Short-range Magnetic Interactions Research Articles

Hydrogen-annealing modulated magnetocaloric effect and critical behavior of Weyl semimetallic Co3Sn2S2

Modulating the electron interaction and magnetic domains is an essential strategy to evoke novel physical properties, both for fundamental research and for related magnetic applications. The emerging annealing process attracted attention due to its capability of tuning the magnetic performance, but it has been rarely studied. Herein, we conducted hydrogen annealing on the Weyl semimetallic Co3Sn2S2 and investigated the magnetic interaction, critical behavior, and magnetocaloric effect (MCE). Hydrogen-annealed Co3Sn2S2 (HA-Co3Sn2S2) exhibits a distinct anisotropy-dependent magnetic behavior, where a typical second-order transition with an easy magnetization process is observed under H//c. However, a frustrated magnetic state composed of ferromagnetic (FM), antiferromagnetic (AFM), and/or spin glass phases is observed when H//ab. Critical analyses illustrate that the ground state of HA-Co3Sn2S2 lies between the 3D-Ising model and the Mean-filed model, indicating the presence of both long-range and short-range magnetic interactions in the system. Additionally, we found that HA-Co3Sn2S2 exhibits an enhanced saturation magnetization (Ms) and magnetic refrigeration capacity, both showing anisotropic dependence, compared to the pristine Co3Sn2S2. Our work develops hydrogen annealing to modulate electron coupling and magnetic domains, paving the way for further studies of anisotropic magnetic behavior and applications in magnetic refrigeration.

Local mechanism for magnetoelastic coupling and magnetic frustration in high-pressure synthetized NixTi2S4 intercalated sulfide

The local atomic arrangement correlates to the short-range magnetic interactions mediated by electron hopping between Ni eg states, suggesting the occurrence of magnetoelastic coupling and magnetic frustration in Ni0.8Ti2S4.

Enhanced magnetocaloric effect in melt-spun Mn[formula omitted]Fe[formula omitted]Ge3 (x = 0 and 1) ribbons with anisotropy induced spin-dimensionality crossover

We report the structural, magnetic, magnetocaloric and ferromagnetic resonance properties of melt-spun Mn5−xFexGe3 (x = 0 and 1) ribbons. The melt-spun Mn5Ge3 ribbons exhibit hexagonal structure with preferential growth along c-axis while Fe doping retains the structure but changes preferential growth in in-plane direction. Fe doping enhances the ferromagnetic to paramagnetic phase transition temperature of Mn5Ge3 ribbons. Elaborate isothermal magnetization data analyses in the critical region yield critical exponents β= 0.344(1), γ= 1.284(1) and δ= 4.70(1) with critical temperature TC= 303.64(1) K for x = 0 while β= 0.389(1), γ= 1.334(1) and δ= 4.441(1) with TC= 330.84(1) K for x = 1. Further, the magnetization data in the vicinity of TC satisfies the magnetic scaling equations of state characteristic of a second-order phase transition. The magnetocaloric performance is reflected through maximum entropy change −ΔSmmax(T) ∼ 5.0(2.9) J kg−1 K−1; refrigerant capacity RC ∼ 505(302) J kg−1 and temperature-averaged entropy TEC(10 K) ∼ 4.92(2.28) J kg−1 K−1 at an applied field of 5 T for x = 0(1) ribbons, respectively. −ΔSmmax(T) embracing the critical region is found to be well-described by the critical exponents that are consistent with those determined by the modified Arrott plots and Kouvel–Fisher analyses. Renormalization group calculations further confirm that Mn5Ge3 and Mn4FeGe3 systems behave as 3D Ising and 3D Heisenberg ferromagnets in the critical region wherein short-range extended magnetic interactions decay as J(r) ≈ r−4.995 and r−4.895 with intermoment distance, respectively. Ferromagnetic resonance study reveals that with the introduction of Fe, the magnetocrystaline anisotropy (Ku∼1.4×106 erg/cm3) of Mn5Ge3 gets suppressed so much so that the system exhibits a crossover from 3D Ising to 3D Heisenberg universality class in the critical region.

Critical behavior and room temperature magnetocaloric effect of La-doped Pr0.7Sr0.3MnO3 compounds

In this work, we present the critical and the magnetocaloric properties of Pr0.7-xLaxSr0.3MnO3 compounds around room temperature. The samples exhibit a single phase with an orthorhombic structure. However, the lattice parameters increase with an increase in La content (x). The Curie temperature (TC) of the ferromagnetic (FM)-paramagnetic (PM) phase transition of compounds increases from 256 K for x = 0–319 K for x = 0.3. We observed a large magnetocaloric effect with high maximum magnetic entropy change (|ΔSmax|) values occurring around room temperature, corresponding to |ΔSmax| = 6.65 and 5.21 J/kgK under a magnetic field change (ΔH) of 50 kOe for x = 0.2 and 0.3, respectively. We also pointed out that the change in |ΔSmax| obeys an exponential function of ΔH (|ΔSmax| ∼ ΔHn), where the value of field exponent (n) is approximately 0.52. Furthermore, the critical behavior around TC for compounds with x = 0.2 and 0.3 has been investigated. The results indicate that these compounds undergo a second-order phase transition with the critical parameters (β = 0.311, γ = 1.137, and δ = 4.656 at TC = 298.4 K for x = 0.2; and β = 0.319, γ = 1.098, and δ = 4.442 at TC = 318.7 K for x = 0.3) that are quite close to those expected for the 3D-Ising model. This suggests the existence of the short-range magnetic interactions in these compounds.

Critical behavior in the itinerant ferromagnet SmMn2Ge2

Transition metal and rare earth intermetallics have been a fertile playground for research of various quantum states. We report detailed magnetic studies on SmMn2Ge2, an anisotropic itinerant magnet with multiple magnetic phases. The critical behavior of the ferromagnetic phase transition is investigated by employing the modified Arrott plot with the Kouvel–Fisher method. The critical temperature T C is determined to be around 342.7 K with critical exponents of β = 0.417 and γ = 1.122, and the interaction function is found to be J(r) ∼ r −4.68, suggesting the coexistence of long-range and short-range magnetic interactions. Our results contribute to the understanding of complex magnetism in SmMn2Ge2, which may provide fundamental guidance in future spintronic applications.

Insight into the structural and magnetic properties of RECo12B6 (RE = Ce, Pr, Nd) compounds: A combined experimental and theoretical investigation

Rare earth (RE) based RE-TM-X (TM = transition metal elements; X = P-block elements) materials have received continuous attention due to the exhibition of various intriguing magnetic functional characteristics. In this work, a combined experimental and theoretical investigation has been conducted in detail for RECo12B6 (RE = Ce, Pr, Nd) compounds with regard to their structural and magnetic properties, particularly the magnetocaloric effect and magnetic phase transition (MPT). All of the present RECo12B6 compounds are found to crystalize in the SrNi12B6-type structure and with a ferrimagnetic ground state, which is confirmed by density functional theory calculations and magnetization measurements. The magnetic moments of RE atoms and Co atoms tend to be in antiparallel alignment, and the MPT of these materials originates primarily from the spin-polarized 3d electrons of the Co atoms, which can be greatly affected by the 4f electrons of RE atoms. Considerable magnetocaloric effects have been observed around its own TC of 130, 157, and 160 K, for CeCo12B6, PrCo12B6, and NdCo12B6, respectively, which is related to a typical second-order MPT. The corresponding maximum magnetic entropy change and relative cooling power values,with field changes of 0–70 kOe, are determined to be 2.54, 2.84, and 2.77 J/kg K and 116.8, 156.2, and 155.1 J/kg, respectively. The MPT properties of present RECo12B6 compounds were studied in further detail by critical analysis using the modified Arrott Plot and Kouvel-Fisher methods, which can be explained within the frame of the 3D Heisenberg model with short-range magnetic interaction.

Cyanido-Bridged Heterobimetallic Molecular Squares: Low-Dimensional Models of Prussian Blue Analogues and Beyond

The cyanido-bridged square-like molecules with d/f metal ions occupying the corners of the square are considered molecular models of the Prussian Blue Analogues (PBAs) because they reproduce one face of their 3D face-centered cubic structure, being called low-dimensional PBAs. Such highly regular complexes provide unique insights into the short-range magnetic exchange interaction between the metal ions of PBAs and exhibit magnetic properties which are not found for PBAs. This review focuses on the preparative routes and magneto-structural characterization of d-d(d′)/d-f tetranuclears with a square-like topology generating rich families of molecular switches and nanomagnets. Relevant examples that provided a better comprehension of the magnetic behavior of PBAs, including subtle chemical factors that interfere in the photo- and thermally induced electron transfer are reviewed herein. A special attention is paid to the design of d-f cyanido-bridged squares, less numerous compared to the d-d/d′ ones, that proved to be suitable model compounds for the theoretical treatment of the magnetic exchange interaction between d and f spin carriers across the cyanide ligand. The square-shaped PBAs represent a very active area of research that is enriched yearly with new examples with potential for the development of molecular-scaled electronic devices.

Long- and short-range magnetic interactions in nanocrystalline lightly Cr‑doped manganites

Long- and short-range magnetic interactions in nanocrystalline lightly Cr‑doped manganites

Role of short-range magnetic interaction between core and surface spins in exchange bias and memory effect in nanocrystalline doped manganite

• Synthesis of bulk and nanocrystalline La 0.4 (Ca 0.5 Sr 0.5 ) 0.6 MnO 3 compounds. • Enhancement of ferromagnetic clusters in core part with size reduction is noticed. • Magnetic inhomogeneity induced glassy magnetic phase is observed in nanomaterial. • Magnetic disorder results in strong memory and exchange bias effect in nanocrystal. • Theoretical model for core-shell structure corroborates the short-range correlation. A comparative study of low temperature magnetic properties for bulk and nanocrystalline La 0.4 (Ca 0.5 Sr 0.5 ) 0.6 MnO 3 compounds has been presented here. Considerable enhancement of exchange bias as well as magnetic memory effect in nanocrystalline material has been observed compared to bulk. Substantial increase of ‘A’ -site size-disorder parameter ( σ 2 ) with ‘Sr’ doping concentration in La 0.4 Ca 0.6 MnO 3 compound is found to assist in destabilizing the charge ordering state along with a grow of ferromagnetic clusters in these systems. In nanomaterial, the short-range magnetic interaction between the increased ferromagnetic cluster and the antiferromagnetic matrix in the core part of the core-shell structure assists to develop strong magnetic disorder (glassy phase) in the system. Additionally, the magnetic interaction of uncompensated shell spins and its interaction with adjacent core ferromagnetic clusters also attribute to grow glassy phase in the system, resulting in strong memory effect and exchange bias effect. The experimental findings have been described in terms of different theoretical models developed for core-shell structure.

Magnetocaloric effect near room temperature and critical behaviour of Fe doped MnCo0.7Fe0.3Ge

We report on the critical magnetic behaviour, universality class and magnetocaloric properties of Mn0.7Fe0.3Co0.7Fe0.3Ge. At room temperature, the alloy is found to crystallize in the hexagonal structure of Ni2In-type. Paramagnetic to ferromagnetic phase transition is found to occur at a Curie temperature of about 298 K. The saturation magnetization value at low temperatures is about 2.79 μB/f.u. Kouvel-Fisher and modified Arrott's Plot methods along with magnetocaloric method are implemented to determine the critical exponents which are found to be self-consistent. The critical exponents suggest short range magnetic interactions with 3D-Heisenberg universality class of the alloy as inferred from the relationJ(r)~1/r5.02. Around the Curie temperature, the maximum change in the magnetic entropy, under the influence of 90 kOe, is about −3.91 J kg−1 K−1.

A quasilinear hydrazone-based mononuclear dysprosium compound withC4vsymmetry exhibiting field-induced complex magnetic relaxation

AC4vsymmetrical mononuclear dysprosium(iii) compound has been successfully isolated using a new quasilinear single pyrazinyl hydrazone ligand. Single-ion behavior and the short-range intermolecular magnetic dipolar interaction are essential to the complex magnetic relaxation.

Ferromagnetic thin Films with Simple Cubic Structure as Described by Fourth Order Perturbed Heisenberg Hamiltonian

For the first time, fourth order perturbed Heisenberg Hamiltonian has been applied to study the properties of simple cubic structured ferromagnetic ultrathin films with two spin layers. Only the spin exchange interaction, second order magnetic anisotropy constant and the short-range magnetic dipole interaction were taken into account. Only when the second order anisotropy constant varies from one spin plane to the other spin plane, perturbation becomes nonzero. 3-D plots of total energy versus spin exchange interaction and angle, total energy versus second order anisotropy constant in bottom spin layer and angle, and total energy versus second order anisotropy constant in top layer and angle were plotted. Peaks in the plots are closely packed in fourth order perturbed case compared to the plots obtained using third order perturbed case. All the graphs were plotted using MATLAB program

Enhanced magnetic properties in chemically inhomogeneous Nd-Dy-Fe-B sintered magnets by multi-main-phase process

Homogeneous substitution of Dy for Nd in the hard magnetic 2:14:1 phase can effectively enhance coercivity to ensure the high temperature operation, however, inevitably deteriorate remanence at expense. In this work, we performed a comparative investigation of the two magnets prepared by multi-main-phase (co-sintering Nd2Fe14B and (Nd, Dy)2Fe14B powders) and single-main-phase (sintering (Nd, Dy)2Fe14B powders) approaches. The comparative investigation reveals that at the same Dy substitution level (2.16 wt%), such chemically inhomogeneous multi-main-phase magnet possesses better room-temperature magnetic properties as well as thermal stability than those of the single-main-phase one with homogenous Dy distribution in the matrix grains. Room-temperature magnetic properties Hcj = 1664 kA/m, Br = 1.33 T and (BH)max = 350.4 kJ/m3 for the multi-main-phase magnet are all better than those for the single-main-phase magnet with Hcj = 1536 kA/m, Br = 1.29 T and (BH)max = 318.4 kJ/m3. In addition, over the temperature range from 295 to 423 K, both the temperature coefficients of coercivity and remanence for the multi-main-phase magnet are also lower than that for the single-main-phase magnet. Such superior magnetic performance is attributed to the short-range magnetic interactions inside individual 2:14:1 phase grains and the long-range magnetostatic interactions between adjacent grains with inhomogeneous Dy distribution. Our work provides a feasible approach of enhancing coercivity and retaining energy product simultaneously in the Nd-Dy-Fe-B permanent magnets.

Critical behavior, universality class and magneto-transport properties of Ni2MnIn

Structural, magnetic, transport and critical properties of Ni2MnIn are investigated using the combined results of x-ray diffraction, magnetization and electrical resistivity. Ni2MnIn crystallizes in cubic structure with Fm-3m space group. The alloy is metallic and shows Fermi liquid behavior. Critical exponents are extracted using the modified Arrott’s plot (MAP), Kouvel-Fisher (KF) and magnetocaloric effect (MCE) methods and are found to be mutually consistent. The alloy belongs to the three-dimensional (3D)-Heisenberg universality class with short range magnetic interactions, as inferred from the exchange interaction J (r) ∼ r−4.91. The suppression of spin-fluctuations by the applied magnetic field results in negative magnetoresistance (MR) and negative magnetic entropy change. Collapse of normalized magnetic entropy curves and the normalized magnetoresistance curves onto a single universal curve confirms the second-order nature of the magnetic phase transition.

Observation of R-type ferrimagnetism in the intermetallic Mn1.25Sb

Magnetism in Mn1.25Sb is discussed using the combined results of measured structural and magnetic properties and spin-polarized density functional theory calculations. Mn1.25Sb crystallizes in NiAs-type hexagonal structure, where the Mn-atoms occupy the 2a-sites and 2d-sites. The lattice parameter values are a = b = 4.2134 (1) Å and c = 5.6890 (4) Å. From the dc-magnetization measurements, it was understood that the compound exhibits a typical R-type ferrimagnetic behavior. The total magnetic moment follows predominantly T3/2 behavior up to ~60 K and predominantly T2 behavior above 90 K. The values of critical exponents (β = 0.60 ± 0.01, γ = 1.38 ± 0.04 and δ = 3.32 ± 0.01) indicate that the magnetization conforms to the mean-field theory as well as to the 3D- Heisenberg model with local or short-range magnetic interactions. From the DFT calculations, it was understood that the magnetic moment of Mn-atom at the 2d-site (μMn2d=4.09μB) is aligned antiparallel to the magnetic moment of the Mn-atom at the 2a-site (μMn2a=4.47μB). The exchange interaction strength parameter (J) is found to be positive for μMn2a-μMn2a and negative for the μMn2a-μMn2d confirming the presence of competing magnetic interactions in the system.

Assessment of the critical behavior near the FM to PM phase transition in cubic Ni0.3−xCuxZn0.7Fe2O4 spinel ferrite

In this study, we report a thorough examination of the critical behavior of the cubic Ni0.3−xCux Zn0.7Fe2O4 (x = 0.0, 0.1 and 0.2) spinel ferrite which are crystallized with different irregular shapes of particle size (spherical,polygonal and cubic). The magnetic transition is ferromagnetic to paramagnetic state for all Cu-doped compounds. Different theoretical analyses, as the modified Arrott plot, Kouvel–Fisher method, and critical isotherm, have been used to identify the values of the ferromagnetic transition temperature TC, and the critical exponents of β, γ and δ. All the obtained values of critical parameters were found to be close to the 3D-Heisenberg theoretical model, which implies short-range magnetic interactions in Cu-doped compounds. The reliability of critical parameters was further checked through different methods, such as the Widom scaling relationship and the magnetic equation.

Effect of nonmagnetic substitution on the magnetic correlation of the frustrated Ca3CoMn1-xGaxO6 (0≤x≤0.2)

For the spin-chain compound Ca3CoMnO6, the perfect Co/Mn ionic order causes the lost of ↑↑↓↓ long-range antiferromagnetic order. The lost long-range magnetic order results in the emergence of short range magnetic correlation interaction, forming the so called “order by disorder” phenomenon. In present paper, nonmagnetic Ga3+-doped Ca3CoMn1-xGaxO6 compounds were prepared. The influence of Ga3+ substitution on the structure and magnetic order of Ca3CoMn1-xGaxO6 were investigated. It is found that the solid solubility of Ga3+ cation in Ca3CoMn1-xGaxO6 is 0.2 < x < 0.3. With introducing of Ga3+ cation, the oxidation state of some Co cations changes from Co2+ to Co3+. Magnetization measurements reveal that doped with nonmagnetic Ga3+ weakens the formation of short range magnetic order and enhances the antiferromagnetic transition temperature. As a result, more robust long rang antiferromagnetic order is established and the transition field that causes the ↑↑↓↓ spin state of Co–Mn–Co–Mn chain to ↑↑↓↑ state increases obviously. Meanwhile, the shortened short range magnetic correlation in Ga3+ doped Ca3CoMn1-xGaxO6 can be driven more easily by the thermal activation energy and a quicker dynamic behavior was observed in time windows.

Critical behaviour and magnetocaloric properties of hexagonal MnCo0.7Fe0.3Ge

The structural and magnetic properties of MnCo0.7Fe0.3Ge are investigated using x-ray diffraction and magnetization measurements. The alloy crystallizes in Ni2In-type hexagonal structure with P63/mmc space group and exhibits ferromagnetic ordering at 245 K with a saturation magnetization of about 2.73 μB/f.u. The critical exponents (β = 0.42 ± 0.02, γ = 1.42 ± 0.07, δ = 4.38 ± 0.32) and the critical temperature (TC ∼ 243 K) obtained through Modified Arrott’s plot (MAP) and Kouvel-Fisher (KF) methods are found to be self-consistent. A maximum magnetic entropy change of about ΔSmag = −4.93 J.kg−1.K−1 is noticed under the influence of 90 kOe. The critical exponents which are obtained through magnetocaloric method are in good agreement with those obtained through MAP and KF methods. The exponents indicate 3D-Heisenberg universality class with short range magnetic interaction, as inferred from the exchange interactions J(r) ∼ r−5.04.

The disordered and correlated insulator Bi2CrAl3O9

The $3d$ transition metal insulator ${\mathrm{Bi}}_{2}{\mathrm{CrAl}}_{3}{\mathrm{O}}_{9}$ forms with a quasi-one-dimensional structure characterized by linear chains of edge-sharing, Cr-and Al-centered, distorted octahedra. The UV/Vis spectrum of high-quality single crystals is marked by broad absorption edges corresponding to direct transitions across a 1.36-eV insulating gap. Measurements of dc magnetic susceptibility $\ensuremath{\chi}$ reveal a fluctuating moment of $2.60\ifmmode\pm\else\textpm\fi{}0.01\phantom{\rule{4pt}{0ex}}{\ensuremath{\mu}}_{B}/\mathrm{Cr}$---reduced from the $3.87\phantom{\rule{0.28em}{0ex}}{\ensuremath{\mu}}_{B}/\mathrm{Cr}$ expected for ${\mathrm{Cr}}^{3+}$, while the Weiss temperature ${\mathrm{\ensuremath{\Theta}}}_{W}=\ensuremath{-}21\ifmmode\pm\else\textpm\fi{}1$ K implies that the prevailing local moment interactions are weakly antiferromagnetic in nature. Some 10% of the fluctuating moment is quenched, presumably due to the onset of an antiferromagnetic or spin glass phase at temperature ${T}^{★}=98\ifmmode\pm\else\textpm\fi{}3$ K, while measurements of magnetization versus field $H$ at $T\ensuremath{\le}10$ K scale as $H/{T}^{0.68(4)}$, suggesting the presence of quantum fluctuations associated with a disordered phase. Density functional theory calculations carried out within the generalized gradient approximation are in excellent agreement with experimental results, asserting that short-range magnetic interactions remnant above ${T}^{★}$ stabilize the insulating state.

Novel universality class for the ferromagnetic transition in the low carrier concentration systems UTeS and USeS exhibiting large negative magnetoresistance

We report the novel critical behavior of magnetization in low carrier concentration systems UTeS and USeS that exhibit the large negative magnetoresistance around the ferromagnetic transition temperatures T_C ~ 85 and 23 K, respectively. UTeS and USeS crystallize in the same orthorhombic TiNiSi-type crystal structure as those of uranium ferromagnetic superconductors URhGe and UCoGe. We determine the critical exponents, beta for the spontaneous magnetization M_s, gamma for the magnetic susceptibility chi, and delta for the magnetization isotherm at T_C with several methods. The ferromagnetic states in UTeS and USeS have strong uniaxial magnetic anisotropy. However, the critical exponents in the two compounds are different from those in the three-dimensional Ising model with short-range magnetic exchange interactions. Similar sets of the critical exponents have been reported for the uranium ferromagnetic superconductors UGe_2 and URhGe, and uranium intermetallic ferromagnets URhSi, UIr and U(Co_0.98Os_0.02)Al. The universality class of the ferromagnetic transitions in UTeS and USeS may belong to the same one for the uranium compounds. The novel critical phenomenon associated with the ferromagnetic transition is observed not only in the uranium intermetallic ferromagnets with the itinerant 5f electrons but also in the low carrier concentration systems UTeS and USeS with the localized 5f electrons. The large negative magnetoresistance in UTeS and USeS, and the superconductivity in UGe_2 and URhGe share the similarity of their closeness to the ferromagnetism characterized by the novel critical exponents.