Banerjee Criterion Research Articles

Influences on the structure, magnetic, and magnetocaloric effect of La0.8Sr0.2MnO3 ceramics by Co ion doping with sol-gel method and first-principles calculations

This paper investigated the impact of Co ions doping on the structure, magnetic properties, and magnetocaloric effect for La0.8Sr0.2Mn1-xCoxO3 ceramics (LSMCO) by sol-gel method and first-principles calculations The use of first-principles calculations was provided for subsequent experiments. The sol-gel preparation of LSMCO ceramics and sintered at 950 °C for 10 h. It was shown that the samples' cell volume and lattice constants changed slightly with increasing Co2+ doping but remained a rhombohedral structure (No.167, R-3c space group) by statistics of TEM and XRD. The average particle size for the LSMCO ceramics ranged from 130 nm to 170 nm. LSMCO's chemical composition was verified by EDS and XPS and it was demonstrated that Co2+ was successfully doped. The oxidation state of La was found to be +3, Mn is a mixture of Mn3+ and Mn4+ valence states, and Co is a mixture of Co3+ and Co2+ valence states using XPS. In the vicinity of Tc, all samples presented the second-order magnetic phase transition from ferromagnetic to paramagnetic resorting to normalization and the Banerjee criterion. The Tc dropped from 292 K to 237 K with increasing Co2+ doping. The blocking temperature and the saturation magnetization were suppressed by the Co2+ substitution while the maximum magnetic entropy change of the LSMCO ceramics was observed to reduce as Co2+ increased. When the external magnetic field is 5 T, the La0.8Sr0.2Mn0.95Co0.05O3 ceramics has a Tc of 292 K and a maximum magnetic entropy change value of 3.47 J/(kg K).

Changes in microstructure, magnetocaloric effect and critical behavior of La0.8Sr0.2MnO3 manganites by K/Co doping

We prepared La0.8-xKxSr0.2Mn0.95Co0.05O3 (0 ⩽ x ⩽ 0.1) (LKSMCO) through the modified sol-gel method (S-G) and its structure. Then, the magnetic, magnetocaloric, and critical behavior were analyzed. LKSMCO was confirmed to be the rhombohedral structure within the R-3c space group (No.167) using transmission electron microscopy and X-ray diffraction. For validating the chemical composition of LKSMCO, X-ray photoelectron spectroscopy and EDS were applied, showing that K+ was successfully doped. Phase transition of LKSMCO from paramagnetic to ferromagnetic phase near Curie temperature (Tc) was confirmed with a Magnetic Property Measurement System (MPMS). Using normalization and Banerjee's criterion, LKSMCO was demonstrated to be the second-order magnetic phase transition (SOMPT). As shown from the applied magnetic field, the maximal magnetic entropy (−ΔSMmax) of LKSMCO near Tc was 3.87 J/(kg K) (x= 0.00), 4.28 J/(kg K) (x= 0.05) and 4.44 J/(kg K) (x= 0.10). We employed the Kouvel-Fisher approach (KF) and modified Arrott plots to confirm the values of γ, δ, and β. This indicates that critical exponents of LKSMCO were consistent with the Mean-filed model.

Weak magnetic doping effect on the magnetic transition, magnetocaloric properties, and super-invar behavior in TbCo2Vx system

In this work, the V-doped effect on the magnetic transition and magnetocaloric properties have been studied systematically for TbCo2Vx (0 ≤ x ≤ 0.2) series. All samples were characterized by powder X-ray diffraction (XRD) as cubic structures (Fd-3 m) at room temperature. The Curie temperatures TC of TbCo2Vx decrease monotonically from 234 K (x = 0) to 214 K (x = 0.2) corresponding to a monotonically increasing value of lattice a. The slightly diminished magnetic saturation moment MS from 6.35 μB/f.u to 6.12 μB/f.u with the x value increasing indicates weak magnetic doping in this system, which can also be reflected in the slight decrease of the maximum values of magnetic entropy change (-ΔSM) from 6.23 J kg-1K−1 to 5.27 J kg-1K−1 (0–5 T). X-ray photoelectron spectrum (XPS) measurements confirm that the weak magnetic doping originates from the multivalences of V2+ and V4+, compared with other normally nonmagnetic V-doped cases reported before. Both the Banerjee criteria and rescaled magnetic entropy change lines deny the first-order transition in parent compound TbCo2 as reported recently. Almost zero thermal expansion near TC in TbCo2 with thermal expansion coefficient αl = -1.43 × 10-6 K−1 indicates weak magnetostriction, which is another experimental hint for second-order transition. The deviation of the critical exponents to Mean-field theory in TbCo2 implies some crystal defects and inhomogeneous polycrystalline distribution inside, which should also be a key point for the divergence of first-order and second-order transition in different samples of TbCo2 as reported before. Super-invar behavior with αl = 4.4 × 10-7 K−1 was found in the x = 0.2 component by macro-thermal expansion measurement.

Effect of Cr substitution on structural, magnetic, magnetocaloric and critical behaviors of La0.7Y0.05Ba0.25MnO3 perovskite manganite

A thorough investigation was conducted into the structural, magnetic, and critical properties of La0.7Y0.05Ba0.25Mn1-xCrxO3 (x = 0 and 0.15) perovskite manganite synthesized using the sol-gel method. The samples possess an orthorhombic structure with the Pnma space group according to X-ray diffraction (XRD) patterns. The average ion radii of the B-site cation (<rB>), the unit cell volume (V), and <θMn,Cr–O–Mn,Cr > bond angle decreased with Cr substitution. While the average bond distance, <dMn,Cr–O>, and Goldschmidt tolerance factor (tG) increased. The samples present a magnetic transition from a paramagnetic (PM) phase to a ferromagnetic (FM) phase at Curie temperature (TC). Addition of Cr to La0.7Y0.05Ba0.25MnO3 decreased the TC value from 310 K (for x = 0 sample) to 258 K (for x = 0.15 sample). Using Banerjee's criteria, second-order phase transitions were determined for the samples. Both samples showed significant maximum entropy change |ΔSMmax| and relative cooling power (RCP) whose values decreased from (6.40 J Kg−1 K−1 and 231 J Kg−1 for x = 0) to (4.45 J Kg−1 K−1 and 185 J Kg−1 for x = 0.15), respectively. These values indicate that the La0.7Y0.05Ba0.25Mn1-xCrxO3 manganites exhibit favourable magnetocaloric effect (MCE) and demonstrate promising potential for application as materials in magnetic refrigeration technology. The estimated critical exponents (β, γ, and δ) for the x = 0 sample align with the 3D-Ising model, while for x = 0.15, they closely resemble the 3D-Heisenberg model. This shift in the universality class can be attributed to the interplay between competing ferromagnetic double-exchange and antiferromagnetic super-exchange interactions that exist within the prepared samples.

Itinerant ferromagnetism and room temperature giant magnetocaloric effect in (Mn0.6Fe0.4) (Ni0.5Co0.5) Si shape memory alloy

In this article, the feasibility of obtaining a magneto-structural coupling over a wide working temperature range of about 127 K (from 206.5 K to 333.5 K) with negligible thermal hysteresis in combination with the structural, microstructural, magnetic, and magnetocaloric properties of a 50 % Co-doped (at the Ni site) polycrystalline (Mn0.6Fe0.4) (Ni0.5Co0.5) Si (MFNCS-0.5) magnetic shape memory alloy (MSMA) has been thoroughly investigated. Along with leaf-like microstructure, at room temperature, the system shows a mixed phase of TiNiSi type low-temperature high-magnetic (ferromagnetic) orthorhombic martensite and Ni2In type high-temperature low-magnetic (paramagnetic) hexagonal austenite, with the dominance of the second one. To estimate the magnetocaloric effect (MCE) across the phase transition, the isothermal magnetic measurement technique has been employed. The merging of heating and cooling iso-field thermo-magnetization (M-T) curves, the presence of negligible thermal hysteresis in the MH curves, universal magnetic entropy curves, a proposed phenomenological model (across the Curie temperature), and the positive slopes of the Arrott plot (Banerjee criterion) show that the first-order structural and magnetic transition are coupled along with a second-order ferromagnetic to paramagnetic (FM → PM) phase transition (SOPT). By extrapolating the Arrott plot to the H/M = 0 axis the spontaneous magnetization value very close to 0 K, Ms(0), is found to be 71.92 emu/g (∼1.83 µB/f.u.). The linear dependency of MS2T on T2 below SOPT and the RWR (Rhodes–Wolhfarth ratio) = 4.29 > 1 indicate the long-range itinerant ferromagnetism in this alloy. A giant magnetic entropy change (ΔSm) of 25.77 J kg−1 K−1 and a refrigerant capacity (RC) of 472.83 J kg−1 are obtained at 6 T field. This observed magnetic refrigerant's key characteristics, including a giant magnetocaloric effect (MCE) near room temperature (RT), negligible thermal hysteresis loss, a wide operating temperature range of 127 K, and the use of cost-effective, non-toxic constituent elements, make it a suitable and very promising member for applications in solid-state refrigeration technology near RT.

Effects of A, B-site multiple ion co-doping on the structure, magnetic, magnetocaloric effect, and critical behavior of La0.7-xNd0.1Sr0.2KxMn0.95Ni0.05O3 ceramics

The effects of K+ doping on structure, magnetic characteristics, magnetocaloric properties, and critical behavior of La0.7-xNd0.1Sr0.2KxMn0.95Ni0.05O3 (LNSKMNO) ceramics (x = 0.00, 0.05, and 0.10) were investigated. The X-ray diffraction and refinement findings revealed that LNSKMNO exhibited a distinctive rhombohedral structure of the R-3c space group (No. 167). To validate the chemical composition of LNSKMNO ceramics, EDS spectroscopy and X-ray photoelectron spectroscopy (XPS) were utilized. The magnetization of LNSKMNO exhibited a temperature-dependent behavior, revealing a phase transition from the ferromagnetic (FM) phase to the paramagnetic (PM) phase at approximately the Curie temperature (Tc). By utilizing normalization and Banerjee's criterion, the magnetic phase transition of LNSKMNO was determined to be a second order magnetic phase transition. The maximal magnetic entropy (−ΔSMmax) of LNSKMNO around Tc was 4.24, 4.53, and 4.07 J/(kg K) at the 5 T external magnetic field (H). The Kouvel-Fisher approach and modified Arrott plot were used for determining the values of the critical exponents of β, γ, and δ. The critical exponents for LNSKMNO ceramics generally conformed to those obtained based on the Mean-field model.

Structural, Morphological, and Magnetocaloric Properties of Nanocrystalline Pr0.7La0.3MnO3

Abstract The structural, morphological, magnetic, and magnetocaloric properties of nanocrystalline Pr0.7La0.3MnO3 (PLMO), synthesized by using a wet chemical Sol-gel method, have been investigated. The single-phase nature of nanocrystalline PLMO with orthorhombic crystal structure along with the Pbnm space group was confirmed by Rietveld analysis of the X-ray diffraction pattern. The average crystallite size and lattice microstrain were determined using the Williamson-Hall technique, and they were found to be ~ 28 nm and ~ 0.00137, respectively. Transmission electron microscopy shows the particle size and structural characteristics of the sample. Temperature-dependent magnetization data show paramagnetic to ferromagnetic transition. According to Banerjee criterion, the positive slope of Arrott's plot for nanocrystalline PLMO indicates the second-order magnetic phase transition. In a 5 T external magnetic field, the maximum magnetic entropy change (∆SM) was found to be 2.47 J/kg K. The refrigerant capacity and relative cooling power were calculated and the values are 193.3 and 277.57 J/kg, respectively, under a 5 T applied external magnetic field.

Effects of Ca substitution on magnetic and magnetocaloric properties in PrBa1-xCaxMn2O6 system

In this study, we have examined the effect of Ba substitution by Ca on the magnetic, and magnetocaloric properties of PrBa1-xCaxMn2O6 (x = 0, 0.2 and 0.3) double perovskite manganites produced using sol-gel method. The samples were indexed in orthorhombic structure (with space group of Pbnm). The temperature-dependent magnetization, M(T), measurements indicate that all samples have a magnetic phase transition from ferromagnetic (FM) to paramagnetic (PM) state with increasing temperature. Curie temperature (TC) decreases with increasing Ca content in the main lattice. From the magnetic field dependence of magnetization measurements, M(H), maximum magnetic entropy change (−ΔSMmax) values were calculated as 4.07, 4.12, and 5.04 Jkg−1K−1 under 5 T for PrBaCaMn2O6, PrBa0.8Ca0·2Mn2O6, and PrBa0.7Ca0·3Mn2O6 samples, respectively. Relative cooling power (RCP) values below 5 T were determined as 214.16, 227.14 and 279.62 Jkg-1 based on the increasing Ca content. The −ΔSMmax and RCP values enhance with increasing Ca content, respectively. The nature of the phase transition, checked by Banerjee criterion and Franco's universal master curves, was found to be second order magnetic phase transition (SOMT).

Critical behavior of the cubic ErNi2 Laves compound nearby the Ferro-paramagnetic phase transition

In this article, we analyze the critical behavior of the cubic Laves crystalline binary intermetallic compound ErNi2 near its second-order ferromagnetic (FM) to paramagnetic (PM) transition (6.9 K). Both the normalized thermal dependencies of the magnetic entropy change curves and the Banerjee criterion confirm the second order nature of the transition. By comparing the normalized slopes, we found that the Tricritical mean-field model is the best model to calculate the critical exponent value of ErNi2. Based on the modified Arrott plots, the final critical exponents are determined to be β = 0.164(2) and γ = 0.821(9), which are the closest to the Tricritical mean-field model, except for a litter differences. Moreover, the accuracy and reliability of these exponents were confirmed by both the Widom scaling relation and the scaling hypothesis. Our results provide new insight into understanding this compound's magnetic interactions.

Magnetocaloric effect and critical behavior of the Mn5Ge3−xZnx alloys

In this paper, the magnetocaloric properties, phase transition and critical behavior of Mn5Ge3−xZnx (x = 0.1, 0.2 and 0.3) compounds fabricated by the arc-melting method were investigated. The Curie temperature and the magnetic entropy change of Mn5Ge3−xZnx alloys decrease with doping of Zn. The normalized curves of universal behavior further demonstrate the feature of second-order transition in the Mn5Ge3−xZnx alloys, consistent with the results of the Landau coefficient and Banerjee criterion analysis. To explore the properties near the phase transition, we investigated the critical behavior of this series using modified Arrott plots, Kouvel-Fisher method and critical isotherm curves. The critical exponents β, γ and δ were calculated in accordance with the Widom scaling relation, and magnetic state equation, demonstrating the experimentally obtained exponents are accurate. The spontaneous magnetization derived from the isothermal entropy change calculated from Maxwell equation, is in agreement with the spontaneous magnetization calculated from the curves, proving the validity of calculating the spontaneous magnetization from the curves.

Microstructure, magnetism and critical behavior of hot pressed Ni-Mn-Ga/Al magnetocaloric composites with enhanced thermal conductivity and mechanical properties

In the application of magnetic refrigeration technology, magnetocaloric materials are required to possess large magnetocaloric effect and broad working temperature range with good thermal conductivity and mechanical properties. To address this elusive combination of properties, we prepared Ni-Mn-Ga/Al magnetocaloric composites via hot pressing method. Phase composition and element distribution revealed the influence of sintering temperature on composites' microstructure. The magnetic properties and magnetocaloric effect of hot pressed Ni-Mn-Ga alloy and Ni-Mn-Ga/Al composites were studied, indicating their largely broadened working temperature range of 71 K and maximum magnetic entropy change of 2.2–3.0 J/(kg K). Based on thermomagnetic measurements, critical behavior was investigated via modified Arrott plots and Kouvel-Fisher method, and mean-field theory model could best explain the samples' critical behavior. The Ni-Mn-Ga/Al composite also possessed enhanced fracture stress of 306 MPa, much higher than that of bulk Ni-Mn-Ga alloy by arc melting. The good magnetocaloric response of the composites, which is comparable or even better than that of many other Ni-Mn-Ga particle and microwire counterparts, is accompanied by improved thermal conductivity and mechanical properties, extending the applicability of magnetocaloric materials with large specific surface area. The novel findings of this systematic study offer new insights into magnetocaloric composites and provide an approach to reach a significant balance when fulfilling multiple requirements of magnetic refrigeration technology. • Hot pressed Ni-Mn-Ga/Al was thoroughly studied in view of refrigeration application. • HP samples had good MCE comparable to their counterparts with reduced length scale. • MAP and KF method were used to compute critical exponents and study critical behavior. • Order of phase transition was ascertained by both Banerjee criterion and exponent n. • Thermal conductivity and mechanical properties were improved after making composites.

Unified understanding of the first-order nature of the transition inTbCo2

The determination of the nature of phase transitions, especially those that involve two symmetry-breaking order parameters, is a fundamental issue in condensed matter physics. For the Laves-phase rare-earth--transition-metal intermetallic compounds, their phase transitions involve both magnetic ordering and structural ordering. As a typical material of the Laves-phase intermetallics, ${\mathrm{TbCo}}_{2}$ has been studied extensively for its transition around 230 K. However, the understanding on the nature of this transition has remained controversial (first/second order) for decades. Here, in this paper, based on the criteria that determine first-order and second-order transitions for magnetic materials, which are (1) latent heat, (2) thermal hysteresis, (3) coexistence of phases, and (4) the Banerjee criterion, we show direct evidence to reveal the first-order nature of the transition in ${\mathrm{TbCo}}_{2}$, which is further interpreted by a Landau theory based phenomenological approach. Our work reconciles the lasting arguments on the transition of ${\mathrm{TbCo}}_{2}$ and may pave the way for deepening the understanding on the transitions of magnetic materials that involve both magnetic and structural transitions.

Magnetic performance of amorphous manganese nanoparticles doped with rare earth elements

We studied magnetic and magnetocaloric response in nanoparticle manganite oxides (ABO3-type manganese oxides), which were chemically prepared by sol–gel method with different composition RMnO3 (R = Gd, Tb, Ce) (GMO, TMO, CMO). The structural characterization was performed by EDX (Energy-dispersive X-ray spectroscopy) technique, using TEM (Transmission electron microscopy) methods and XRD and confirmed the nanosized character and morphology of studied manganites. Despite the amorphous character of the samples RMnO3 (R = Gd, Tb), the relatively large magnetic entropy change − ΔSM(7 K) ∼15 J/kgK and − ΔSM (13 K) ∼8 J/kgK has been observed in the case of GMO and TMO, respectively. Sample CMO, despite of its crystalline character, exhibits the lowest magnetic entropy change and the magnetic properties are affected by Jahn-Teller distortion in Mn3O4 nanoparticles (NPs). All systems GMO, TMO, CMO exhibit the Arrott plots with linear behavior and positive slopes that is according to the Banerjee criterion a signature of the second order phase transition. This is in line with our conclusions on the presence of AFM-PM phase transitions in the systems that we drew from ZFC-FC data. Our results confirm that also amorphous manganites especially with Gd show feasible properties for potential magnetic refrigeration applications.

Magnetic, Magnetocaloric, and Electric Transport Properties of Sr2FeMoO6–δ Double Perovskites with Different Degrees of Superstructural Ordering

Pressed strontium ferromolybdate (Sr2FeMoO6−δ) pellets with different oxygen indices δ and degrees of superstructural ordering (SO) are synthesized by solid‐phase and citrate‐gel methods to study magnetic and electric transport behaviors of this compound. The crystalline structure of the samples is found to demonstrate ordering of the Fe and Mo cations, which increases with increase in δ. The saturation magnetization and the Curie temperature of the samples correlate with the degree of SO. The Banerjee criterion indicates that the compounds studied undergo a second‐order phase transition. The temperature dependence of the isothermal change of entropy in magnetic field is determined by the Maxwell approach. The additional low‐temperature annealing is found to change the sample conductivity of metallic type for semiconducting one and significantly increases the magnetoresistance due to intergrain electron tunneling.

Effects of copper substitution to Mn-site on magnetic and magnetocaloric properties of La0.7Sr0.3Mn1-xCuxO3 manganites

In present study, the effects of copper substitution on the magnetic and magnetocaloric properties of La0.7Sr0.3Mn1-xCuxO3 manganite samples were investigated. La0.7Sr0.3Mn1-xCuxO3 samples were obtained by using sol-gel method. X-ray diffraction analyses were performed to determine structural properties such as lattice parameters and crystal structure. The crystal structure of the samples is rhombohedral with space group R3 ̅c. The Cu substitution to the Mn-site causes a decrease in the magnetic phase transition temperature (TC) of the samples. By using Banerjee criterion and Landau theory, the type of magnetic phase transition is determined as second order. From isothermal magnetization measurements, magnetic entropy change (-∆S_M) values were calculated for different magnetic field changes of the samples. The maximum magnetic entropy change value (-∆S_M^max) determined from the temperature dependence of -∆S_M curves for the samples is 3.39 and 2.78 JKg-1K-1 under 5 T, respectively. Relative cooling power (RCP) values of the samples were found as 249.52 and 111.98 Jkg-1 for 5 T, respectively.

Comparative study on the effect of synthesis route on the structural, magnetic, and magnetocaloric properties of La0 .5Ca0.5Mn0.95V0.05O3 manganite

ABSTRACT The influence of the synthesis method on structural, magnetic and magnetocaloric properties of the La0.5Ca0.5Mn0.95V0.05O3 compound has been investigated. The compound was prepared by glycine nitrate process (GNP) and compared to counterparts obtained with solid-state route (S-S) and ball milling (B-M). The structural analysis shows a pure and single-orthorhombic crystalline phase for the GNP compound. A secondary phase LaVO4 was detected for S-S and B-M samples. From magnetization versus temperature analysis, different magnetic behaviors were distinguished when moving from one technique to another. The nature of transition was determined and a crossover from second order to first-order magnetic transition was observed with the decrease of crystallite size. Landau theory was performed to confirm the order of magnetic transition of the sample consistent with the Banerjee criterion. The magnetic entropy change (ΔSm) and the relative cooling power RCP, which decreased by reducing the particle size, were calculated.

Quenching of spin-orbit coupling and signature of Griffiths Phase in nanocrystalline La0.6Ba0.4MnO3 perovskite manganite

The size-dependent structural and magnetic properties of nano and bulk samples of 40 ​mol% Ba2+-doped LaMnO3 (i.e., La0.6Ba0.4MnO3) manganite have been investigated in detail. The Rietveld refinement of X-ray diffraction data confirms that nano and bulk La0.6Ba0.4MnO3 manganites crystallize into ideal cubic perovskite structure with Pm3¯m space group. The refined unit cell parameters decrease with increasing calcinations temperature or particle size. The temperature dependent magnetization measurements reveal that both the bulk and nano samples exhibit paramagnetic (PM) to ferromagnetic (FM) phase transition at Curie temperature (TC). A distinct bifurcation between magnetization curves under zero-field cooled (MZFC) and field-cooled (MFC) measurements reveals the possible existence of frustrated magnetic ordering or spin glass clusters. For nano sample, a sharp downward deviation in inverse susceptibility from Curie-Weiss law is observed, which indicates the existence of Griffiths Phase. The analysis of the field dependent magnetization M(H) curves measured at 10 ​K, in terms of saturation moments, reveals that there is a coupling between spin and orbital magnetic moments, in bulk sample of La0.6Ba0.4MnO3 manganite, which can be quenched by reducing particle size of the manganite. According to the Banerjee's criterion, nano sample exhibits first-order magnetic transition and bulk sample shows second-order magnetic transition in the low magnetic field region.

Critical behavior of quasi-2D organic-inorganic halide perovskite (C6H5CH2CH2NH3)2CuCl4 single crystals

Critical behavior of quasi two-dimensional organic-inorganic halide perovskites (C6H5CH2CH2NH3)2CuCl4 is investigated using magneto-thermal and isothermal magnetic properties along the easy axis. Banerjee's criterion indicates that phase transition from paramagnetic to ferromagnetic phases below TC = 9.4 K is of second-order. Scaling analysis reveals that critical exponent β from spontaneous magnetization in the critical region below TC and δ from critical isotherm at TC are found to be 0.22(3) and 9.28–9.4, close to 2D finite XY model. Meanwhile, γ from magnetic susceptibility in the critical region above TC is gradually decreased from 2.4 at high-temperature region. Critical exponents from magneto-thermal properties are found to be consistent with those determined from magnetization isotherms. The reliability of critical values is verified using the scaling hypothesis. Our results evidence that (C6H5CH2CH2NH3)2CuCl4 crossovers from isotropic 2D Heisenberg to anisotropic 3D models towards TC and can be promising candidates for magnetocaloric materials for hydrogen reliquefaction.

Magnetic properties and non-fermi liquid behaviour in mechanically alloyed FeCu

FexCu100−x alloys where x (wt%) = 25, 35, 50, 65, and 75 were prepared via mechanical alloying. Microstructural characterization revealed a single-phase face-centered cubic structure for a wide range of compositions. Atomic volumes were estimated from measured lattice parameters suggesting a high volume state consistent with Weiss model predictions of the ferromagnetic ground state. Saturation magnetic moments at 2 K monotonically decreased from 2.28 μB/Fe for starting Fe powder to 0.65 μB/Fe in Fe25Cu75 alloy. Samples with Fe content higher than 35% exhibited magnetic transition temperatures (Tc) higher than 350 K. On the other hand, the Fe25Cu75 sample exhibit a Tc around 250 K as determined from the gradient method. According to Banerjee's criterion, the magnetic transition is determined to be second order for the Fe25Cu75 alloy. Moreover, modified Arrott plots were used to reveal the critical behavior of the Fe25Cu75. Temperature dependencies of the resistivity were measured for all samples. At low temperatures, the Fe25Cu75 alloy exhibited T3/2 dependence of the resistivity. At higher temperatures (100–300 K) all mechanically alloyed FeCu exhibited unusual T linear dependence resistivity. Such behavior is often called “strange metallicity” or non-Fermi Liquid behavior. The possible origin of such behavior was also discussed.

Structural, magnetic, magnetocaloric properties and critical behavior of La0.6Bi0.1Sr0.3−xCaxMn0.9Cu0.1O3 manganites (with x = 0.1 and 0.15)

The present paper investigates the influence of Ca- doping on the structural, magnetic, magnetocaloric properties and the critical behavior of La0.6Bi0.1Sr0.3−xCaxMn0.9Cu0.1O3 specimens (with x = 0.1 and 0.15). Powder X-ray diffraction revealed the coexistence of rhombohedral (R-3c) and tetragonal (I4/mcm) phases. The temperature dependence of magnetization suggests that samples underwent a ferromagnetic-paramagnetic transition in the vicinity of the Curie temperature (TC). According to the Banerjee criterion, the magnetic phase transition is of a second-order type. The maximum of the magnetic entropy change (-ΔSMmax) was found to be 3.66 J Kg−1 K−1 and 3.74 J Kg−1 K−1 for × = 0.1 and × = 0.15 respectively, under a field change of 5 T. The modified Arrott plot, the Kouvel-Fisher procedure and the critical isotherm were used to determine the critical parameters values of β, γ and δ. All the obtained values of the critical exponent turned out to be close to the value of the theoretical 3D-Ising model. The reliability of the critical exponent was further checked through different methods, such as the Widom scaling relationship and the magnetic equation.