Nature Of Magnetic Transition Research Articles

Magnetism, electrical and thermal transport in R2Ni5C3 (R = La-Nd, Sm, Gd, Tb)

Ternary carbides R2Ni5C3 (R = La-Nd, Sm, Gd, Tb) are the only representatives of the family of interstitial carbides (i.e., compounds with the composition RxTyCz, where T is a transition metal and 2 ≤ (x + y)/z ≤ 4). The crystal structures (space group P4/mbm) of Sm2Ni5C3 [a = 8.26131(7) Å, c = 3.89090(4) Å, RB = 3.2 %, Rp = 1.3 %] and Gd2Ni5C3 [a = 8.24683(4) Å, c = 3.85398(2) Å, RB = 3.9 %, Rp = 3.6 %] are refined for the first time. They are considered to be built by distorted [R8]-cubes incorporating [CNi6]-octahedra condensed with [C2R8]-trigonal bi-prisms. The structural units are characteristic of the CaTiO3- and AlB2-prototypes, respectively. Temperature dependencies of the magnetic susceptibility, specific heat, electrical resistivity, thermal conductivity, and thermopower in the range 1.8 K (2 K) – 300 K are studied. R2Ni5C3 with R = Nd, Sm, Gd, order antiferromagnetically at TN = 3.4, 6.6, and 22.2 K, respectively. The nature of magnetic transitions in Ce2Ni5C3 at Tmag = 2.3 K and Tb2Ni5C3 at 29.4 K requires further clarification. No magnetic orderings for La2Ni5C3 (Pauli paramagnetic) and Pr2Ni5C3 (Curie-Weiss/van Vleck paramagnetic) are detected. Relatively high electrical resistivities and thermal conductivities, together with the small absolute values of Seebeck coefficients, result in poor thermoelectric performance of the R2Ni5C3 carbides. The calculated electronic structure for La2Ni5C3 indicated a rather low density of states at the Fermi level as well as its extreme sensitivity to any doping. The stabilization of the R2Ni5C3 interstitial carbides up to R = Tb is discussed assuming the rigid-band approach as well as the analysis of selected Ni-C interatomic distances.

Nature of magnetic transitions and evidence for magnetoelastic coupling in the biskyrmion-host hexagonal compound MnNiGa

The hexagonal compound MnNiGa with Ni2In-type structure has emerged as an important biskyrmion-host system in which these textures are super-stable over a wide temperature range extending from 16 K to the Curie temperature TC ∼350 K under moderate fields. Both the intensity of the external magnetic field and the presence of magnetoelastic coupling are known to play key role in the stability of the skyrmionic textures. Here we present the results of the first comprehensive investigation of the order of the phase transitions and its field dependence along with magnetoelastic (i.e., spin-lattice) coupling using a combined magnetization and high-resolution synchrotron x-ray powder diffraction (SXRPD) study of MnNiGa. The temperature dependence of the magnetization M(T) exhibits a paramagnetic to collinear ferromagnetic (FM) transition at TC (∼347 ± 0.5 K) with thermal hysteresis and negative slope in the Arrott plots across the TC suggesting its first order character. The M(T) plot in the collinear FM phase exhibits an anomalously decreasing behaviour after reaching its peak value at 300 K followed by a step-like change below 210 K due to an additional spin reorientation transition (SRT) to a non-collinear FM phase with TSRT∼200 ± 1 K. The SRT also shows thermal hysteresis characteristic of a first order phase transition. Our field dependent studies reveal stabilization of the collinear FM phase to higher temperatures and destabilization of the SRT transition setting an upper limit on the magnetic field for the observation of biskyrmions in this system. The Rietveld analysis of the SXRPD data reveals anomalies in the unit cell parameters at TC and TSRT without any change in the crystal symmetry. The modelling of the temperature dependence of the unit cell volume in terms of the Debye-Grüneisen equation reveals significant deviation from phonon contributions and the presence of the quadratic spin-lattice coupling below the FM TC, in the precursor SRT regime as well as below TSRT. The present results on the magnetoelastic coupling in the hexagonal MnNiGa may provide the necessary insight towards understanding the extreme sensitivity of the magnetic skyrmionic textures to external stresses.

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.

Critical behavior and its correlation with magnetocaloric effect in amorphous FexNi80-xB12Si8 alloys with (x = 2.4, 8 and 16)

We study the critical exponents in amorphous FexNi80-xB12Si8 alloys with (x = 2.4, 8 and 16) around ferromagnetic (FM) to paramagnetic (PM) phase transition temperature. The melt spinning method has been used to synthesize the amorphous alloy. The magnetic transition nature undergoes a second-order magnetic phase transition from ferromagnetic to paramagnetic states. The critical exponents were analyzed utilizing the modified Arrott plot technique (MAP), the Widom scaling relation (WSR), and the critical isotherm analysis (CIA). Besides, a separate analysis of the critical performance is presented in terms of the magnetocaloric effect (MCE). It was found to be in line with the conclusion drawn from magnetization data analysis. The determined critical exponent values were found to be consistent and comparable with those predicted by mean field approach. This result emphasizes that the ferromagnetic exchange interaction is of the long range type.

A study on spin memory, nature of magnetic transition, and magnetocaloric effect in Nd0.5Ca0.5MnO3

Current work focuses on the magnetization and magnetocaloric properties of Nd0.5Ca0.5MnO3 (NCMO) prepared by the solid-state reaction method. Belov-Arrott plots indicate a glimpse of first-order magnetic transition. Besides the metamagnetic transition at lower temperatures, NCMO exhibits interesting spin memory property at 4 K. Magnetic entropy change (ΔS) during magnetization attains a peak value of ΔSmax = 15.02 JKg-1K−1 at 20 K for a 14 T magnetic field. But for demagnetization under the same conditions ΔSmax value reduces to 7.20 JKg−1K−1 at 35 K. Demagnetization entropy change is almost constant in the working temperature span compared to magnetization entropy change. The normalized value of ΔS for both magnetization and demagnetization deviates from the universal behavior, which confirms the first-order magnetic transition.

Magnetic and magnetocaloric properties in amorphous CexNi1-x thin films (0.12 ≤ x ≤ 0.43)

We investigate the influence of Ce substitution on the magnetic and magnetocaloric properties in CexNi1-x amorphous alloys with x = 0.12, 0.34 and 0.43, synthesized using ultrahigh vacuum evaporation method. The Ni magnetic moment decreases from 0.033µB, 0.0087µB to 0.002µB when Ce content increases from 0.12, 0.34 to 0.43. The same trend was found for Curie temperature TC which decreases from 40 K, 12 K to 2 K. The magnetic behavior and the magnetic transition were analyzed using Landau theory around the transition temperature. The magnetic transition nature is of a second order from ferromagnetic to paramagnetic state. Good agreement was found between the magnetic entropy (−ΔSM) values estimated by Landau theory and those obtained using classical Maxwell relation.

Magnetic, Magnetocaloric, and Critical Exponent Properties of Layered Perovskite La1.1Bi0.3Sr1.6Mn2O7 Prepared by Coprecipitation Method

The objective of the present work is to investigate the critical behavior and the magnetocaloric performance of the La1.1Bi0.3Sr1.6Mn2O7 double-layered perovskite, prepared by coprecipitation method, around the ferromagnetic (FM)-paramagnetic (PM) phase transition. Using Landau formalism, we have confirmed that the magnetic transition nature is of second-order with a Curie temperature of 340 K. The magnetic entropy values (−∆SM) estimated by Landau theory are in conformity with those obtained using the classical Maxwell relation. The critical exponents have been obtained using various techniques such as modified Arrott plots (MAP), Kouvel-Fisher (KF), critical isotherm analysis (CIA), and Windom scaling relation (WSR). β, γ, and δ are close to the theoretical prediction of the mean-field model, indicating that the magnetic interactions are of a long range. Besides, an independent analysis of the critical behavior is presented in terms of the magnetocaloric effect supporting the validity of the mean-field approach.

The analysis of magnetocaloric effect and magnetic critical behavior in Mn5Ge3−xAgx compounds

Structure, critical behavior and magnetic properties of Mn5Ge3−xAgx compounds with x = 0 and 0.1 have been investigated. With the substitution of Ge by Ag, the Curie temperature decreases from 299.8 to 295.1 K. Investigations for isothermal magnetization curves by Arrott curves, the Landau theory and phenomenological universal curves reveal that this system undergoes a second-order phase transition. To investigate the nature of magnetic transition, a detailed critical parameter study obtained by modified Arrott plots, Kouvel-Fisher method, and critical isothermal analysis has been performed. In comparison with the values given by standard models, these obtained critical parameters suggest a 3D long-range magnetic coupling with the exchange distance decaying as J(r) ≈ r−4.57 and J(r) ≈ r−4.67 for Mn5Ge3 and Mn5Ge2.9Ag0.1.

Magnetic, magnetocaloric properties and phenomenological model in amorphous Fe40Ni38Mo4B18 alloy

We investigate in detail the magnetic, magnetocaloric properties and phenomenological model of amorphous Fe40Ni38Mo4B18 alloy. The melt spinning method has been used to synthesize the amorphous alloy. With a Curie temperature of 610 K, the magnetic transition nature undergoes a second-order magnetic phase transition from ferromagnetic to paramagnetic states. The magnetic entropy change (-ΔSM) is determined using the thermodynamic Maxwell’s relation. Moreover, we report a theoretical investigation of the magnetocaloric effect using a phenomenological model. The best model parameters and their variation with temperature and the magnetic field were obtained. The theoretical predictions were found to be in line with the experimental results.

Structural and magnetic properties of La1-x⎕xMnO3 (x = 0.1; 0.2 and 0.3) manganites

The intrinsic objective of this work is to investigate the structural (RX, MEB, TGA and IR) and magnetic properties of La1 La1-x⎕xMnO3 (x = 0.1; 0.2 and 0.3) series prepared through the sol–gel method. All these systems crystallize in the rhombohedral structure, $$ {{\rm R}\bar{3}{\rm c}} $$ space group, with the presence of a secondary phase for x = 0.3. We recorded the increase of a unit cell volume when the La deficiency amount increases, which refers to the fact that the vacancy is characterized by a radius other than zero. Another point that can be quoted is the increase of Mn–O–Mn bond angle and the decrease of Mn–O length with lanthanum deficiency (x), confirming the increase of the unit cell volume. The evaporation of water rose by the weight loss as a function of temperature in all samples. The FT-IR measurement revealed one peak corresponding to the Mn–O bond; this can be explained by the Jahn–Teller effect where the Mn ion makes an internal movement against the MnO6 octahedron. The thermal variation of the magnetization indicates the existence of a paramagnetic–ferromagnetic transition at Curie temperature with the increase of lanthanum deficiency. Saturation magnetization and Curie temperature increased with x (0.1; 0.2 and 0.3) deficiency. Hysteresis cycles confirm the ferromagnetic character at low temperatures and paramagnetic state with temperature increase. The increase of saturation magnetization can be accounted for in terms of the change of high spin Mn3+ to low spin Mn4+. Departing from the study of magnetic properties in terms of Arrott plots, the nature of magnetic transitions proves to be of second order.

Magnetic, magnetocaloric and critical exponent properties of amorphous [formula omitted] ribbons prepared by melt-spinning technique

Amorphous Fe67Y33 ribbons were prepared using melt-spinning method and their magnetic, magnetocaloric and critical exponent properties were investigated. The magnetocaloric behavior and the magnetic transition were analyzed in terms of Landau theory around the transition temperature. Good agreement was found between the magnetic entropy (-ΔSM) values estimated by Landau theory and those obtained using classical Maxwell relation. The magnetic transition nature is of a second order from ferromagnetic to paramagnetic states with a Curie temperature of 240 K. Through various techniques such as modified Arrott plots (MAP), Kouvel–Fisher (KF), critical isotherm analysis (CIA) and Windom scaling relation (WSR); the critical exponents (β, γ and δ) were found to be close to those of the long-range mean-field approach. In addition, an autonomous analysis of the critical behavior is presented in terms of the magnetocaloric effect confirming the validity of the mean-field approach.

Magnetic field dependence of Griffith phase and critical behavior in La0.8Ca0.2MnO3 nanoparticles

In this work, the La0.8Ca0.2MnO3 nanoparticles of ∼30 nm were prepared by a sol-gel method, and their magnetic properties were investigated. The sample shows a paramagnetic-to-ferromagnetic phase transition at about 214 K. The Griffiths phase, which is identified by the downturn of the inverse susceptibility versus temperature plot from the Curie-Weiss law, is suppressed with the increase of the applied magnetic field strength such as 10 kOe. From the study of magnetic properties in terms of Arrot plots, the nature of magnetic transitions is found to be of second order. The critical behavior of La0.8Ca0.2MnO3 nanoparticles was studied around its Curie temperature. The estimated critical exponents were close to those expected for mean-field model. These critical exponents fulfill the Widom scaling relation, implying the reliability of our values.

Influence of K addition on the magnetic and magnetocaloric properties of La2-xKxNiMnO6 (x = 0, 0.2 and 0.4) double perovskite

The structural and magnetic properties of La2-xKxNiMnO6 (x = 0, x = 0.2 and x = 0.4) synthesized by a sol gel method have been investigated. Refinements of X-ray diffraction data reveal that our compositions crystallized in monoclinic structure with P21/n space group. Double magnetization transition are observed from the magnetization measurements versus temperature (TC1 at high temperature and TC2 at low temperature) and can be ascribed to Ni2+-O-Mn4+ and Ni3+-O-Mn3+ superexchange interactions, respectively. Based on Banerjee criterion, the nature of magnetic transition is of second order for all synthesized samples. The magnetic entropy change was calculated from the measurement of isothermal magnetization versus magnetic field at different temperatures. The maximum (−ΔSMmax) under a magnetic field of 5 T is found to be 1.17 J/kg K, 1.10 J/Kg and 0.96 J/Kg K for x = 0, x = 0.2 and x = 0.4, respectively. The relative cooling power (RCP) increases with K doping and reaches 173 J/kg for x = 0.4.

The influence of Cr and Ni on the character of magnetic phase transition in LaFe11.52-xMxSi1.48 alloys

The critical content of the substitution element M for Fe in LaFe11.52-xMxSi1.48 (M=Ni/Cr) alloys was studied. When the content exceeds the critical content of the element M, the nature of magnetic transition of the alloy changes from first order to second. And the relationship between phase formation and magnetic properties in LaFe11.52-xMxSi1.48 (M=Ni/Cr) alloys near critical value of Ni/Cr has been discussed sufficiently. The critical content of Ni element is x=0.08 and that of Cr is x=0.25. With the increase of Cr content, the α-Fe grows up obviously in LaFe11.52-xCrxSi1.48 alloys. The impact of partial substitution of Ni for Fe is superior to that of Cr on the magnetic properties of 1:13 phase. The substitution elements and the content of those elements have different effects on the nature of magnetic transition and magnetic entropy changes of LaFe11.52-xMxSi1.48 alloys.

Tuning the magnetic and structural transitions in TbCo2Mnx compounds

The wide ranging magnetic behavior in intermetallic compounds continues to attract broad interest. Effective control of their magnetic properties is of great importance for fundamental research and potential applications. In this work the structural and magnetic properties of $\mathrm{TbC}{\mathrm{o}}_{2}\mathrm{M}{\mathrm{n}}_{x}$ compounds are studied by a combination of temperature dependent synchrotron x-ray diffraction, neutron powder diffraction, specific heat, and magnetic measurements. Magnetization measurements show that the addition of Mn can modify the magnetic behavior significantly: first, the magnetic transition temperatures increase from \ensuremath{\sim}227 K to 332 K with $x=0.0\phantom{\rule{0.28em}{0ex}}\mathrm{to}\phantom{\rule{0.28em}{0ex}}0.3$; secondly, the nature of the magnetic transitions change from the first order to second order, as identified by three methods (Banerjee criterion, master curves of magnetic entropy changes, and detailed crystal structure analysis through neutron diffraction). Both synchrotron x-ray diffraction and neutron diffraction confirm that a structural transition, from cubic $Fd\overline{3}m$ to rhombohedral $R\overline{3}m$ on cooling, occurred accompanying the magnetic transition. To further clarify the nature of the second order magnetic phase transitions, we have carried out a detailed critical exponent analysis. The derived critical exponents are close to the theoretical prediction from the mean-field model, indicating the magnetic interactions are long range. This work benefits our general understanding of magnetic interactions in intermetallic compounds and provides guidance to design a functional magnetic material for room temperature magnetic devices.

Magnetic and universal magnetocaloric behavior of rare-earth substituted DyFe0.5Cr0.5O3

We report the effect of partial substitution of Dy-site by rare-earths (R=Gd, Er and La) on the magnetic and magnetocaloric behavior of a mixed metal oxide DyFe0.5Cr0.5O3. Structural studies reveal that substitution of Dy by R has a minimal influence on the crystal structure. Magnetic and heat capacity studies show that the magnetic transition around 121K observed for DyFe0.5Cr0.5O3 remains unchanged with rare-earth substitution, whereas the lower magnetic transition temperature is suppressed/enhanced by magnetic/non-magnetic substitution. In all these compounds, the second order nature of magnetic transition is confirmed by Arrott plots. As compared to DyFe0.5Cr0.5O3, the values of magnetic entropy change and relative cooling power are increased with magnetic rare-earth substitution while it decreases with non-magnetic rare-earth substitution. In all these compounds, magnetic entropy change follows the power law dependence of magnetic field and the value of the exponent n indicate the presence of ferromagnetic correlation in an antiferromagnetic state. A phenomenological universal master curve is also constructed for all the compounds by normalizing the entropy change with rescaled temperature using a single reference temperature. This master curve also reiterates the second order nature of the magnetic phase transition in such mixed metal oxides.

Magnetocaloric effect and nature of magnetic transition in low dimensional DyCu2

In this manuscript, we propose a method to prepare small flakes of DyCu2. On top of that we also report on the magnetocaloric effect and nature of magnetic transition of a strongly anisotropic DyCu2 in its low dimension. Magnetization measurements were carried out in the temperature range of 5–100 K and up to the maximum magnetic field strength of 50 kOe. Magnetic entropy change (ΔSM) is estimated using the well-known Maxwell’s equations and is found to be −4.31 J/kg-K. Indeed, the ΔSM peak broadened marginally compared with its bulk DyCu2 and such a broadening can be attributed to significant increase in the total grain boundary volume. As these small flakes consists larger ΔSM values at temperatures higher than the Nèel temperature (TN), one can use them as a magnetic refrigerant material in a broad temperature range. We also plotted the M2 vs. H/M (which are called as the Arrott plots) in order to find the nature of magnetic transition. Arrott plots infer that indeed there exists nonlinearity in M2 vs. H/M behavior and such nonlinear behavior is ascribed to the random anisotropy or a random field that is present in the system.

Effect of cobalt on structural, magnetic and magnetocaloric properties of La0.8Ba0.1Ca0.1Mn1-xCoxO3 (x = 0.00, 0.05 and 0.10) manganites

We have studied the effect of Co substitution on the structural, magnetic and magnetocaloric (MCE) properties of La0.8Ba0.1Ca0.1Mn1-xCoxO3 compounds with x = 0.00, 0.05 and 0.10. All samples were synthesized using polymerization complex sol-gel method. X-ray diffraction (XRD) studies show that all compositions crystallize in the rhombohedral structure with the R3¯c space group. Rietveld analysis indicates that each (Mn, Co)O6 octahedron has a little distortion and that the θ(Mn, Co)O(Mn, Co) bond angles decreases with increasing Co content. The zero field cooled (ZFC) and field cooled (FC) magnetizations reveal that all samples undergo a paramagnetic-ferromagnetic (PM-FM) phase transition and a large deviation is usually observed between ZFC and FC curves which is due to the presence of competing FM and antiferromagnetic (AFM) interactions leading to a glassy behavior. The Curie temperature (TC) is found to decrease from 282 K for x = 0.00–214 K for x = 0.10. Arrot’s plots reveal a second order nature of magnetic transition for all samples, which is also confirmed by landau’s theory and universal curves.

Multiple caloric effects in geometrically frustrated “114” CaBaCo4O7 Cobaltite

We have investigated the magnetocaloric and electrocaloric effects in “114” CaBaCo4O7 (CBCO) sample prepared by solid state method. Magnetization study has revealed the ferrimagnetic transition (TC) at 60K and another transition at 66K. Observation of irreversibility and first order nature of magnetic transition above TC has suggested a complicated magnetic nature of the system. A maximum magnetic entropy change of ~6.8J/Kg-K has been found at TC and further a broadening of the entropy peak with the increase of magnetic field indicates the field induced transition above TC. From temperature dependent pyrocurrent measurements, we have measured the electric polarization under different electric fields and the change in isothermal electrocaloric entropy is found to be ~0.50J-m−3K−1 (for 150kV/m) just above magnetic transition temperature.

The effect of boron doping on crystal structure, magnetic properties and magnetocaloric effect of DyCo2

The magnetic properties and magnetic entropy changes of DyCo2Bx (x=0, 0.05, 0.1, and 0.2) alloys were investigated. The Curie temperature (TC) increases with increasing B concentration. The frequency dependence of ac magnetic susceptibility of DyCo2 caused by the narrow domain wall pinning effect is depressed by B doping, but the coercivity and the magnetic viscosity are prominently increased in the B doped alloys. The magnetic transition nature of DyCo2Bx changes from the first-order to the second-order with increasing x, which leads to the decrease of the maximum magnetic entropy change. However, the relative cooling power (RCP) of DyCo2 and the B doped alloys remains nearly constant.