn, Co and Mn-doped LiCuVO4 were investigated. Both with Zn and Co doping the antiferromagnetic correlation increase. On the other hand Mn-doping induces the short range ferromagnetic ordering. Neutron diffraction study does not show any phase transition down to 5K i.e., there is no indication of long range magnetic ordering. Neutron diffraction study also indicates that with Zn, Co and Mn doping the V–O lengths are changed. Maximum change in the V–O distances is observed for Mn-doped sample. On the other hand, X-ray photoemission spectroscopic data indicates Mn doping converts some Cu2+ ions into Cu3+ ions.

Study of the structural, electric and magnetic properties of Mn-doped Bi2Te3 single crystals

Breaking the time reversal symmetry of a topological insulator, for example by the presence of magnetic ions, is a prerequisite for spin-based electronic applications in the future. In this regard Mn-doped Bi2Te3 is a prototypical example that merits a systematic investigation of its magnetic properties. Unfortunately, Mn doping is challenging in many host materials—resulting in structural or chemical inhomogeneities affecting the magnetic properties. Here, we present a systematic study of the structural, magnetic and magnetotransport properties of Mn-doped Bi2Te3 single crystals using complimentary experimental techniques. These materials exhibit a ferromagnetic phase that is very sensitive to the structural details, with TC varying between 9 and 13 K (bulk values) and a saturation moment that reaches 4.4(5) μB per Mn in the ordered phase. Muon spin rotation suggests that the magnetism is homogeneous throughout the sample. Furthermore, torque measurements in fields up to 33 T reveal an easy axis magnetic anisotropy perpendicular to the ab-plane. The electrical transport data show an anomaly around TC that is easily suppressed by an applied magnetic field, and also anisotropic behavior due to the spin-dependent scattering in relation to the alignment of the Mn magnetic moment. Hall measurements on different crystals established that these systems are n-doped with carrier concentrations of ∼ 0.5–3.0 × 1020 cm−3. X-ray magnetic circular dichroism (XMCD) at the Mn L2,3 edge at 1.8 K reveals a large spin magnetic moment of 4.3(3) μB/Mn, and a small orbital magnetic moment of 0.18(2) μB/Mn. The results also indicate a ground state of mixed d4–d5–d6 character of a localized electronic nature, similar to the diluted ferromagnetic semiconductor Ga1−xMnxAs. XMCD measurements in a field of 6 T give a transition point at T ≈ 16 K, which is ascribed to short range magnetic order induced by the magnetic field. In the ferromagnetic state the easy direction of magnetization is along the c-axis, in agreement with bulk magnetization measurements. This could lead to gap opening at the Dirac point, providing a means to control the surface electric transport, which is of great importance for applications.

Néel to spin-Peierls transition in a quasi-one-dimensional Heisenberg model coupled to bond phonons

The zero and finite temperature spin-Peierls transitions in a quasi-one-dimensional spin-$\frac{1}{2}$ Heisenberg model coupled to adiabatic bond phonons is investigated using the stochastic series expansion (SSE) quantum Monte Carlo (QMC) method. The quantum phase transition from a gapless N\'eel state to a spin-gapped Peierls state is studied in the parameter space spanned by spatial anisotropy, interchain coupling strength, and spin-lattice coupling strength. It is found that for any finite interchain coupling, the transition to a dimerized Peierls ground state only occurs when the spin-lattice coupling exceeds a finite, nonzero critical value. This is in contrast to the pure 1D model (zero interchain coupling), where adiabatic/classical phonons lead to a dimerized ground state for any nonzero spin-phonon interaction. The phase diagram in the parameter space shows that for a strong interchain coupling, the relation between the interchain coupling and the critical value of the spin-phonon interaction is linear whereas for weak interchain coupling, this behavior is found to have a natural logarithmlike relation. No region was found to have a long range magnetic order and dimerization occurring simultaneously. Instead, the N\'eel state order vanishes simultaneously with the setting in of the spin-Peierls state. For the thermal phase transition, a continuous heat capacity with a peak at the critical temperature ${T}_{c}$ shows a second order phase transition. The variation of the equilibrium bond length distortion ${\ensuremath{\delta}}_{eq}$ with temperature showed a power law relation which decayed to zero as the temperature was increased to ${T}_{c}$, indicating a continuous transition from the dimerized phase to a paramagnetic phase with uniform bond length and zero antiferromagnetic susceptibility.

Dome – like variation of the superconducting gap anisotropy in Fe-based superconductors

Experiments performed on different iron – based superconductors suggest a variety of possible structures of the superconducting energy gap, both nodeless and nodal. To understand the pairing mechanisms, it is important to identify common features in the behavior of different materials. Measurements of the temperature – dependent London penetration depth provide important information on the structure of the superconducting gap. We show that despite significant differences between different iron – based superconductors, there is a universal trend: the gap is least anisotropic at the optimal doping and its anisotropy increases upon the departure towards underdoped and overdoped ends of the "superconducting dome". This trend is not related to the presence of the long – range magnetic order in the underdoped state.

Structure and magnetic properties of Sr2CoRuO6

X-ray, neutron diffraction, magnetization, and resistivity measurements have been carried out on polycrystalline Sr2CoRuO6. It crystallizes with monoclinic cell in I2/c space group. In this structure Co and Ru are randomly distributed. AC magnetic susceptibility and dc magnetization exhibits a cusp and bifurcation of the ZFC and FC magnetization at the spin glass transition temperature ∼95K as against the expected ferromagnetic ordering due to Co3+ (t2g4 eg2)–O–Ru5+ (t2g3 eg0) interaction. The absence of enhancement in the intensity of the fundamental reflections and superlattice reflection in the neutron diffraction together with absence of neutron depolarization establishes that this compound lacks long range magnetic ordering and is a spin glass. A weak magnetoelastic coupling is observed in the form of an anomaly at the TSG in the temperature variation of bond lengths and angles. Resistivity measurement shows that Sr2CoRuO6 is a semiconductor with 3D Mott type VRH conduction mechanism.

Short-range magnetic order and effective suppression of superconductivity by manganese doping in LaFe1−xMnxAsO1−yFy

We present a study of the structural and physical properties of directly hole doped LaFe1-xMnxAsO (x = 0.0-0.2) and the influence of charge compensation / electron-doping by additional F doping in LaFe0.9Mn0.1AsO1-yFy (y = 0.1-0.5). High quality polycrystalline samples were prepared using a solid state metathesis reaction. The unit cell increases upon Mn doping, but decreases again when additional F is inserted. The semiconducting character of LaFe1-xMnxAsO decreases with additional F doping. Muon spin relaxation (muSR) measurements reveal short range magnetic order in LaFe1-xMnxAsO and a suppression of magnetism by additional electron-doping with fluoride in LaFe0.9Mn0.1AsO1-yFy. Superconductivity remains absent even though the electronic preconditions are fulfilled in electron-doped LaFe0.9Mn0.1AsO1-yFy at x > 0.1, which is suggestive of effective pair breaking by Mn in this system.

Spherical magnetic nanoparticles fabricated by laser target evaporation

Magnetic nanoparticles of iron oxide (MNPs) were prepared by the laser target evaporation technique (LTE). The main focus was on the fabrication of de-aggregated spherical maghemite MNPs with a narrow size distribution and enhanced effective magnetization. X-ray diffraction, transmission electron microscopy, magnetization and microwave absorption measurements were comparatively analyzed. The shape of the MNPs (mean diameter of 9 nm) was very close to being spherical. The lattice constant of the crystalline phase was substantially smaller than that of stoichiometric magnetite but larger than the lattice constant of maghemite. High value of Ms up to 300 K was established. The 300 K ferromagnetic resonance signal is a single line located at a field expected from spherical magnetic particles with negligible magnetic anisotropy. The maximum obtained concentration of water based ferrofluid was as high as 10g/l of magnetic material. In order to understand the temperature and field dependence of MNPs magnetization, we invoke the core-shell model. The nanoparticles is said to have a ferrimagnetic core (roughly 70 percent of the caliper size) while the shell consists of surface layers in which the spins are frozen having no long range magnetic order. The core-shell interactions were estimated in frame of random anisotropy model. The obtained assembly of de-aggregated nanoparticles is an example of magnetic nanofluid stable under ambient conditions even without an electrostatic stabilizer.