Ferro-paramagnetic Transition Research Articles

Enhancing future technologies: Sol-Gel synthesis of Sr0.6Ag0.4MnO3 manganite perovskite

The research successfully produced Sr0.6Ag0.4MnO3, a silver strontium manganite with the desired perovskite crystal structure, using the sol-gel technique. Extensive analysis revealed its notable characteristics, indicating potential uses across various fields. X-ray diffraction showed the compound's tetragonal structure at room temperature, affirming its stability. Morphological and chemical assessments confirmed the material's consistency and evenness, with crystallites averaging 27 nm (from XRD) and 90 nm (from SEM). The material displayed a ferro-paramagnetic transition at 375 K, suggesting suitability for magnetic applications, alongside a slight drop in electrical resistance under a magnetic field, hinting at potential magnetoresistive properties for electronic devices. In terms of dielectric properties, particularly at low frequencies, the material demonstrated a high dielectric constant and low tangent loss, indicating its potential for electrical components. Overall, these findings position Sr0.6Ag0.4MnO3 as a versatile material with promising applications in magnetism, electronics, and electrical components.

Cu-mediated grain boundary engineering in Nd–Ce–Fe–B nanostructured permanent magnets

Grain boundary (GB) engineering is of general significance for developing high-performance permanent magnets (PMs), but remains largely lacking in Nd–Ce–Fe–B nanostructured PMs containing the novel REFe2 (1:2, RE = rare earth) phase, previously considered as a coercivity-damaging agglomerated paramagnetic precipitate. Here we present a Cu-mediated GB engineering strategy that delicately controls the composition, distribution and magnetism of the 1:2 phase in (Nd0.5Ce0.5)30.5Fe68.5-xCuxB1.0 nanostructured magnets (x = 0–0.5). Experimental studies show that the incorporated Cu enables the formation of a continuous 1:2 GB phase, which is reported for the first time in Nd–Ce–Fe–B nanostructured magnets. More interestingly, the Cu infiltration into the 1:2 phase also permits more Nd to replace Ce, generating a novel Nd-dominated 1:2 phase with a ferro-paramagnetic transformation. A certain fraction of the 1:2 phase with ferromagnetic nature results in an obvious kink near −35 kA/m reversal field at 300 K, which disappears after the ferro-paramagnetic transition at 350 K. At optimal Cu doping (x = 0.2) with a maximized coercivity of 992 kA/m, the paramagnetic and ferromagnetic 1:2 phases coexist with highest total fraction of 4.8 wt%, revealing an advantageous role of paramagnetic 1:2 GB phase in enhancing coercivity. Our exploration paves a novel Cu-mediated approach for rational engineering of the 1:2 GB phase, which may exert far-reaching significance for developing low-cost Nd–Ce–Fe–B PMs.

Internal friction phenomena in a wide temperature range up to 800°C in long-term annealed Fe-(0−30) at% Ga alloys

The internal friction (IF) phenomena were systematically studied in a temperature range from room temperature (RT) to 800 °C for Fe-(0−30) at% Ga alloys annealed at 480 °C for 14 days, which include the magnetic-related high damping plateau (HDP) and the point of ferro-paramagnetic transition (Tc), grain boundary relaxations, Zener relaxations, and the IF peaks associated with phase transitions. It was found that the rapid decay temperature of the HDP decreases with increasing Ga content, which is consistent with the variation of the Curie point (Tc), and the HDP disappears when the Ga content is greater than 18 at%. In the long-term annealed Fe-30at%Ga alloy, a frequency-independent phase transition IF peak was observed and its mechanism was suggested as the phase transition of L12→A2/B2. The phase transitions in Fe-(0–30 at%)Ga alloys evaluated by the IF technique are in good agreement with the equilibrium phase diagram. In addition, a new relaxation peak was observed before the displacive phase transitions of L12→D019 and L12→A2/B2, and its mechanism could be related to Zener relaxation in the FCC structured L12 phase.

Thermo-magnetic characterization of phase transitions in a Ni-Mn-In metamagnetic shape memory alloy

The partially overlapped ferroelastic/martensitic and para-ferromagnetic phase transitions of a Ni50.53Mn33.65In15.82 metamagnetic shape memory alloy have been studied from calorimetric, magnetic and acoustic emission measurement. We have taken advantage of the existence of thermal hysteresis of the first order ferroelastic/martensitic phase transition (~2.5 K) to discriminate the latent heat contribution ΔHt=7.2115 kJkg-1 and the specific heat contribution ΔHc=2161 Jkg-1to the total excess enthalpy of the phase transition. The specific heat was found to follow a step-like behavior at this phase transition. The intermittent dynamics of the ferroelastic/martensitic transition has been characterized as a series of avalaches detected both from acoustic emission and calorimetric measurements. The energy distribution of these avalanche events was found to follow a power law with a characteristic energy exponent ε≅2 which is in agreement with the expected value for a system undergoing a symmetry change from cubic to monoclinic. Finally, the critical behavior of the para-ferromagnetic austenite phase transition that takes place at ~311 K has been studied from the behavior of the specific heat. A critical exponent α≅0.09 has been obtained, which has been shown to be in agreement with previous values reported for Ni-Mn-Ga alloys but different from the critical divergence reported for pure Ni.

Structural and magnetic properties of Sc1-xNbxFe2 intermetallics showing anomalous zero thermal expansion

Ternary intermetallics deriving from ScFe2 Laves phases can present a relatively unique case of ferro-ferromagnetic transition originating from an iron moment instability, which is potentially interesting for several applications. Yet, at the exception of (Sc,Ti)Fe2, their structural and magnetic phase diagrams remain scarcely explored. Here, we present a systematic investigation of the crystal structure and magnetic properties of Sc1-xNbxFe2 intermetallics. This series is found to mostly crystallize in the C14 hexagonal structure. But, in contrast to former studies, a C14/C15 hexagonal/cubic dimorphism is observed for the binary parent ScFe2, with the C15 structure that can be brought to the edge of stability depending on heat treatments. This led us to revisit the properties of ScFe2 via first-principles calculations. The total energy difference between C14 (stable) and C15 structures is found small, and C15 ScFe2 is predicted to be ferromagnetic with a saturation magnetization close to that of C14 ScFe2, which is fully compatible with experimental observations. Experimentally, Sc1-xNbxFe2 intermetallics with x ≤ 0.35 are ferromagnetic with Curie temperatures decreasing with increasing the Nb content; while such a long range ferromagnetic order with net magnetization is no longer observed for x > 0.6. A Néel transition is observed around 250 K in 0.6 ≤ x ≤ 0.9 alloys, this antiferromagnetic order is coexisting with a minor ferromagnetic phase, in line with former results from Mössbauer spectroscopy. For 0.2 ≤ x ≤ 0.3 samples, an ─unusual─ ferro.-ferromagnetic transition with a change in magnetization from ~1.2 μB/Fe to ~0.9 μB/Fe upon heating is found around 150 K in addition to the ferro-paramagnetic transition. This broad ferro.-ferromagnetic transition is isostructural as the C14 hexagonal crystal structure is preserved, but it leads to a virtually zero thermal expansion up to 250 K.

Elastic backbone phase transition in the Ising model.

The two-dimensional (zero magnetic field) Ising model is known to undergo a second-order paraferromagnetic phase transition, which is accompanied by a correlated percolation transition for the Fortuin-Kasteleyn (FK) clusters. In this paper we uncover that there exists also a second temperature T_{eb}<T_{c} at which the elastic backbone of FK clusters undergoes a second-order phase transition to a dense phase. The corresponding universality class, which is characterized by determining various percolation exponents, is shown to be completely different from directed percolation, which leads us to propose a new anisotropic universality class with β=0.54±0.02, ν_{||}=1.86±0.01, ν_{⊥}=1.21±0.04, and d_{f}=1.53±0.03. All tested hyperscaling relations are shown to be valid.

Flat-band ferromagnetism of SU(N) Hubbard model on Tasaki lattices

We investigate the para-ferro magnetic transition of the repulsive SU(N) Hubbard model on a type of one- and two-dimensional decorated cubic lattices, referred as Tasaki lattices, which feature massive single-particle ground state degeneracy. Under certain restrictions for constructing localized many-particle ground states of flat-band ferromagnetism, the quantum model of strongly correlated electrons is mapped to a classical statistical geometric site-percolation problem, where the nontrivial weights of different configurations must be considered. We prove rigorously the existence of para-ferro transition for the SU(N) Hubbard model on one-dimensional Tasaki lattice and determine the critical density by the transfer-matrix method. In two dimensions, we numerically investigate the phase transition of SU(3), SU(4) and SU(10) Hubbard models by Metropolis Monte Carlo simulation. We find that the critical density exceeds that of standard percolation, and increases with spin degrees of freedom, implying that the effective repulsive interaction becomes stronger for larger N. We further rigorously prove the existence of flat-band ferromagnetism of the SU(N) Hubbard model when the number of particles equals to the degeneracy of the lowest band in the single-particle energy spectrum.

Tuning the magnetic and magnetocaloric properties of austenitic Ni-Mn-(In,Sn) Heuslers

In this work, we highlight the occurrence of different physical mechanisms that independently control the saturation magnetization and the ferro-paramagnetic transition temperature of Ni-Mn-based Heusler compounds, opening new possibilities in mastering the functional properties of this wide class of magnetic materials. We present the magnetic, structural and magnetocaloric features of a complete Ni48Mn36In16−xSnx (x = 0–16) series. The observed different trends of the critical temperature and of the saturation magnetization on varying the Sn to In ratio are discussed with the help of first-principles calculations of the electronic structure and magnetic interactions of the compound.

Microstructure and magnetocaloric effects of Mn1.2Fe0.8P0.6Si0.4B0.05 alloys prepared by ball milling and spinning methods

Abstract The Mn1.2Fe0.8P0.6Si0.4B0.05 alloys were prepared by ball milling and melt-spinning methods. The structure and magnetic characteristics of all samples were examined by X-ray diffraction, vibrating sample magnetometer and SEM. Results show that both the ribbon and bulk alloys can crystallize in a hexagonal Fe2P-type phase with some impurity phase. The lattice parameters, a and c, of Fe2P-type phase are 6.02960 A, 6.03033 A, and 3.42310 A, 3.44431 A for ribbon and bulk Mn1.2Fe0.8P0.6Si0.4B0.05 alloys, respectively. The Curie temperature increased by 20% from 165 K in bulk to 197 K in ribbon while thermal hysteresis and magnetic hysteresis decreased by 28% and 80% for ribbon sample, respectively. Moreover, the values of magnetic entropy change can be tuned from 15.7 J⋅kg−1⋅K−1 in bulk to 21.8 J⋅kg−1⋅K−1 in ribbon under 0–5 T, resulting in the effective refrigerant capacity (RCE) increasing from 238 to 286 J⋅kg−1. The nature of the phase transitions was studied through the Arrott plots, indicating that the samples undergo first-order ferro-paramagnetic phase transitions. The origin of magnetic hysteresis losses is also discussed deeply. Furthermore, this alloys with large magnetic entropy change could be an interest potential for future magnetic refrigeration applications.

Critical behavior of CrTe1-xSbx ferromagnet

The modified Arrott plots and Kouvel-Fisher analysis are used to investigate the critical behavior of CrTe1-xSbx ferromagnetic material near its transition temperature Tc. The Ferro–Paramagnetic transition is found to be a second-order phase transition. For x=0.2, the critical exponents closely follow the Mean Field Model with the estimated values of the exponents: β=0.60±0.03, γ=1.00±0.03 and δ=2.67±0.03. We also found with increasing Sb-concentrations, the critical exponents significantly deviate from the mean field values and gradually shift towards the 3-Dimensional behavior. The deviation may indicate changes in the spin configuration with increasing Sb concentrations.

Effect of Annealing on the Curie Temperature in the Bulk Amorphous Alloys

The paper presents results of research for volumetric amorphous alloys Fe61+xCo10-XY8W1B20 where x = 0,12 in the shape of plater of 10mm x 5mm x 0.5mm diameter. Amorphous Samales were annealed at 953K for 10 minutes what caused their partial crystallization. As a result of the thermal interference in the volume of alloys, three different crystalline phases were formed aFe, Fe5Y and Fe3B. For samples after solidification and after thermal treatment thermomagnetic studiem were conducted. For amorphous alloys, only one ferro-paramagnetic transition was visible, and for the alloys after the isothermal annealing process there were two inflections on the curve .m0Ms (T) corresponding to the two Curie temperatures. These intersections came from two amorphous phases. As a result of the research, it was found that these alloys crystallized in the primal crystalization. Crystallization was the reason for the increase of the first Curie temperature of the amorphous matrix while retaining its decrease with cobalt additive. The value of the second Curie temperature in the alloys after heating was found to depend mainly on the size of the crystallization products and in particular on the Fe5Y crystallite size.

Large magnetic entropy change and magnetic phase transitions in rapidly quenched bulk Mn-Fe-P-Si alloys

Mn1.15Fe0.85P0.50Si0.45B0.05 alloys were prepared by copper mold suction casting method. Subsequent annealing processes were employed to tune the microstructures and magnetocaloric effects. Results show that Mn1.15Fe0.85P0.50Si0.45B0.05 alloys crystallize in a hexagonal phase with the Fe2P structure type. With increasing annealing temperature, the lattice parameters of a and c of Fe2P-type phase increase from 5.7988(1)Å to 6.0785(2)Å and from 3.3218(1)Å to 3.4727(2)Å for the Mn1.15Fe0.85P0.50Si0.45B0.05 alloys according to XRD. At the same time the Curie temperature and magnetic entropy change increase from 233 K to 244 K and from 8.8 J kg−1K−1 to 17.0 J kg−1K−1 (ΔH = 2 T), respectively, while the thermal hysteresis decreases. The entropy changes of these alloys are also estimated from the Clausius-Clapeyron equation, Landau theory and heat capacity, respectively. The nature of the phase transitions were studied through the Arrott plots, which indicate that the samples undergo first-order ferro-paramagnetic phase transitions. However, the universal curve of scaled magnetic entropy change reveals that during the magnetic phase transition, there exists a critical magnetic field, about 1.25 T, below which the sample undergoes a second-order phase transition and above which it displays a first-order phase transition. Furthermore, mechanisms for the large magnetic entropy change and possibilities for the room-temperature magnetic refrigeration are discussed.

Effect of manganese doping on vibrational and physical properties of ZrTe 3 O 8

The powder sample of xMnO2–(1−x) ZrTe3O8 (x = 7%) was prepared by the conventional solid state reaction method. X-ray diffraction showed that the compound crystallized at room temperature in the cubic fluorite structure (in a cubic unit-cell Ia3¯ as MTe3O8-type framework) with lattice parameter a = 11.3298(2) Ǻ. The structure was built up of TeO4E (E = Electronic lone pair of Te(IV)) disphnoids and regular ZrO6 octahedra. The crystal structure cohesion was ensured via TeO(2)Zr and TeO(1)Te bridges. The Raman spectrum was dominated by a stronger band at 858 cm−1, characteristic of TeO(2)Zr bridges asymmetric stretching vibration. Thus, the TeO(2) and Zr(Mn)O(2) bonds are chemically inequivalent and then the TeO(2)Zr bridges are chemically asymmetric. Magnetization measurements versus temperature in an applied magnetic field of 0.05 T were determined. The doping of Zr by Mn induces a ferro-paramagnetic transition at T = 18.5 K. The complex impedance of the xMnO2-(1−x) ZrTe3O8 (x = 7%) ceramics has been investigated in the temperature range 293–843 K and in the frequency range 100 Hz–1 MHz. Dielectric data were analyzed using complex permittivity (ε′), (ε″) and tan (δ) for the sample at various temperatures. The conductivity follows the Arrhenius relation.

Effect of temperature and magnetic field on magnetomechanical damping of Fe-based bulk metallic glasses

Temperature and magnetic field dependence of magnetomechanical damping (MMD) of two ferromagnetic Fe-based bulk metallic glasses with different Curie temperatures, TC, have been studied over a broad temperature interval from the para-ferromagnetic transition down to 15 K. The damping has been scanned under periodic magnetic field at certain preselected temperatures in the ferromagnetic and paramagnetic phases. The selection of bulk metallic glasses for investigations allowed us to eliminate all dislocation-related anelastic effects and facilitated separation of the MMD components. Under zero field, the non-linear MMD emerges at TC and first increases linearly with (TC − T), then levels off until a maximum is formed at around 36 K. At lower temperatures, the magnetic domain wall related non-linear MMD component is partially or completely supressed, depending on the alloy composition. Qualitatively similar anomaly is found in the temperature dependence of the linear macroeddy current damping. These anomalies in the temperature spectra are concomitant with the emergence of a notable hysteresis in MMD versus periodic field dependences and of a maximum of non-linear MMD close to the position of the macroeddy damping peak. The uncovered phenomena are attributed to abrupt change of magnetic properties of ferromagnetic bulk metallic glasses at low temperatures, presumably due to the re-entrant spin glass transition.

Synthesis, crystal structure determination, thermal and magnetic properties of the new Cu0.73Ni0.27(HSeO3)2 compound

A novel three-dimensional Cu0.73Ni0.27(HSeO3)2 compound was prepared from an aqueous solution. This compound crystallizes in the monoclinic system with P21/n space group and with the following cell parameters: a=6.4379(3)Å; b=7.3555(3)Å; c=5.7522(3)Å; β=93.4341(1)°; V=271.90(2)Å3 and Z=2. The reported material has been structurally characterized by X-ray powder diffraction and confirmed by scanning electron microscope and energy dispersive spectroscopy (MEB/EDS) analysis. The copper/nickel atom is surrounded by an octahedron coordination of oxygen atoms from sex hydrogenoselenites anions. The presence of (HSeO3)− has been further confirmed by IR spectroscopy and this compound exhibits a phase transition at 356K, this transition has been detected by differential scanning calorimetry and TG-DTA measurement. The magnetic property of this material was determined. The ferromagnetic ordering is further confirmed by the magnetic field dependence of the magnetization (Hysteresis loop) at 10K. The substitution of Cu by Ni induces a ferro-paramagnetic transition at T=31K. Field cooled (FC) and Zero field cooled (ZFC) magnetization measurements under an applied field of 100Oe in the temperature range of 10–300K were performed. These measurements have been resulted the blocking temperature (TB) at around 25K.

Synthesis, Phase Transition of La0.69Sr0.31MnO3 Nanoperovskites Toward Its Versatile Structural, Electrical and Mechanical Properties Employing Ultrasonic Measurements

The present investigation correlates the propagation of ultrasonic waves with various micro structural features of nano La0.69Sr0.31MnO3 (LSMO) perovskites with different grain sizes. A solid state reaction followed by the ball milling technique was used to synthesize the nano LSMO perovskite samples with various grain sizes. The occurrence of ferro-paramagnetic transition temperature (Tc) was explored through the observed anomalous behaviour in ultrasonic velocities, attenuations and elastic moduli. As the particle size gets reduced, lower Tc and broader transitions are observed due to the distribution of grain boundaries. The diffusion of the FM–PM phase transition along with decrease in Tc is correlated due to the effect of particle size. Furthermore structural, vibrational and electrical properties of nanosized LSMO perovskite samples with different grain sizes were studied by XRD, FTIR, BET surface area measurement, HRSEM, TEM and four probe conductivity studies. The phase of the synthesized nano LSMO perovskite samples are perfectly indexed to pure rhombohedral perovskite type crystal structure. The conductivity study proves the semiconductor nature of the nano LSMO perovskite samples. In addition to this, the peak broadening in ultrasonic studies at phase transition is in line with the observation made from the XRD pattern for the prepared nano LSMO perovskite samples.

Noise-induced absorbing phase transition in a model of opinion formation

In this work we study a 3-state (+1, −1, 0) opinion model in the presence of noise and disorder. We consider pairwise competitive interactions, with a fraction p of those interactions being negative (disorder). Moreover, there is a noise q that represents the probability of an individual spontaneously change his opinion to the neutral state. Our aim is to study how the increase/decrease of the fraction of neutral agents affects the critical behavior of the system and the evolution of opinions. We derive analytical expressions for the order parameter of the model, as well as for the stationary fraction of each opinion, and we show that there are distinct phase transitions. One is the usual ferro–paramagnetic transition, that is in the Ising universality class. In addition, there are para-absorbing and ferro-absorbing transitions, presenting the directed percolation universality class. Our results are complemented by numerical simulations.

Unified theoretical approach for binary and ternary alloys via an effective field theory

Abstract We describe the phase diagram of binary and ternary disordered alloys using the mixed-bond Ising model, via effective field theory (EFT). For example, we describe the Fe–Al alloy as a mixed-bond system instead of as diluted alloy. In our approach, we obtain the percolation threshold for some lattices and describe the lines of ferro-paramagnetic transition of Fe–Al, Fe–Mn, Fe–Mn–Al and Fe–Ni–Mn alloys and we obtain good agreement with the experimental data.

Effect of yttrium substitution on the electrical and magnetic properties of La0.7Ba0.3MnO3 compound

In the recent years manganese oxides La0.7A0.3MnO3 (A=Ca, Sr and Ba) received great attention because of their unique electrical and magnetic properties. Colossal changes in the magneto resistance upto the order of 106–108 have been observed in thin films, single crystals and bulk materials. We have studied the effect of Yttrium substitution on the electrical and magnetic properties of La0.7Ba0.3MnO3 compound. Samples of the composition La0.7−xYx Ba0.3MnO3 with x=0.0–0.4 were prepared using solid state reaction method. XRD patterns of these samples show the single phase nature of the samples. Electrical resistance of samples was measured in the presence of zero and various applied magnetic fields. All the samples have shown a metal–insulator transition and Yttrium substitution has resulted in a systematic decrease in this transition temperature TMI. Magneto resistance of samples was also found to increase with Yttrium substitution. Susceptibility measurements on these samples have indicated a ferro-paramagnetic transition. The results are discussed in terms of size effects and changes in Mn3+–O–Mn4+ bond angle.

Structural, electrical and dielectric properties of La0.7Sr0.3MnO3–ErMnO3 multiferroic composites

Abstract A different kind of multiferroics with composite character has been studied. Detailed study on electrical and dielectric properties of structurally characterized multiferroic composites xLa0.7Sr0.3MnO3–(1 − x)ErMnO3 (where, x = 0, 0.1, 0.15, 0.2, 1), prepared through chemical ‘pyrophoric reaction’ technique, have been presented. Average particle size of the composites is found to be in nanometric region. Both structural and magnetic studies confirm almost complete immiscibility within the mixture of two compounds of La0.7Sr0.3MnO3 and ErMnO3 having nearly identical chemical formula. Impedance value is found to be decreased with increasing La0.7Sr0.3MnO3 content in the composites that can be attributed to the improved electrical connectivity in the sample. Dielectric study reveals that pure ErMnO3, 0.1La0.7Sr0.3MnO3–0.9ErMnO3 and 0.15La0.7Sr0.3MnO3–0.85ErMnO3 composites exhibiting ferroelectric relaxor behavior, whereas 0.2La0.7Sr0.3MnO3–0.8ErMnO3 composite is found to be strongly diffusive ferroelectric sample. Appearance of a distinct hump in dielectric constant of 0.1La0.7Sr0.3MnO3–0.9ErMnO3 composite at the vicinity of para-ferromagnetic transition temperature may be due to some sort of magneto-electric coupling in these composites.