Short-range Ferromagnetic Order Research Articles

Griffiths-like behavior and magnetocaloric properties of rare-earth silicide Tb2Co0.8Si3.2

Novel rare-earth silicide, Tb2Co0.8Si3.2 compound, crystallizes in Lu2CoGa3 structure, a distorted substitution variant of the AlB2 structure. The compound exhibits a complex magnetic state, with a ferromagnetic transition at 58 K, followed by successive antiferromagnetic transitions at 24 K and 8 K, respectively. Isothermal and magnetic hysteresis studies indicate the prominence of competing antiferro and ferromagnetic interactions in the compound. However, this does not lead to the formation of spin glass behavior, as confirmed by AC magnetic susceptibility and heat capacity studies. In the paramagnetic state, the short-range ferromagnetic ordering of cobalt creates a Griffiths-like anomaly that is suppressed at higher magnetic fields. Investigation of magnetocaloric and magnetoresistance properties identifies the compound as a conventional second-order magnetocaloric material with negative magnetoresistance. Furthermore, the determination of Landau coefficients and subsequent analysis indicate that the isothermal entropy change of the compound can be calculated from these coefficients.

Correlation between critical magnetic behavior and griffiths phase in ferromagnetic La0.7Sr0.3Mn1−xFexO3 (x = 0.05) nanoparticle

The magnetic behavior of the La0.7Sr0.3Mn0.95Fe0.05O3 nanoparticles was investigated. X-ray diffraction analysis revealed that this sample exhibited rhombohedral symmetry with space group. The sample underwent a ferromagnetic-paramagnetic transition at approximately 290 K, characterized by a second-order phase transition. Interestingly, the state above the transition temperature is not purely paramagnetic but rather exhibits a short-range ferromagnetic order or Griffiths phase, which becomes more pronounced as the temperature increases up to the Griffiths transition temperature (345 K). The values of the critical exponents obtained in this study, β = 0.671, γ = 1.087, and δ = 2.612, with T C = 290.09 K, are distinct from those of any known universality class, and are confirmed by a single scaling equation of state. This unusual behavior is ascribed to the existence of the Griffiths phase, which reflects the unconventional critical behavior of magnetic susceptibility. In addition to conventional magnetic measurements, detailed studies of isothermal magnetization and magnetocaloric effects have been performed, and theoretical analyses have been utilized to further explore the Griffiths phase. Furthermore, a correlation between the Griffiths phase and the anomalous critical parameters was established.

Role of 5 mol% rare earth (La3+) on the structural, microstructural, and magnetic properties of cobalt chromite ceramics

Spinel oxides, which have the structure AB2O4 and are distinguished by their exceptional magnetic, electric, and multiferroic properties and exhibit a wide range of functional responses in the category of oxides. The cobalt chromate (CoCr2O4) is well-known as a multiferroic-magnetoelctric (ME) material. It belongs to the magnetic spinal oxide family and is noted for its complicated spiral ferromagnetic(FM) orderings. To enhance the magnetic properties of the CoCr2O4, in this work we have chosen Lanthanum (La3+) 0.05 mol% doped cobalt chromites (CoCr2O4) nanoparticles. The solution combustion method was utilized to synthesize the nanomaterial, where urea and glucose were used as fuels. The Structural exploration of the Co0.95La0.05 Cr2O4 nanoparticles were clarified using powder X-ray diffraction. To understand the microstructure properties we have carried out high-resolution electron microscopy and it reveals highly porous nature. In FTIR spectra the two main absorption bands at 507 cm−1 and 616 cm−1 were observed which confirm the formation of spinal chromates. The TGA results revealed a slow thermal degradation, and the sample has a thermal stability that is greater than the temperature range tested. Researchers have examined the changes in temperature and magnetic field affected the magnetic properties of materials over time (ZFC & FC). In comparison to the bulk sample, the Curie temperature at which samples transition from a paramagnetic (PM) state to a collinear short-range ferromagnetic (FM) state is significantly lower. This temperature is denoted as TC-98 K deteriorated with time in terms of quality. At low temperatures, there is no magnetic transition that can be identified between the short-range FM order and the long-range spiral spin structure. This is in contrast to the magnetic transitions that can be discovered in bulk. What gives rise to all of the intriguing qualities that have been described above is the presence of weak magnetic frustration, which is very much connected to super-exchange interactions and is found along different paths such as A-O-A, B–O–B, and A-O-B. This presence is what gives rise to all of the intriguing characteristics that have been described above.

Phase transitions in chiral ferromagnets with topological features of electronic structure (on the example of MnSi)

Magnetic and topological electronic (TEP) phase transitions in chiral ferromagnets with the Dzyaloshinskii-Moriya (DM) interaction are considered. We consider the example of a chiral helical ferromagnet MnSi with a large Berry curvature of the Fermi surface. It is shown that the state of the spin subsystem with a ferromagnetic short-range order and with Berry phases arises as a result of a first-order transition from a helicoidal ferromagnetic phase with increasing temperature. This state is characterized by left-handed vortex microstructures and manifests itself through the topological Hall effect. In the region of the paramagnetic short-range order, vortex microstructures of both signs of spin chirality arise, which leads to the experimentally observed pattern of partial chirality. With an increase in temperature, TEP appears in the chiral paramagnetic state due to that the chemical potential leaves the region of the electronic spectrum with Berry curvature. As a result, the local magnetization and chiral interaction of the DM disappear. A quantitative agreement has been obtained between the calculations of the temperature dependence of the spin magnetic susceptibility and experimental data.

Lead-Free Aurivillius Phase Bi2LaNb1.5Mn0.5O9: Structure, Ferroelectric, Magnetic, and Magnetodielectric Effects.

Aurivillius phase Bi2LaNb1.5Mn0.5O9, derived from ferroelectric PbBi2Nb2O9 by simultaneous substitution of the A-site and B-site cations, was synthesized using a molten-salt method. Here, we discuss the structure-property relationships in detail. X-ray and neutron diffraction show that Bi2LaNb1.5Mn0.5O9 adopts an A21am orthorhombic crystal structure. Rietveld refinement analysis, supported by Raman spectroscopy, indicates that the Bi3+ ions occupy the bismuth oxide blocks, La3+ ions occupy the perovskite A-site, and Nb5+/Mn3+ ions occupy the perovskite B-site. Ferroelectric ordering takes place at 535 K, which coexists with local ferromagnetic order below 65 K. The cation disorder on the B-site results in relaxor-ferroelectric behavior, and the short-range ferromagnetic order can be attributed to Mn3+/Mn4+ double-exchange. Magnetodielectric coupling measured at 5 K and 100 kHz in a field of 5 T suggests the existence of intrinsic spin-lattice coupling with a magnetodielectric coefficient of 0.20%. These findings will provide significant impetus for further research into potential devices based on the magnetodielectric effect in Aurivillius materials.

Nature of Griffiths phase and ferromagnetic 3d-4f interaction in double-perovskite Dy2CoMnO6

Double perovskites Dy2CoMnO6 (DCMO) was synthesized by a sol-gel method and the structure and magnetic properties were systematically investigated. Both X-ray diffraction and Raman spectrum indicate that double pervoskite DCMO has a monoclinic structure with a space group P21/n. A Griffiths phase is confirmed to be existing in DCMO by the magnetic behaviors, which is significantly different from the behaviors of the non-Griffiths phase of Gd2CoMnO6 (GCMO) recently reported in reference. It is suggested that the origins of the different short-range magnetic orders of them can be attributed to the different 3d-4f exchange interactions in DCMO and GCMO, besides the effect of the unavoidable anti-site disorder, interrupting the long-range ferromagnetic (FM) order of Co2+-O-Mn4+, resulting in the formation of short-range FM order. The effects of A-site rare-earth Re3+ ions on the magnetism of double perovskite Re2Co(Ni)MnO6 are dominated by the combining and competing functions of the radius and the moments of rare earth ions (or the 3d-4f exchange interactions). The FM/AFM coupling is not only related to the most outer 4f electrons of the rare earth ions, but also to the inner 5d/6s orbital electrons.

Effect of Electron Doping on the Crystal Structure and Physical Properties of an n = 3 Ruddlesden–Popper Compound La4Ni3O10

The physical properties of La4Ni3O10 with a two-dimensional (2D)-like Ruddlesden–Popper-type crystal structure are extraordinarily dependent on temperature and chemical substitution. By introducing Al3+ atoms randomly at Ni sites, the average oxidation state for the two nonequivalent Ni cations is tuned and adopts values below the average of +2.67 in La4Ni3O10. La4Ni3–xAlxO10 is a solid solution for 0.00 ≤ x ≤ 1.00 and is prepared by the citric acid method, with attention paid to compositional control and homogeneity at low Al level (x) concentrations. The samples adopt a slightly distorted monoclinic structure [P21/a (Z = 4)], evidenced by peak broadening of the (117) reflection. We report a remarkable effect on the electronic properties induced by tiny amounts of homogeneously distributed Al cations, with clear correspondence between resistivity, magnetization, diffraction, and density functional theory (DFT) data. DFT shows that electronically, there is no significant difference between the nonequivalent Ni atoms and no tendency toward any Ni3+/Ni2+ charge ordering. The resistivity changes from metallic to semiconducting/insulating with increasing band gap at higher Al levels, consistent with results from DFT. The metal-to-metal (M-T-M) transition reported for La4Ni3O10, which is often interpreted as a charge density wave, is maintained until x = 0.15 Al level. However, the temperature characteristics of the resistivity change already at very low Al levels (x ≤ 0.03). A coupling of the M-T-M transition to the lattice is evidenced by an anomaly in the unit cell dimensions. Moreover, there is an excellent correlation between the resistivity and magnetization data shown by the metallic and Pauli paramagnetic regime for La4Ni3–xAlxO10 with x < 0.25. The introduction of the fixed +3 oxidation state of Al atoms randomly at the Ni sites reduces the overall oxidation state of Ni2.67+ by keeping the oxygen stoichiometry unchanged. In addition, the nonmagnetic Al3+ for Ni is likely to block Ni–O–Ni exchange pathways through −Ni–O–Al–O–Ni– fragments into the network of corner-shared octahedra with the emergence of possible short-range ferromagnetic ordering of the ferromagnetic domains/clusters that are formed due to Al substitutional disorder in a paramagnetic insulating matrix.

Disorder magnetic behavior of Zn-substituted Cu1-xZnxFe2O4 spinel ferrites

A series of Zn-substituted Cu1-xZnxFe2O4 (where x = 0.0–1.0 with step of 0.1) ferrites were synthesized by double sintering solid state reaction method to explore disorder magnetic behavior. The room temperature (300 K) and low temperature (5 K) magnetic behavior has been analyzed using M-H curve, B–H loop, μi-T curve and M-T curve. The saturation magnetization for sample x = 0.0 to 0.6 and non-saturation magnetization for sample x = 0.7 to 1.0 designate the existence of long-range and short-range ferromagnetic order respectively. The Curie temperature has been derived from the sharp fall of permeability for sample x = 0.0–0.6 which is declining with raising Zn content due to redistribution of cations and weakening of A-B exchange interaction. The shrinking of coercivity affirms softer nature which can be used as high frequency soft magnetic materials. For M-T curve, when temperature is lowered from 300 K to 5 K, different disorder magnetic transition such as paramagnetic-ferromagnetic-reentrant spin glass-spin glass has been remarked for sample x > 0.6. All these feature of magnetic behavior of Cu–Zn ferrites has been studied in details in this paper.

Short-range ferromagnetic order due to Ir substitutions in single-crystalline Ba(Co1− x Ir x )2As2 (0 ⩽ x ⩽ 0.25)

The ternary-arsenide compound BaCo2As2 was previously proposed to be in proximity to a quantum-critical point where long-range ferromagnetic (FM) order is suppressed by quantum fluctuations. Here we report the effect of Ir substitutions for Co on the magnetic and thermal properties of Ba (0 ⩽ x ⩽ 0.25) single crystals. These compositions all crystallize in an uncollapsed body-centered-tetragonal ThCr2Si2 structure with space group I4/mmm. Magnetic susceptibility measurements reveal clear signatures of short-range FM ordering for x ⩾ 0.11 below a nearly composition-independent characteristic temperature T cl ≈ 13 K. The small variation of T cl with x, thermomagnetic irreversibility between zero-field-cooled and field-cooled magnetic susceptibility versus T, the occurrence of hysteresis in magnetization versus field isotherms at low field and temperature, and very small spontaneous and remanent magnetizations <0.01 μ B/f.u. together indicate that the FM response arises from short-range FM ordering of FM spin clusters as previously inferred to occur in Ca(Co1−x Ir x )2−y As2. Heat-capacity C p(T) data do not exhibit any clear feature around T cl, consistent with the very small moments of the FM clusters. The C p(T) in the paramagnetic temperature regime 25–300 K is well described by the sum of a Sommerfeld electronic contribution and Debye and Einstein lattice contributions where the latter lattice contribution suggests the presence of low-frequency optic modes associated with the heavy Ba atoms in the crystals.

Structural and magnetic properties of the layered perovskite system Sr2−xPrxCoO4 (x = 0.7, 0.9, 1.1)

We report the detailed structural and temperature dependent magnetic properties of well characterized, polycrystalline samples of Sr2−xPrxCoO4 (x = 0.7, 0.9, 1.1), in the temperature range 5 K–300 K. In Sr2−xPrxCoO4 (0.7 ≤x≤ 1.1), short range or long range ferromagnetic (FM) order appears below TC~ 150 K. In general the low temperature magnetic state is a mixture of FM, paramagnetic (PM) and antiferromagnetic (AFM) matrices. The spin glass phase (SG) is observed in Sr1.1Pr0.9CoO4 below Tf = 15 K due to comparable strengths of FM and AFM interactions. With increasing x, the Jahn-Teller distortion weakens the FM interaction and AFM interaction starts dominating. Isothermal remanent magnetization (IRM) as a function of time (t) shows that the relaxation mechanism is associated with the interfaces between different types of magnetic matrices.

Relationship between magnetic ordering and gigantic magnetocaloric effect in HoB2 studied by neutron diffraction experiment

Recently, ${\mathrm{HoB}}_{2}$ was discovered to undergo a gigantic magnetic entropy change; the largest $|\mathrm{\ensuremath{\Delta}}{S}_{M}|=40.1\phantom{\rule{0.16em}{0ex}}\mathrm{J}\phantom{\rule{0.16em}{0ex}}{\mathrm{kg}}^{\ensuremath{-}1}\phantom{\rule{4pt}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$ ($0.35\phantom{\rule{0.16em}{0ex}}\mathrm{J}\phantom{\rule{0.16em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}\phantom{\rule{4pt}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$) in magnetocaloric materials studied for hydrogen liquefaction [P. Baptista de Castro et al., NPG Asia Mater. 12, 35 (2020)]. In this study, in order to investigate the origin of the gigantic $|\mathrm{\ensuremath{\Delta}}{S}_{M}|$ in ${\mathrm{HoB}}_{2}$, we studied the magnetic orderings by neutron diffraction with an enriched powder sample of ${\mathrm{Ho}}^{11}{\mathrm{B}}_{2}$. Our experimental results showed the onset of ferromagnetic long-range order below ${T}_{C}=15\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. For the second phase transition at ${T}_{2}=11\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, the spin reorientation occurs, and the temperature dependence of the total magnetic moment of ${\mathrm{Ho}}^{3+}$ shows a kink anomaly, which is typically seen in compounds with quadrupolar ordering. In addition, the temperature dependence of the ferromagnetic short-range order above ${T}_{C}$ is strongly related to that of the magnetic entropy change in ${\mathrm{HoB}}_{2}$. These results infer that the gigantic $|\mathrm{\ensuremath{\Delta}}{S}_{M}|$ in ${\mathrm{HoB}}_{2}$ is caused by (i) the spin reorientation transition, which is likely associated with quadrupolar ordering, giving the additional contribution to $|\mathrm{\ensuremath{\Delta}}{S}_{M}|$ at the lower phase transition temperature, ${T}_{2}=11\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, and (ii) the large FM fluctuation above ${T}_{C}$ with origins in the strong suppression of the FM long-range order.

Pressure-induced incommensurate antiferromagnetic order in a ferromagnetic B -site ordered double-perovskite Lu2NiMnO6

We have investigated the pressure effect on magnetic ordering of the ferromagnetic double perovskite ${\mathrm{Lu}}_{2}{\mathrm{NiMnO}}_{6}$ by magnetization, ac magnetic susceptibility, and neutron diffraction experiments up to 8.0 GPa in order to understand the ferromagnetic-to-antiferromagnetic phase transition by substitution of the $A$ sites in ${A}_{2}{\mathrm{NiMnO}}_{6}$ from rare-earth to indium or scandium ions. Strong ferromagnetic spin correlation seen in the susceptibility at low pressure is significantly suppressed by increasing pressure. In a neutron diffraction experiment, the magnetic Bragg reflections associated with ferromagnetic ordering disappear above 4.5 GPa. For the high-pressure region above 4.5 GPa, an antiferromagnetic ordering with long-period incommensurate modulation appears, which is coexistent with ferromagnetic short-range order. From mean-field calculations, we infer that pressure modification of the delicate balance of the competing next-nearest-neighbor exchange interactions between Ni and Ni, or Mn and Mn, plays an important role in the phase transition from ferromagnetic to antiferromagnetic ordering in ${A}_{2}{\mathrm{NiMnO}}_{6}$.

Structural and multiferroic properties in double-layer Aurivillius phase Pb0.4Bi2.1La0.5Nb1.7Mn0.3O9 prepared by molten salt method

A single-phase sample of the Aurivillius compound Pb0.4Bi2.1La0.5Nb1.7Mn0.3O9 was prepared by a molten salt method using K2SO4/Na2SO4 as the flux. The crystal structure, morphology, ferroelectric, and magnetic properties were investigated. Neutron powder diffraction data confirmed a non-centrosymmetric orthorhombic crystal structure with space group A21am and Pb/Bi disorder in the bismuth oxide blocks, Bi/Pb/La disorder on the perovskite A-site, and Nb/Mn disorder on the perovskite B-site. The morphology of the sample showed anisotropic plate-like grains as probed by scanning electron microscopy. The dielectric constant exhibits a transition peak between 600 K and 640 K that depends on frequency, indicating relaxor ferroelectric behavior. Electrical polarization versus applied field loops are unsaturated, with a remnant polarization of 0.43 μC/cm2 at 40 Hz under the maximum electrical field applied of 160 kV/cm. The ferroelectricity originates from the displacement of oxygen atoms in the BO6 octahedra, resulting in a polar structural distortion. Magnetic susceptibility measurements showed the presence of mixed Mn3+ and Mn4+, resulting in short-range ferromagnetic order via double exchange interactions below 33 K. The remnant magnetization (Mr) is 0.01 emu/g at 5 K. This mixed valence of Mn cations is mainly responsible for the high electrical conductivity. Thus, Pb0.4Bi2.1La0.5Nb1.7Mn0.3O9 exhibits coexisting ferroelectric and ferromagnetic properties.

Weak ferromagnetic insulator with huge coercivity in monoclinic double perovskite La2CuIrO6

Insulating ferromagnets with high TC are required for many new magnetic devices. More complexity arises when strongly correlated 3d ions coexist with strongly spin–orbit coupled 5d ones in a double perovskite. Here, we perform the structural, magnetic, and density functional theory (DFT) study of such double perovskite La2CuIrO6. A new P21/n polymorph is found according to the comprehensive analysis of x-ray, Raman scattering and phonon spectrum. The magnetization reveals a weak ferromagnetic (FM) transition at TC = 62 K and short range FM order in higher temperature range. A huge coercivity is found as high as HC ~ 11.96 kOe at 10 K, which, in combination with the negative trapped field, results in the magnetization reversal in the zero field cooling measurement. The first principle calculations confirm the observed FM state and suggest La2CuIrO6 of this polymorph is a Mott insulating ferromagnet assisted by the spin–orbit coupling.

Magnetic ground state, field-induced transitions, electronic structure, and optical band gap of the frustrated antiferromagnet GeCo2O4

Systematic studies of magnetic ordering, magnetic-field-induced transitions, electronic structure, and optical properties of the frustrated spinel ${\mathrm{GeCo}}_{2}{\mathrm{O}}_{4}$ (GCO) are reported. Our results reveal that GCO orders antiferromagnetically (AFM) at ${T}_{\mathrm{N}}=20.4$ K but with significant short-range ferromagnetic (FM) order up to $T$ $\ensuremath{\sim}5\phantom{\rule{0.16em}{0ex}}{T}_{\mathrm{N}}$. The paramagnetic susceptibility ($\ensuremath{\chi}$) fits the modified Curie--Weiss law, $\ensuremath{\chi}={\ensuremath{\chi}}_{\mathrm{o}}$ + $C$/($T\ensuremath{-}$ $\ensuremath{\theta}$), with $\ensuremath{\theta}=+51$ K for 100 K $T800$ K. The fit to high-temperature-series expansion of $\ensuremath{\chi}(T$) yields J${}_{1}$/${\mathrm{k}}_{\mathrm{B}}=14.7$ K as the dominant FM exchange coupling for the pyrochlore lattice of ${\mathrm{Co}}^{2+}$ spins consisting of alternate planes of Kagom\'e (KGM) and Triangular (TRI) spins lying perpendicular to [111] direction. From the analysis of the M-H plots at 2 K and published results, three critical fields are identified: ${H}_{d}\ensuremath{\sim}11$ kOe due to AFM domains, ${H}_{C1}\ensuremath{\approx}$ 44 kOe related to spin-flips and FM ordering of the TRI spins, and ${H}_{C2}\ensuremath{\approx}97$ kOe related to FM ordering of the KGM spins. For $H$ g ${H}_{C2}$, GCO is a forced ferromagnet with some canting of the spins. Magnetic field dependence of ${T}_{\mathrm{N}}$ follows the relation ${T}_{\mathrm{N}}(H)={T}_{\mathrm{N}}$(0)--${D}_{1}{H}^{2}$ valid for antiferromagnets with ${D}_{1}=6.63\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}$ K/${\mathrm{Oe}}^{2}$. This magnitude of T${}_{\mathrm{N}}$(H) along with the temperature dependence of H${}_{d}$, H${}_{C1}$, and H${}_{C2}$ are used to construct the H-T phase diagram. From the magnitudes of the Curie constant ($C$) and the saturation magnetization at 2 K it is shown that ${\mathrm{Co}}^{2+}$ ions in GCO have the ground state with effective spin $S$ = 1/2. High resolution x-ray photoelectron spectra of 2p and 3d orbitals of Co and Ge confirm the divalent and tetravalent electronic states of Co and Ge, respectively, in GCO. The energy band gap (${E}_{g}=3.28$ eV) evaluated using DFT+U calculations is in good agreement with the experimental results (${E}_{g}=3.16$ eV) obtained from the diffuse reflectance spectroscopy.

Pf-hybridization and magnetic phase transitions in ferromagnetic superconductors

Abstract In the framework of the Anderson pf-model, magnetic phase transitions in 5f-ferromagnetic superconductors with hybridization of localized (f-) and delocalized (p-) electrons are discussed. We consider a free-energy functional containing a contribution due to the mode-mode coupling spin fluctuations. The calculated p-T-diagram of magnetic states describes transitions of the first and second order and the region of the ferromagnetic short-range order too. It is shown that when the temperature and pressure change, a shift of the chemical potential to the pseudogap region is possible, with a jump-like increase in the occupation of the spin-symmetrized electronic states and an increase in the screening of the local magnetic moments.

Critical Behavior of Ni-doped La0.7Sr0.3MnO3 Ceramics

The effect of Ni substitution on the magnetic properties and the critical behavior of La0.7Sr0.3Mn1−xNixO3 compounds, which were prepared by the solid-state reaction method has been investigated. Based on our investigations of the temperature and the magnetic field dependences of magnetization M(T, H) data, it is shown that the Curie temperature ( $$ T_{\rm{C}}$$ ) of La0.7Sr0.3Mn1−xNixO3 compounds will be shifted toward room temperature with increasing Ni concentration (x), $$T_{\rm{C}}$$ = 359–307 K for x = 0.0–0.1. By using the modified Arrott plots and the Kouvel–Fisher methods together with $$M(H,T)$$ data in the vicinity of the ferromagnetic (FM)–paramagnetic phase transition, the critical exponents (β, γ, and δ) have been determined. Our results show the existence of a short-range FM order in the undoped sample (x = 0). The values of β, γ, and δ will be shifted gradually toward those of the mean-field theory when x increases, suggesting that the long-range FM order is favored in Ni-doped samples. The results calculated on the effective exponents of $$\beta_{\rm{eff}} (\varepsilon )$$ and $$\gamma_{\rm{eff}} (\varepsilon )$$ in the asymptotic region indicate the existence of a magnetic disorder in all the samples.

Tunable half-metallicity and edge magnetism of H-saturated InSe nanoribbons

We report on a theoretical study of electronic and magnetic properties of hydrogen-saturated InSe nanoribbons (H-ZISNs). Based on hybrid-functional first-principles calculations, we find that H-ZISNs exhibit tunable half-metallicity and short-range ferromagnetic order. We first show that p-type doping turns narrow H-ZISNs from semimetal to half-metal with spin-polarization along In-terminated edge. This behavior is further analyzed in terms of a two-band tight-binding model, which provides a tractable description of the H-ZISN electronic structure, and serves as a starting point for the determination of magnetic interactions. The dominant exchange interaction determined within the Heisenberg model is found to be ferromagnetic independently of the ribbon width and charge doping. Short-range stability of magnetic order is assessed in terms of the zero-field spin correlation length, which is found to be about 1 nm at liquid nitrogen temperatures. Finally, by calculating spin-dependent transport properties, we find a doping regime in which strongly spin-selective electrical conductivities can be observed. Our findings suggest that H-ZISNs are appealing candidates for the realization of spintronic effects at the nanoscale.

Hirschfeld surface analysis and short-range ferromagnetic ordering in La0.5Ca0.4Ag0.1MnO3 based on critical behavior study

We investigated the Hirschfeld surface analysis and critical behaviour in La0.5Ca0.4Ag0.1MnO3 near the second-order ferromagnetic phase transition at Curie temperature TC. We determined the critical exponents, β, γ and δ corresponding to the temperature dependence of spontaneous magnetization, initial susceptibility and isothermal magnetization, respectively. The study of Hirshfeld surface reflects that both the electrostatic and intermolecular interactions are short range. The values for critical exponents obtained from magnetic measurements are very close to those predicted by the mean field tri-critical model. The critical-exponent values deduced here were in a good conform to those obtained using the modified Arrott plot and Widom scaling relation.

Critical properties and field dependence of the magnetic entropy change in Pr0.8K0.2MnO3 ceramic: A comparison between solid-solid state and sol-gel process

We have performed a systematic study of the critical properties of Pr0.8K0.2MnO3 manganite synthesized using two various methods in the vicinity of the ferromagnetic–paramagnetic phase transition. Our compound was successfully prepared by using the solid state reaction at high temperatures and Pechini sol-gel method. The X-ray diffraction pattern shows that all our samples adopt an orthorhombic structure with Pnma space group. Moreover, the critical exponents β, γ and δ are estimated through various techniques such as the modified Arrott plot, the Kouvel–Fisher method and the critical isotherm analysis founded on the data of the magnetic measurements on record near the Curie temperature. Compared to standard models, the estimated critical exponents are close to the theoretical values of 3D-Heisenberg model for the sample elaborated by solid state reaction and tricritical mean-field model for the sample elaborated by the sol-gel method. These results indicate the presence of a ferromagnetic short-range order in our samples. The calculated values using the Widom scaling equation are proximate to those obtained values from critical isotherm M (TC, µ0H). The accuracy of the critical exponents values was confirmed with the scaling hypothesis, the magnetization curves fall onto two sides independents below and above TC. Interestingly, the change of the universality class is due to the relevant the diminution of grain size. These results imply that the critical behavior of our samples depended sorely on the synthesis technique.