Ferromagnetic-paramagnetic Phase Transition Research Articles

Magnetic transition of ytterbium atoms confined in optical superlattice with local ferromagnetic interaction

We used the density matrix renormalization group to study the ground state of ytterbium atoms (171Yb) for the Hund lattice model, where the delocalized atoms are confined in a onc-dimensional optical superlattice and his number is one third of the lattice sites. We found a paramagnetic-ferromagnetic quantum phase transition for any value of the potential strength. The local critical ferromagnetic coupling decreases as the superlattice potential increases.

Effect of Zn substitution on magnetic properties and magnetic entropy change in La0.7Ba0.25Nd0.05Mn1-xZnxO3 (x = 0.03 and 0.05) synthesized by using sol-gel method

This investigation explored the structural, magnetic, and magnetic entropy change characteristics of La0.7Ba0.25Nd0.05Mn1-xZnxO3 (x = 0.03 and 0.05) synthesized through the sol-gel method. The structural analysis revealed the crystallization of both samples in a Rhombohedral structure with the R-3c space group. The examination of magnetic properties indicated a suppression in magnetic behavior, with the ferromagnetic-paramagnetic transition temperature (TC) decreasing from 285 K to approximately 260 K with an increase in Zn content (x) from 0.03 to 0.05, respectively. The maximum value of magnetic entropy change (−ΔSM) under an applied magnetic field of 50 kOe was determined to be 3.96 J/kg·K for x = 0.03 and 2.27 J/kg·K for x = 0.05. Analysis of Arrot plots and the universal curve of magnetic entropy change confirmed that the ferromagnetic-paramagnetic phase transition observed in both samples exhibits a second-order phase transition (SOPT) transformation.

Study of AC Susceptibility of La0.8Sr0.2MnO3 at Different Frequencies

In the present work, the structural and ac magnetic susceptibility as a function of temperature at different frequencies of perovskite type La08Sr0.2MnO3 (LSMO) compound have been discussed. Conventional solid-state route was used to synthesize LSMO compound. Orthorhombic crystal structure with Pnma space group of the compound was witnessed from the analysis of X-ray diffractograms by Rietveld refinement. The real (χꞌ) and imaginary (χꞌꞌ) part of the ac susceptibility of the compound have been studied. The real part of magnetic susceptibility (χꞌ) of La0.8Sr0.2MnO3 sample increases as temperature decrease. This indicates that the paramagnetic-ferromagnetic phase transition occurs. At different frequencies, i.e. 100Hz and 500Hz the Curie temperature Tc are 326K and 336K respectively. Peaks observed in the imaginary part χꞌꞌ) of magnetic susceptibility plot indicate the presence of sample inhomogeneity.

A DFT and Monte Carlo studies of physical properties of the Fe2N compound

In this paper, we studied the magnetism of Fe2N, using the ab initio and Monte Carlo studies. The magnetic moment and the exchange couplings are deduced by ab initio calculations. The obtained density of states is not symmetrical with respect to the axis of energy proving the ferromagnetic character of this compound. Any gap energy, at the Fermi level, is found confirming the metallic character of this compound. The Hamiltonian of this system consists of several physical parameters. Both the magnetic entropy and the maximum magnetic entropy are obtained. The relative cooling power and the magnetic hysteresis cycle are illustrated. The transition temperature TC value has been deduced and found to be about 252.01 K. This value is in good agreement with the experimental results presented. Also, we found that the magnetizations decrease rapidly to zero with increasing temperature. This is due to the ferromagnetic-paramagnetic phase transition caused by thermal energy.

Structural and critical properties of Pr0.5Sr0.5MnO3 nanoparticle

In this work, a sample of Pr0.5Sr0.5MnO3 nanoparticles with an average crystalline size of <D> = 58 ± 2 nm was prepared by a combination of reactive milling method for 6 h at room temperature and heat treatment at the 1100 °C for 0.5 h. The x-ray diffraction analysis revealed the existence of a Pr0.5Sr0.5MnO3 single phase with the tetragonal structure (I4/mcm space group). Temperature and magnetic field dependences of magnetisation measurements indicated a coexistence of two magnetic phase transitions. One is the antiferromagnetic-ferromagnetic transition at T N = 150 K. The other is the second-order ferromagnetic-paramagnetic phase transition at T C = 273.5 K. Using the modified Arrott plots and the Kouvel-Fisher methods, the critical isotherm analysis, and the scaling relation, the magnetic order in Pr0.5Sr0.5MnO3 nanoparticle sample has been pointed out. Accordingly, the critical exponents were found to be β = 0.486, γ = 1.181, and δ = 3.249. These values are quite close to the allowable exponents of the mean field model, suggesting an existence of the long-range ferromagnetic order. A slight deviation from the mean field model has been explained by the formation of the core/shell structure in Pr0.5Sr0.5MnO3 nanoparticle.

Finite-temperature ferromagnetic transition in coherently coupled Bose gases

A paramagnetic-ferromagnetic quantum phase transition is known to occur at zero temperature in a two-dimensional coherently coupled Bose mixture of dilute ultracold atomic gases provided the interspecies interaction strength is large enough. Here we study the fate of such a transition at finite temperature by performing numerical simulations with the stochastic (projected) Gross-Pitaevskii formalism, which includes both thermal and beyond mean-field effects. By extracting the average magnetization, the magnetic fluctuations and characteristic relaxation frequency (or critical slowing down), we identify a finite-temperature critical line for the transition. We find that the critical point shifts linearly with temperature and, in addition, the three quantities used to probe the transition exhibit a temperature power-law scaling. The scaling of the critical slowing down is found to be consistent with thermal critical exponents and is very well approximated by the square of the spin excitation gap at zero temperature.

Quantum phase transitions in the triangular coupled-top model

We study the coupled-top model with three large spins located on a triangle. Depending on the coupling strength, there exist three phases: disordered paramagnetic phase, ferromagnetic phase, and frustrated antiferromagnetic phase, which can be distinguished by the mean-field approach. The paramagnetic-ferromagnetic phase transition is accompanied by the breaking of the global ${Z}_{2}$ symmetry, whereas the paramagnetic-antiferromagnetic phase transition is accompanied by the breaking of both the global ${Z}_{2}$ symmetry and the translational symmetry. Exact analytical results of higher-order quantum effects beyond the mean-field contribution, such as the excitation energy, quantum fluctuation, and von Neumann entropy, can be achieved by the Holstein-Primakoff transformation and symplectic transformation in the thermodynamic limit. Near the quantum critical point, the energy gap closes, along with the divergence of the quantum fluctuation in certain quadrature and von Neumann entropy. Particular attention should be paid to the antiferromagnetic phase, where geometric frustration takes effect. The critical behaviors in the antiferromagnetic phase are quite different from those in the paramagnetic and ferromagnetic phases, which highlight the importance of geometric frustration. The triangular coupled-top model provides a simple and feasible platform to study the quantum phase transition and the novel critical behaviors induced by geometric frustration.

Effect of Ca doping on the arbitrary canting of magnetic exchange interactions in La1-xCaxMnO3 nanoparticles

La1-xCaxMnO3 nanoparticles (x = 0.1, 0.2, 0.3) (LCMO NPs) were synthesized using the coprecipitation method. The prepared samples were investigated using x-ray diffraction (XRD), which confirmed the single-phase structure. The nanoparticle’s crystallite size was determined using Debye–Scherrer’s formula. Scanning electron microscopy showed that the size of the nanoparticles was between 33 nm and 55 nm. Energy-dispersive x-ray spectroscopy (EDX) was used to determine the elemental composition of samples. The four-probe method was used to measure the temperature-dependent electrical resistivity. Magnetic properties, such as hysteresis loop, magnetoresistance, and magnetization versus temperature, were measured using a vibrating sample magnetometer. The study of magnetization versus applied magnetic field M(H) showed that, at 77 K, all the loops exhibit ferromagnetism. DC magnetization versus temperature at a 70-Oe-applied field for all samples showed a paramagnetic-ferromagnetic phase transition. A decrease in Curie temperature Tc after increasing the concentration of x was observed. The real and imaginary parts of temperature-dependent ac magnetic susceptibility were measured and revealed a transition from the ferromagnetic to the paramagnetic phase at a particular temperature Tc, with DC magnetization behavior.

Enhanced magnetic refrigerant capacity power in Dy3Ni2 melt-spun ribbons by controlling the solidification rate

Both mechanical and magnetic properties of Dy3Ni2 ingots and melt-spun ribbons were investigated in the present work. The melt spinning rate has an important effect on their performance. The higher the melt spinning rate, the better the ductility, the larger the coercive force of ribbons. With increasing the spinning rate, the intensity of the diffraction peak suggesting the presence of polycrystalline becomes weaker and weaker, and eventually disappeared. The magnetic phase transition temperature is decreased from 66 K to 38 K with increasing the spinning rate. All samples undergo a second order paramagnetic-ferromagnetic phase transition. The full-width-at-half maximum of the temperature dependence of magnetic entropy change curve in Dy3Ni2 ribbons was much larger than that of Dy3Ni2 ingot. So a high refrigerant capacity power about 530 J.kg−1 of Dy3Ni2 ribbons was achieved.

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.

Toward Sabatier Optimal for Ammonia Synthesis with Paramagnetic Phase of Ferromagnetic Transition Metal Catalysts.

The Sabatier principle defines the essential criteria for being an ideal catalyst in heterogeneous catalysis, while approaching the Sabatier optimal is a major pursuit in catalyst design. The Haber-Bosch (H-B) process, converting nitrogen (N2) and hydrogen (H2) to ammonia (NH3), is a holy grail reaction for humans and also a great model reaction for fundamental research, where the established volcano plot between ammonia synthesis activity and nitrogen binding energy among metals has successfully guided new catalyst design. However, reaching the top of the activity volcano is still very challenging. Herein, we identify an elegant strategy to promote the ferromagnetic (FM) catalysts to be the Sabatier optimal of ammonia synthesis via a second-order ferromagnetic-paramagnetic phase transition, which represents an ideal and novel interdisciplinary of the aforementioned century-old classic principle, reaction, and theory in chemistry, physics, and material science. The paramagnetic (PM) Co and Ni metals could have 2-4 orders of magnitude higher ammonia synthesis activity than their ferromagnetic counterparts, holding the potential to achieve a near-ambient H-B process. We believe that our discovery will open a novel avenue for revisiting the catalytic performances of paramagnetic phases of ferromagnetic materials in heterogeneous catalysis.

Magnetocaloric and Giant Magnetoresistance Effects in La-Ba-Mn-Ti-O Epitaxial Thin Films: Influence of Phase Transition and Magnetic Anisotropy.

Magnetic perovskite films have promising properties for use in energy-efficient spintronic devices and magnetic refrigeration. Here, an epitaxial ferromagnetic La0.67Ba0.33Mn0.95Ti0.05O3 (LBMTO-5) thin film was grown on SrTiO3(001) single crystal substrate by pulsed laser deposition. High-resolution X-ray diffraction proved the high crystallinity of the film with tetragonal symmetry. The magnetic, magnetocaloric and magnetoresistance properties at different directions of the applied magnetic field with respect to the ab plane of the film were investigated. An in-plane uni-axial magnetic anisotropy was evidenced. The LBMTO-5 epilayer exhibits a second-order ferromagnetic-paramagnetic phase transition around 234 K together with a metal-semiconductor transition close to this Curie temperature (TC). The magnetic entropy variation under 5 T induction of a magnetic field applied parallel to the film surface reaches a maximum of 17.27 mJ/cm3 K. The relative cooling power is 1400 mJ/cm3 K (53% of the reference value reported for bulk Gd) for the same applied magnetic field. Giant magnetoresistance of about 82% under 5 T is obtained at a temperature close to TC. Defined as the difference between specific resistivity obtained under 5 T with the current flowing along the magnetic easy axis and the magnetic field oriented transversally to the current, parallel and perpendicular to the sample plane, respectively, the in-plane magneto-resistance anisotropy in 5 T is about 9% near the TC.

Griffiths-like phase, large magnetocaloric effect, and unconventional critical behavior in the NdSrCoFeO6 disordered double perovskite

A B-site disordered double perovskite $\mathrm{NdSrCoFe}{\mathrm{O}}_{6}$ was successfully synthesized by the conventional sol-gel method. Detailed experimental analyses revealed that $\mathrm{NdSrCoFe}{\mathrm{O}}_{6}$ crystallizes in the orthorhombic $Pnma$ space group, in which ${\mathrm{Co}}^{2+/3+}$ and ${\mathrm{Fe}}^{3+/4+}$ ions are randomly distributed at the BB\ensuremath{'} sites, and ${\mathrm{Sr}}^{2+}$ and ${\mathrm{Nd}}^{3+}$ ions are respectively ordered at the A and A\ensuremath{'} sites in an alternating arrangement along the $c$ direction. $\mathrm{NdSrCoFe}{\mathrm{O}}_{6}$ has a semimetallic-to-semiconducting transition nature, and a paramagnetic-ferromagnetic (FM) second-order phase transition originating from the complex hybridization between Co $3d$ and O $2p$ states is also found to occur at ${T}_{\mathrm{C}}\ensuremath{\approx}150$ K. Then the spin coupling between ${\mathrm{Fe}}^{4+}\ensuremath{\leftrightarrow}{\mathrm{Co}}^{3+}$ and ${\mathrm{Fe}}^{3+}\ensuremath{\leftrightarrow}{\mathrm{Co}}^{2+}$ randomly distributed on the B and B\ensuremath{'} sites leads to a FM cluster spin-glass behavior with characteristic parameters of $k=0.01, {T}_{\mathrm{SG}}=82.7$ K, $zv=1.89$, and ${\ensuremath{\tau}}_{0}=0.46\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ s. Additionally, Griffiths-like phase behavior was observed in the region ${T}_{\mathrm{C}}&lt;T&lt;{T}_{\mathrm{GP}}$, with ${T}_{\mathrm{GP}}=245$ K, consistent with the power law exponent of $\ensuremath{\lambda}=0.74$. The maximum isothermal magnetic entropy change $\ensuremath{-}\mathrm{\ensuremath{\Delta}}{S}_{M}^{\mathrm{max}}\ensuremath{\approx}1.84\phantom{\rule{0.16em}{0ex}}\mathrm{J}\phantom{\rule{0.16em}{0ex}}\mathrm{k}{\mathrm{g}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$ and relative cooling power $\ensuremath{\approx}43.8\phantom{\rule{0.16em}{0ex}}\mathrm{J}\phantom{\rule{0.16em}{0ex}}\mathrm{k}{\mathrm{g}}^{\ensuremath{-}1}$ under a field of 40 kOe also indicate a magnetocaloric coupling wherein fitted critical exponents $\ensuremath{\beta}=1.384, \ensuremath{\gamma}=0.621$, and $\ensuremath{\delta}=1.421$ are far from any conventional universality class. Density functional theory calculations demonstrated spin short- and long-range ordering competitions for Fe/Co at BB\ensuremath{'} sites, which arise predominantly from the stronger negatively charged ligand interaction with Co $3d$ orbitals and the weakest Fe $3d$ orbitals. This unconventional behavior is expected to be the main reason for the experimentally observed magnetic exchange distance decreasing with $J(r)\ensuremath{\approx}{r}^{\ensuremath{-}4.7}$.

Magnetic properties and critical behavior of the perovskite manganite La0.825Sr0.175MnO3

Polycrystalline La0.825Sr0.175MnO3 was prepared by solid state reaction method. It exhibits a ferromagnetic–paramagnetic phase transition at TC∼286 K. The intrinsic magnetic properties were clarified by the scaling theory and the isothermal magnetization measured around TC. Based on the modified Arrott plot, Kouvel–Fisher method and Widom relation, the critical exponents are determined to be β=0.308(7), γ=1.065(8), δ=4.457(17). Normalization of the critical exponents shows that the extended exchange interaction decays with J∼r−4.861, consistent with Tricritical mean field model. Rhodes–Wohlfarth ratio PC/MS>1 suggests that La0.825Sr0.175MnO3 is completely itinerant ferromagnet.

Magnetic and Magnetocaloric Properties of SrRu&lt;sub&gt;1−x&lt;/sub&gt;Fe&lt;sub&gt;x&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;

We have systematically investigated the crystalline and electronic structures, magnetic and magnetocaloric properties of polycrystalline SrRu1−xFexO3 (x = 0 and 0.1) samples fabricated by the solid-state reaction method. The X-ray diffraction analyses of the samples indicated single phase orthorhombic perovskite structure. A thorough analysis of X-ray-absorption-based electronic structure revealed that both Fe2+ and Fe3+ ions are present in x = 0.1, in which concentration of Fe3+ ions is higher than that of Fe2+ ions. More careful analyses on the isothermal magnetization data derived from the Banerjee’s criterion demonstrated that the ferromagnetic-paramagnetic phase transition in all samples belongs to the second-order phase transition type. These results were also confirmed by a recently proposed quantitative criterion, which considered an exponent n from the magnetic field and temperature dependences of the magnetic entropy change (ΔSm). Especially, around TC, we have found that the ΔSm reaches the maximum values of 1.65 and 1.32 J.kg−1.K−1 for x = 0 and 0.1, respectively, for a field change of ΔH = 50 kOe. Magnetic-field dependences of the maximum magnetic-entropy change (ΔSmax) obey a power law of ΔSmax(H) ∝ Hn, where the values of n = 0.92–0.94 are far from the mean-field-theory value (2/3), indicating short-range magnetic order existing in the samples.

Increased exchange interaction range by Fe substitution in Ni3-xFexAl: Evidence from critical behavior

The critical behavior of Fe substituted intermetallic compounds Ni3-xFexAl (x = 0, 0.18, and 0.36) has been investigated around the paramagnetic-ferromagnetic (PM-FM) phase transition based on the static magnetization data. Reliable critical exponents (β, γ, and δ) and transition temperature TC are determined for the compounds, by using Modified Arrott plot, Kouvel-Fisher plot, and critical isotherm plot. The self-consistence and reliability of the obtained critical exponents are further verified by the Widom scaling relation δ = 1 + γ/β and scaling equations of the state M(H,ε) = εβf±(H/εβ+γ). It is found that, Fe substitution for Ni dramatically increases TC from 44.44 K for x = 0 to 301.20 K for x = 0.36. The critical exponents for the three compounds are all found to follow mean-field model. The exchange interaction J(r) is found to decay asr-4.657,r-4.434, and r-4.257 for x=0, 0.18 and 0.36, respectively. The results suggest that, a long range mean-field spin interaction dominates in Ni3-xFexAl (0≤x≤0.36) series. Furthermore, Fe substitution to Ni site is found to increase the spin interaction distance to longer range.

Evidence for additional third-order transitions in the two-dimensional Ising model.

We employ the microcanonical inflection-point analysis method, developed for the systematic identification and classification of phase transitions in systems of any size, to study the two-dimensional Ising model at various lattice sizes and in the thermodynamic limit. Exact results for the density of states, which were obtained by exact algorithmic computation, provide evidence for higher-order transitions in addition to the well-studied second-order ferromagnetic-paramagnetic phase transition. An independent third-order phase transition is identified in the ferromagnetic phase, whereas another third-order transition resides in the paramagnetic phase. The latter is a dependent transition, i.e., it is inevitably associated with the critical transition, but it remains separate from the critical point in the thermodynamic limit. For a deeper insight into the nature of these additional transitions, a detailed analysis of spin clusters is performed.

Magnetic and electrical transport studies of polycrystalline Sr1− x Bi x Fe12O19 (x = 0, 0.01, and 0.02)

Bismuth-substituted strontium hexaferrites, Sr1−x Bi x Fe12O19 for x = 0, 0.01 and 0.02, are studied via powder neutron diffraction (ND), magnetization (M) studies, Mössbauer spectroscopy, and electrical transport. ND results show an indication of increasing Fe2+ at 12k crystallographic sites (which is supported by Mössbauer results), with increasing Bi in the sample. They also suggest an increase in strain due to Bi substitution for the polyhedral associated with 2a and 2b spin-up and 4f1 spin-down sites. The M measurements over a wide temperature range (3–823 K), shows irreversibility in zero field cooled (ZFC) and field cooled data right below the Curie temperature, along with the Hopkinson peak in the ZFC data. The temperature dependence of saturated magnetization follows the Bloch relation but that of the coercive field shows unconventional behavior. The coercive field data is fitted using an equation devised by taking into consideration of all the three anisotropies. The critical exponents at the ferromagnetic–paramagnetic phase transition boundary, calculated using modified Arrott plots, are slightly overvalued as per mean-field theory. The temperature dependence of resistivity displays nearest-neighbor hopping conduction in all the three samples. The conductivity increases with increasing Bi in the sample, due to the increasing Fe2+ content, which facilitates the electron hopping between Fe sites. The magnetoresistance measured at various sub-room temperatures for all the compounds shows the interplay of anisotropy magnetoresistance (AMR) and giant magnetoresistance (GMR). Low temperature data are dominated by GMR and gradual participation of AMR increases as room temperature is approached.

Correlating Crystallography, Magnetism, and Electronic Structure Across Anhysteretic First-Order Phase Transition in Pr2In

Temperature-dependent powder X-ray diffraction and magnetization measurements of Pr2In conclusively prove that the unusual anhysteretic first-order paramagnetic-ferromagnetic phase transition in the compound is related to concurrent changes in both the magnetic and crystallographic lattices. At the same time, the hexagonal Ni2In-type structure is stable at least between 6 and 298 K, including at T C = ∼57 K. From the density functional theory calculations, the electronic structure of the compound is extraordinarily sensitive to minor changes in lattice parameters that occur across the phase transition, revealing the origin of strong magnetoelastic coupling. In the vicinity of T C, the maximum entropy change, ΔS Max = −16 J Kg−1 K−1 induced by a moderate magnetic field change of 20 kOe (ΔS Max = −20 J Kg−1 K−1 for 50 kOe magnetic field change) is comparable to other known potentially functional materials demonstrating large cryogenic magnetocaloric effect.

Magnetic, magnetocaloric and thermoelectric properties of the intermetallic LaMn2Si2 compound: a theoretical study

ABSTRACT The deficiency of materials with coexisting transport and magnetocaloric effect has prevented the development of intermetallic-based magnetic refrigeration applications. Therefore, intermetallic alloys are non-toxic, inexpensive, and low density. The presents work investigates the magnetic, magnetocaloric, and thermoelectric properties of the intermetallic LaMn2Si2 compound by using the first-principles calculations and Monte Carlo simulations. From the Ab initio calculation, the exchange coupling and anisotropy interactions are calculated. Also, the magnetic and magnetocaloric properties are determined using Monte Carlo simulations. It is found that the intermetallic LaMn2Si2 compound exhibits a second-order ferromagnetic-paramagnetic phase transition around TC , this value of temperature is in good agreement with the experimental value. Finally, the thermoelectric properties are discussed. Our results improve that this material is applicable for magnetic refrigeration at Curie temperature.