Paramagnetic Transition Research Articles

Effect of annealing temperature on structural, optical and magnetic properties of Cd1-xMnxZnO2 nanocomposites: An investigation for ferromagnetic

The structural, optical, and magnetic qualities of Cd1-xMnxZnO2 nanocomposites with (0.00 ≤ x ≤ 1.00) are investigated and the paramagnetic ferromagnetic transition is explained. Two series (effect of annealing and composition) were synthesized using the hydrothermal method and then annealed for 3 h at annealing temperatures (Tann) of 400 °C or 600 °C. It is found that an increase in either x or Tann correlates with significant change in unit cell volume (V), crystallite size (Dhkl), Debye temperature (θD) and energy gap (Eg). Further, the samples at x = 0.60 show a sudden change or inflection point in the behavior of these parameters is detected. Furthermore, the values of Eg and Dhkl for the x = 0.60 sample are independent of the chosen Tann. The weight percent of oxygen increased as x increased, as well as it was higher at 600 °C than at 400 °C. The value of Dhkl at x = 0.40 was increased by increasing Tann from 20.7 nm to 26.3 nm. Surprisingly, both series of samples exhibit weak paramagnetic properties as x increases to 0.40. However, increasing x to 0.60 yields a strong ferromagnetic signature for both series as well as unusual unsaturated magnetizations of 4.20 and 1.25 emu/g. However, with a larger further than of x above 0.60, the behavior returns to a strong paramagnetic behavior, but with a small percentage of residual hysteresis. These novel outcomes open the way for a possible mechanism for room temperature ferromagnetic (RTFM) and strongly recommend the use of Cd1-xMnxZnO2 nanocomposites, for magnetic imaging, and spintronic devices.

Structural, magnetic, magnetocaloric and critical studies of Sm-substituted La0.67-xSmxPb0.13Ca0.2MnO3 perovskite manganites

The structural, magnetic, magnetocaloric, and critical behaviors for Sm substituted La0.67-xSmxPb0.13Ca0.2MnO3 manganites with x = 0, 0.1, and 0.2 were investigated in this work. Based on Rietveld refinement of XRD patterns, all samples have an orthorhombic structure with the Pnma space group. With Sm substitution, the average ionic radii of A-site cation (<rA>), the unit cell volume (V), the Goldschmidt tolerance factor (tG), and the average <θMn-O-Mn> bond angle decrease. Whereas the average bond distance, <dMn-O>, and the variance disorder parameter (σ2) increase. Ferromagnetic (FM) to paramagnetic (PM) phase transitions with second-order type were revealed for all samples from magnetization measurements and Arrott plots. Curie temperature (TC) decreases with Sm substitution from 298 K for x = 0–256 K for x = 0.2. Large maximum entropy change and relative cooling power (6.20 J Kg−1 K−1 and 236 J Kg−1, respectively) have been observed for the undoped sample (x = 0), but the values of these parameters are suppressed due to the disorder caused by Sm doping. The estimated critical exponents (β, γ, and δ) for the x = 0 sample are consistent with tricritical mean-field theory. However, for x = 0.1 and 0.2, they are close to the 3D- Ising model. The change in this universality class can be associated with the increase of disorder by substituting the Sm3+ cations in La0.67-xSmxPb0.13Ca0.2MnO3 manganites.

Effects of Partial Manganese Substitution by Cobalt on the Physical Properties of Pr0.7Sr0.3Mn(1-x)CoxO3 (0 ≤ x ≤ 0.15) Manganites.

We have investigated the structural, magnetic, and electrical transport properties of Pr0.7 Sr0.3 Mn(1-x)Cox O3 nanopowders (x = 0, 0.05, 0.10 and 0.15). The Pechini Sol-gel method was used to synthesize these nanopowders. X-ray diffraction at room temperature shows that all the nano powders have an orthorhombic structure of Pnma space group crystallography. The average crystallite size of samples x = 0, 0.05, 0.10, and 0.15 are 33.78 nm, 29 nm, 33.61 nm, and 24.27 nm, respectively. Semi-quantitative chemical analysis by energy dispersive spectroscopy (EDS) confirms the expected stoichiometry of the sample. Magnetic measurements indicate that all samples show a ferromagnetic (FM) to paramagnetic (PM) transition with increasing temperature. The Curie temperature TC gradually decreases (300 K, 270 K, 250 K, and 235 K for x = 0, 0.05, 0.10, and 0.15, respectively) with increasing Co concentrations. The M-H curves for all compounds reveal the PM behavior at 300 K, while the FM behavior characterizes the magnetic hysteresis at low temperature (5 K). The electrical resistivity measurements show that all compounds exhibit metallic behavior at low temperature (T < Tρ) well fitted by the relation ρ = ρ0 + ρ2T2 + ρ4.5T4.5 and semiconductor behavior above Tρ (T > Tρ), for which the electronic transport can be explained by the variable range hopping model and the adiabatic small polaron hopping model. All samples have significant magnetoresistance (MR) values, even at room temperature. This presented research provides an innovative and practical approach to develop materials in several technological areas, such as ultra-high density magnetic recording and magneto resistive sensors.

Energy relaxation in (La0.6Pr0.4)0.7Ca0.3MnO3 films across the metal-insulator transition

The colossal magnetoresistive manganite ${({\mathrm{La}}_{0.6}{\mathrm{Pr}}_{0.4})}_{0.7}{\mathrm{Ca}}_{0.3}{\mathrm{MnO}}_{3}$ (LPCMO) undergoes a ferromagnetic (FM) metal to paramagnetic insulator phase transition at around 195 K, which develops via an intermediate polaronic state strongly susceptible to external magnetic fields. Transient reflectivity studies of LPCMO on timescales from sub-picoseconds to nanoseconds reveal that the overall system dynamics are strongly influenced by the phase transition with a sharp and strong decrease in the relaxation time while crossing from the ferromagnetic metallic phase into the paramagnetic insulating phase. We show that the long relaxation times of the reflectivity after nonequilibrium excitation within the FM phase are caused by the slow recovery of the ordered FM state after laser-induced demagnetization. Control of the nonequilibrium dynamics close to the phase transition is demonstrated by applying moderate magnetic fields below 1 T.

Effects of Fe doping on structure, negative thermal expansion, and magnetic properties of antiperovskite Mn3GaN compounds

AbstractWe synthesized antiperovskite Mn3Ga1−xFexN (0 ≤ x ≤ 0.30) compounds and investigated their negative thermal expansion (NTE) behavior, structure, and magnetic properties. A high‐resolution transmission electron microscopy analysis and a selected‐area electron diffraction (SAED) pattern indicate that the samples have high crystallinity with a single‐phase cubic structure. Tunable NTE behavior appears below room temperature, and the NTE operation temperature range (△T) is broadened while increasing the Fe doping. Furthermore, introducing Fe in Mn3Ga1−xFexN can efficiently adjust the NTE coefficient from −232.57 × 10−6/K (x = 0) to −12.57 × 10−6/K (x = 0.20), and the corresponding △T can be broadened from △T = 22 K to 51 K. Besides, the total entropy change (ΔStotal) at the phase transitions continuously decreases from 9.2 to 4.7 J/(kg K) while increasing the Fe content from x = 0.05 to 0.10. With increasing Fe into Ga sites, the magnetic ordering varies from antiferromagnetic (AFM) to ferromagnetic (FM), the AFM to paramagnetic (PM) phase transition temperature decreases, whereas the FM to PM transition temperature increases when increasing the Fe content. The present study indicates that magnetic element doping can efficiently tune the NTE and the correlated physical features of the antiperovskite compounds.

Magnetoelastic effect in R2Ni2In (R = Tb and Tm) investigated by neutron powder diffraction

ABSTRACT Magnetoelastic effect in R2Ni2In (R = Tb, Tm), associated with the antiferro- to paramagnetic phase transition at the Néel temperature TN equal to 40 K (R = Tb) or 4.8 K (R = Tm), has been investigated by neutron powder diffraction. Rietveld refinement reveals that the orthorhombic crystal structure, reported at room temperature, is stable down to low temperatures, including magnetically ordered state. Based on the diffraction data, thermal evolution of the lattice parameters a, b and c and the unit cell volume V have been determined. Both the lattice parameters as well as the unit cell volume show distinct jumps in the vicinity of the respective Néel temperatures, indicating presence of the magnetoelastic effect. The values of the lattice strains Δa, Δb, Δc and change of the unit cell volume ΔV, associated with the antiferro- to paramagnetic phase transition, are reported.

Impact of copper substitution on the magnetism and transport properties of La0.7Ba0.25Nd0.05Mn1−xCuxO3 (x = 0, 0.03, 0.05, and 0.07)

The impact of copper substitution on the structural, morphological, and magnetic properties, as well as the transport properties of La0.7Ba0.25Nd0.05Mn1−xCuxO3 (x = 0, 0.03, 0.05, and 0.07), has been investigated. Structural investigation results revealed that the samples crystallized in a rhombohedral system with the R3c space group without any detectable impurities. Morphological investigation showed that copper substitution significantly improved the grain size of the sample. Temperature dependence of magnetization measurement indicated that all samples underwent ferromagnetic to paramagnetic transition at the Curie temperature (TC). As copper concentration increased, the Curie temperature, TC, decreased from 302 K, 275 K, 258 K, and 229 K for samples with x = 0, 0.03, 0.05, and 0.07, respectively. Resistivity dependence on temperature measurement discovered that copper substitution significantly affected the overall resistivity of the samples. Additionally, copper substitution also induces a metal–insulator transition. The impact of copper substitution on the transport mechanism of the sample was investigated by fitting it with a suitable mathematical model.

Investigation of crystal structure and magnetic properties in magnetic composite of soft magnetic alloy and hard magnetic ferrite

The structural and magnetic properties have been investigated in the magnetic composites of hard magnetic Barium hexaferrite (BHF) and soft magnetic Ni–Mn–Sn Heusler alloy. The magnetic composites undergo two distinct ferromagnetic to paramagnetic and ferrimagnetic to paramagnetic phase transitions corresponding to alloy and BHF phases, respectively. Magnetic biasing between the hard and soft magnetic phases has been observed in the composites when both the phases are in the ferromagnetic ordering i.e., a squeezing in the magnetic hysteresis curve is observed around H = 0. The squeezing effect may be used in the magnetic memory device application where an optimum coercivity, high remanent magnetization, and high squareness ratio are required. On the other hand, the composites show high magnetocaloric effect with a constant high value of magnetic entropy changes between the two successive magnetic transitions. This gives an advantage with wide working temperature in the magnetocaloric application.

Температурно-барические особенности магнитных характеристик в системах со структурными переходами типа смещения

Using pnictides MnAs and germaindes Mn0.89Cr0.11NiGe as an example, the transformation of thermobaric features of their magnetic characteristics at high pressures is considered. A unified approach is used to describe paramagnetic (PM) structural transitions of the displacement type with a change in the symmetry PM(P63/mmc)-PM(Pnma) from hexagonal to orthorhombic. It is shown that the competition between the parameters of the structural and magnetic orders in both systems manifests itself differently in the stabilization and alternation of the so-called high-spin and low-spin magnetically ordered states initiated by pressure. As a consequence, the structural contribution in these systems weakens (MnAs) or enhances (Mn0.89Cr0.11NiGe ) the giant magnetocaloric effect in the temperature-baric region of the first-order magnetostructural phase transitions.

Magnetocaloric effect and critical behavior of the La0.75Ca0.1Na0.15MnO3 compound.

In this paper, we have studied the critical behavior and the magnetocaloric effect (MCE) simulation for the La0.75Ca0.1Na0.15MnO3 (LCNMO) compound at the second order ferromagnetic-paramagnetic phase transition. The optimized critical exponents, based on the Kouvel-Fisher method, were found to be: β = 0.48 and γ = 1. These obtained values supposed that the Mean Field Model (MFM) is the proper model to analyze adequately the MCE in the LCNMO sample. The isothermal magnetization M(H, T) and the magnetic entropy change -ΔSM(H, T) curves were successfully simulated using three models, namely the Arrott-Noakes equation (ANE) of state, Landau theory, and MFM. The framework of the MFM allows us to estimate magnetic entropy variation in a wide temperature range within the thermodynamics of the model and without using the usual numerical integration of Maxwell relation.

Temperature-baric features of magnetic characteristics in systems with structural transitions of the displacement type

Using pnictides MnAs and germaindes Mn0.89Cr0.11NiGe as an example, the transformation of thermobaric features of their magnetic characteristics at high pressures is considered. A unified approach is used to describe paramagnetic (PM) structural transitions of the displacement type with a change in the symmetry PM(P6_3/mmc)-PM(Pnma) from hexagonal to orthorhombic. It is shown that the competition between the parameters of the structural and magnetic orders in both systems manifests itself differently in the stabilization and alternation of the so-called high-spin and low-spin magnetically ordered states initiated by pressure. As a consequence, the structural contribution in these systems weakens (MnAs) or enhances Mn0.89Cr0.11NiGe the giant magnetocaloric effect in the temperature-baric region of the first-order magnetostructural phase transitions. Keywords: structural phase transitions of the displacement type, magnetostructural phase transitions, helimagnetism, ferromagnetism, high spin-low spin states, direct magnetocaloric effect.

Nitrogen vacancy defects in single-particle nanodiamonds sense paramagnetic transition metal spin noise from nanoparticles on a transmission electron microscopy grid.

Spin-active nanomaterials play a vital role in current and upcoming quantum technologies, such as spintronics, data storage and computing. To advance the design and application of these materials, methods to link size, shape, structure, and chemical composition with functional magnetic properties at the nanoscale level are needed. In this work, we combine the power of two local probes, namely, Nitrogen Vacancy (NV) spin-active defects in diamond and an electron beam, within experimental platforms used in electron microscopy. Negatively charged NVs within fluorescent nanodiamond (FND) particles are used to sense the local paramagnetic environment of Rb0.5Co1.3[Fe(CN)6]·3.7H2O nanoparticles (NPs), a Prussian blue analogue (PBA), as a function of FND-PBA distance (order of 10 nm) and local PBA concentration. We demonstrate perturbation of NV spins by proximal electron spins of transition metals within NPs, as detected by changes in the photoluminescence (PL) of NVs. Workflows are reported and demonstrated that employ a Transmission Electron Microscope (TEM) finder grid to spatially correlate functional and structural features of the same unique NP studied using NV sensing, based on a combination of Optically Detected Magnetic Resonance (ODMR) and Magnetic Modulation (MM) of NV PL, within TEM imaging modalities. Significantly, spin-spin dipole interactions were detected between NVs in a single FND and paramagnetic metal centre spin fluctuations in NPs through a carbon film barrier of 13 nm thickness, evidenced by TEM tilt series imaging and Electron Energy-Loss Spectroscopy (EELS), opening new avenues to sense magnetic materials encapsulated in or between thin-layered nanostructures. The measurement strategies reported herein provide a pathway towards solid-state quantitative NV sensing with atomic-scale theoretical spatial resolution, critical to the development of quantum technologies, such as memory storage and molecular switching nanodevices.

P-type semiconductor Gd/Fe ion doped Ni-Mg nanoferrites applications

Citrate gel-auto combustion was used to create gadolinium doped Ni-Mg ferrites with the chemical formula Ni0.8Mg0.2GdxFe2-xO4 (NMGF) with compositions x = (0.00, 0.005, 0.010, 0.015, 0.020, and 0.025). Gadolinium substitution has been studied to see how it affects the structural and electrical characteristics of Ni-Mg complexes. The NMGF crystallizes into a cubic spinel structure, with no secondary phase emerging, according to X-ray diffraction patterns. The elemental composition analysis validates the existence of the predicted components in the samples based on stoichiometry. Images taken with a transmission electron microscope with high resolution and a scanning electron microscope indicate the type of grain formation as well as the particle size of the produced materials. As compared to undoped Ni-Mg ferrite, Fourier transform infrared spectroscopy verifies the establishment of spinel phase and predicts the movement of bands corresponding to Fe-O vibrations towards higher wavenumbers. The samples were measured for conductivity at temperatures ranging from 300 to 723 K. Conductivity measurements revealed the ferromagnetic to paramagnetic transition temperature (Tc) for all materials. The activation energy was determined below and above Tc. TEP measurements of NMGF ferrites were made using a differential technique at temperatures ranging from 300 to 723 K. The prepared ferrites' Seebeck coefficient (S) rose with increasing temperature.

Theoretical aspects of magnetic, magnetocaloric, and critical exponents: Nanomaterial model

In this present research paper, our focus was on studying the nanomaterial model with the spin vector and its amplitude was 5/2: the magnetic, magnetocaloric effect and the critical exponents. By using Monte Carlo method, I succeeded in determining the fact that the magnetic transition nature was second-order with the Curie temperature of TC = 14.46 K. The maximum magnetic entropy change (of) (ΔSM) of 3.53 J kg-1K−1, the large Relative Cooling Power (RCP) of 32.67 J kg−1 and the corresponding maximum Refrigeration Capacity (RC) of 24.50 J kg−1 were established under the magnetic field of 8 T. The critical exponents were determined with the purpose of studying the nature and underlying mechanism of the Ferromagnetic (FM) to the Paramagnetic (PM) phase transition. The critical exponents were obtained using magnetocaloric data from the field dependence of the magnetic entropy, the relative cooling power and Widom scaling relation. β, γ and δ indicated that the nanomaterial model belonged to the two-dimensional (2D)-Ising model with long-range interaction.

Pressure effect on the structural, magnetic and thermophysical properties of X12Cr13 martensitic stainless steel prepared by powder metallurgy method

Low carbon (C: 0.03-0.15%) and high Cr contents (Cr: 11-15%) martensitic stainless steel (MSS) is widely used for industrial applications due to its good mechanical properties and corrosion resistance. In this study, we investigated the pressure effect on the structural, magnetic and thermophysical properties of X12Cr13 MSS which was compacted using powder metallurgy method under 400 and 600 MPa pressures and sintered at 1200 °C temperature for an hour under Ar atmosphere. Pressing and sintering processes resulted in increased density of microstructures from 5.84 g/cm 3 to 6.12 g/cm 3 , decreased porosity from 7.58% to 3.39%, increased hardness from 93.24 HB to 110.09 HB (N/ mm 2 ) and decreased carbide particles from 2.65% to 2.13 wt% in the structures. We observed α -Fe, γ -Fe and M 23 C 6 (M: Cr or Fe) phase formations in the structure due to the applied pressure and the sintering process. The magnetic properties of these steels have been investigated as a function of temperature between 300-400 K and applied magnetic field of ±4 T. We observed improved magnetic properties with increasing pressure, and ferromagnetic to paramagnetic phase transition occurred from 300 K to 400 K. While maximum saturation magnetization is found to be 70 emu/g at 300 K for 600 MPa sample, maximum magnetic susceptibility and permeability for 600 MPa sintered sample are recorded as 17.13 and 1.08 m 3 /kg, respectively. Also, the maximum specific heat capacity and enthalpy are recorded as 1.85 J/g °C and 536.05 J/g (at 579 °C temperature) on the sample compacted on the 600 MPa pressure, respectively. • X12Cr13 MSS samples were prepared by P/M method at 400 MPa and 600 MPa. • 600 MPa pressing and 1200 °C sintering enhanced physical and magnetic properties • MSS prepared at 600 MPa exhibits 110.09 HB hardness and 6.12 g/cm 3 density. • The maximum saturation magnetization found to be 70 emu/g at RT for 600 MPa sample. • The 600 MPa sample provided 536.0 J/g heat storage capacity at 579°C.

Mechanical ordering of pigment crystallites in oil binder: can electron paramagnetic resonance reveal the gesture of an artist?

Is it possible to reconstruct the gesture of an ancient artist applying a paint layer, considering that the orientation distribution of crystallites of an inorganic pigment remains definitively imprinted on the support after drying of the layer? If the pigment contains paramagnetic transition metal ions whose magnetic interactions are themselves anisotropic, then the shape of the electron paramagnetic resonance (EPR) spectrum should reflect the distribution of grain orientations. We have demonstrated this effect in the case of Egyptian blue CaCuSiO, a pigment used for at least 3 millennia in antiquity, by reconstructing the probability density of crystallite orientations under various modes of application, such as brush painting, dabbing and droplet deposition.

Room-temperature antiferromagnetic order in monolayer Fe2C

We have studied the room-temperature long-range antiferromagnetic order in the ${\mathrm{Fe}}_{2}\mathrm{C}$ monolayer using the combination of first-principles calculations and the Green's function analysis within the anisotropic Heisenberg model. The ${\mathrm{Fe}}_{2}\mathrm{C}$ monolayer is a semimetal with the out-of-plane antiferromagnetic order between two $\mathrm{Fe}$ planes. The Green's function approach within the random phase approximation is formulated to calculate the temperature-dependent antiferromagnetic magnon energy and the spin correlation function in a two-dimensional antiferromagnetic monolayer. The correlation function is used to evaluate the sublattice magnetization and study the magnetic phase transition in monolayer ${\mathrm{Fe}}_{2}\mathrm{C}$. Moreover, the spin Hamiltonian and the Green's function formalism are developed to investigate the antiferromagnetic ${\mathrm{Fe}}_{2}\mathrm{C}$ monolayer in the presence of an external magnetic field applied along the easy axis. The H-T phase diagram shows that the antiferromagnetic to spin-flop and the spin-flop to paramagnetic phase transitions occur in low temperatures. Finally, we estimate the N\'eel temperature and the critical values of the magnetic field strength for these two phase transitions.

Structure, magnetic and magnetocaloric properties of polycrystalline Er3AlC compound

The development of magnetic materials with large magnetocaloric effects for solid state refrigeration technology is receiving increasing attention. In this work, the crystal structure, magnetic and magnetocaloric properties of polycrystalline Er3AlC compound are investigated. Powder X-ray diffraction indicate that Er3AlC crystallizes in the inverse perovskite structure, belonging to the space group Pm3¯m(221). The polycrystalline sample exhibits two successive magnetic transitions: antiferromagnetic-ferromagnetic below 2 K and ferromagnetic–paramagnetic transition around 4.1 K. The value of the maximum magnetic entropy changes are 13.9 J/kg K and 30.5 J/kg K under the field changes of 0–2 T and 0–5 T, respectively. The large magnetic entropy change under low fields makes Er3AlC compound a potential candidate for cryogenic magnetic refrigeration.

Peculiar temperature dependence of magneto-optic Kerr rotation associated with antiferromagnetic–paramagnetic transition

We investigate the magneto-optic Kerr effect in perpendicularly magnetized Pt/Co/Ir/Cr2O3/Pt thin films, associated with the antiferromagnetic–paramagnetic transition of the Cr2O3 layer. The magneto-optic Kerr rotation angle (θ K) shows oscillatory behavior as a function of the photon energy of incident light owing to interference in the Cr2O3 layer. The temperature dependence of θ K at 2.67 eV (λ = 465 nm), at which the largest θ K is obtained, shows a sharp dip at 287.0 K. The dip temperature is similar to the reported Néel temperature for Cr2O3 thin films. Although the θ K spectra measured at several temperatures are generally explained by the classical interference model, θ K is enhanced at 2.36–2.79 eV (λ = 525–445 nm) close to the dip temperature. This peculiar enhancement in θ K is discussed on the basis of the anomaly in the optical parameters of the Cr2O3 layer associated with the antiferromagnetic–paramagnetic transition.

Superior La0.67K0.33-xSrxMnO3 films with room-temperature TCR prepared by spin coating method

La0.67K0.33-xSrxMnO3 thin films were grown on LaAlO3 (010) substrates via sol–gel and spin coating methods. The replacement of K ions with Sr ions affected the eg electron bandwidth and concentration of Mn3+/Mn4+ pairs as well as effectively modulated the magnetic/orbital order and lattice structure. Consequently, the ferromagnetic metal to paramagnetic insulation transition was affected, which further optimized the resistivity, temperature coefficient of resistivity (TCR), peak TCR temperature (TK), and peak resistivity temperature (TP). At temperatures below 230 K, temperature-independent scattering and electron-electron scattering were practically not observed in the films. Overall, electrical properties of films improved with an increase in the Sr doping content. The superior La0.67K0.27Sr0.06MnO3 film exhibited a maximum TCR of 11.88% K−1 (298.3 K), which is approximately 31% higher than that of bulk ceramic with the same composition. The as-developed films exhibit significant potential for application in uncooled infrared bolometers.