Complex Magnetic Interactions Research Articles

Epitaxial strain manipulation of the cluster glass state in LaMnO3 films.

As a new-type magnetic state, the cluster glass state in manganite is arousing considerable attention due to its important theoretical value and extensive application prospects in condensed matter physics and spintronics. Due to the complex magnetic interactions, the cluster glass state is difficult to form and regulate in single films. Studies report a new phenomenon that epitaxial strain can regulate the formation of the cluster glass state in LaMnO3 (LMO) films. Comparing LMO thin films with different thicknesses grown on a (001)-oriented LaAlO3 (LAO) single crystal substrate, we found that the 20-nm-thick LMO film is more likely to form the cluster glass state than the 60-nm-thick and 120-nm-thick films. This can be attributed to the uneven distribution of strain and Mn ions in the depth profile. Our work demonstrates that thickness is an important method for regulating the formation of the cluster glass state in LMO films.

3D-Ising-type magnetic interactions stabilized by the extremely large uniaxial magnetocrystalline anisotropy in layered ferromagnetic Cr2Te3

We investigate the magnetocrystalline anisotropy, critical behavior, and magnetocaloric effect in ferromagnetic-layered Cr2Te3. We have studied the critical behavior around the Curie temperature (TC) using various techniques, including the modified Arrott plot (MAP), the Kouvel-Fisher method (KF), and critical isothermal analysis (CI). The derived critical exponents β = 0.353(4) and γ = 1.213(5) fall in between the three-dimensional (3D) Ising and 3D Heisenberg type models, suggesting complex magnetic interactions by not falling into any single universality class. On the other hand, the renormalization group theory, employing the experimentally obtained critical exponents, suggests 3D-Ising-type magnetic interactions decaying with distance as J(r) = r−4.89. We also observe an extremely large uniaxial magnetocrystalline anisotropy energy (MAE) of Ku = 2065 kJ/m3, the highest ever found in any CrxTey based systems, originating from the noncollinear ferromagnetic ground state as predicted from the first-principles calculations. The self-consistent renormalization theory (SCR) suggests Cr2Te3 to be an out-of-plane itinerant ferromagnet. Further, a maximum entropy change of -ΔSMmax≈ 2.08 J/kg − K is estimated around TC for the fields applied parallel to the c-axis.

Three-dimensional critical behavior in Mn1.5Cr1.5O4: A material for magnetocaloric energy conversion

The multifunctional and tunable properties of spinel oxides bring their applicability in various sustainable applications. In this line, the current work systematically examines the magnetic and magnetocaloric properties of Mn1.5Cr1.5O4. The presence of Mn2+ ions in the tetragonal site leads to complex magnetic interactions. It undergoes a ferrimagnetic to paramagnetic transition at 58 K. The critical exponents obtained from the modified Arrot plot, β = 0.346 and γ = 1.051, suggests that the system does not fall into any of the universal class. The exchange interaction strength reveals the coexistence of short- and long-range ordering. Mn1.5Cr1.5O4 displays a magnetic entropy change of -4.11 J kg−1K−1 and a relative cooling power of 70.68 J kg−1 at 58 K for a field change of 70 kOe. Thus, the major results of the study recommend the applicability of Mn1.5Cr1.5O4 towards gas (fuel, H2) liquefaction based on solid-state active magnetic refrigeration technology.

Edge dislocation with [001] [formula omitted] induced positive magnetoresistance in BaTiO3/La0.66Sr0.33MnO3 heterostructure

The magnetoresistance (MR) effect holds immense potential for applications in various fields, including but not limited to storage and sensing. Manganese oxide has garnered significant attention due to its colossal magnetoresistance characteristics. Investigating the effects of the complex magnetic interactions on the magnetism and transport enables a better understanding of magnetic materials. La0.66Sr0.33MnO3 (LSMO) manganese oxides typically exhibiting negative MR as a result of magnetic field-induced spin order, while positive MR typically occurs in systems with spin-orbit coupling (SOC) or P-N junctions. In this work, the magnetic and transport properties of BaTiO3 (BTO)/LSMO heterostructure were studied. By introducing edge dislocation with [001] b→ (burgers vector) in BTO, the c-axis lattice constant is increased, resulting in positive MR in LSMO, which could be modulated by the magnetic field history and the annealing temperature. The nonlinear magnetic order induced by antiferromagnetism at the interface is proposed to cause the positive MR. Finally, the influence of ferroelectric layer on MR could be controlled by the ferroelectric BTO film. The increase in the large lattice constant and the observed variations in MR under magnetic field and annealing temperature provide valuable insights for further studies on the complex oxide.

Complex magnetic interactions and critical behavior analysis in quaternary CoFeV0.8Mn0.2Si Heusler alloy

We investigate the magnetic behavior and critical exponents of quaternary CoFeV0.8Mn0.2Si Heusler alloy to understand the interactions across the Curie temperature (TC). The Rietveld refinement of the x-ray diffraction pattern with the space group F4¯3m confirms a single-phase cubic Y-type crystal structure. The magnetic susceptibility χ(T) data show a ferromagnetic nature with a second-order phase transition from paramagnetic to ferromagnetic at 446±1 K. The saturation magnetization at 5 K is found to be 2.2 μB/f.u., which is close to the Slater–Pauling rule and indicates its half-metallic nature. The values of asymptotic critical exponents (β, γ, and δ) and the TC are extracted through detailed analytical analysis including the modified Arrott plot, the Kouvel–Fisher (K–F) method, and the Widom scaling relation. Interestingly, the estimated values of β=0.369 and γ=1.445 closely approximate the theoretical values of the 3D Heisenberg model across the TC and validate the second-order thermodynamic phase transition. The obtained exponents lead to the collapse of renormalized isotherms, represented by the relationship between the magnetization (m) and the applied magnetic field (h), into two distinct branches above and below the TC, which validates the reliability of the analysis. Furthermore, these exponents suggest that the spin interaction follows a decay pattern of J(r)∼r−4.99, indicating a short-range magnetic ordering, akin to the itinerant-electron 3D Heisenberg model.

Alloying effect of rare-earth tritellurides on the charge density wave and magnetic properties

Among many van der Waals materials rare-earth tritellurides (RTe3) allow studying several phenomena like magnetic, superconducting, and charge density wave (CDW). These studies show the effect of cationic alloying of antiferromagnetic RTe3 for fully tunable near room-temperature CDW properties. DyxGd1−xTe3 and DyxTb1−xTe3 alloys were synthesized through a chemical vapor transport technique, and the rare-earth element composition was controlled by changing the ratio of rare-earth metal reagents. The results show that the lattice parameters can be continuously tuned with the composition of the rare-earth cations leading to the variation of the internal chemical pressure. Temperature-dependent Raman spectroscopy and electric transport measurement show that the CDW transition temperature (TCDW) of RTe3 alloys varies with lattice parameters/chemical pressure spanning across 300–380 K. Additional magnetism studies offer the first insights into the magnetic ordering in RTe3 alloys. The emergence of multiple magnetic transitions implies complex magnetic interactions that arise from interactions between different rare-earth elements. Overall findings introduce ways to control the CDW behavior and provide valuable insights into the magnetic ordering in RTe3 alloys, contributing to further investigation and a better understanding of their properties.

A Comprehensive Review of Ferromagnetic Liquid Dynamics and Nonlinear Thermal Buoyancy Effects

Ferromagnetic liquid is a unique class of fluids that exhibits strong magnetic properties when subjected to a magnetic field. This liquid has been extensively studied in various industrial and scientific applications due to its unique properties such as high thermal conductivity, heat capacity, and electrical conductivity. One of the key phenomena associated with this type of liquid is its nonlinear thermal buoyancy effect, which refers to the motion of the liquid due to variation in temperature caused by a non-uniform magnetic field. In recent years, there has been a growing interest in studying the nonlinear thermal buoyancy effect in ferromagnetic liquids, specifically in the context of heat transport processes.
 Non-Fourier heat flux is another crucial aspect of ferromagnetic liquids that has gained considerable attention among researchers. Non-Fourier heat flux is characterized by the deviation from the linear Fourier's law of heat conduction, where the rate of heat transfer is not proportional to the temperature gradient. In ferromagnetic liquids, this phenomenon is mainly attributed to the presence of magnetic fields, which influence the heat transfer processes within the liquid. This nonlinear heat flux behavior has significant implications in a wide range of applications, including heat dissipation, cooling, and thermal insulation.
 Radiated elastic surfaces are another key feature of ferromagnetic liquids that has recently emerged as a promising area of research. These surfaces are formed when a magnetic field is applied to a ferromagnetic liquid, resulting in the formation of elastic waves on the surface. These waves are created due to the interaction between the magnetic field and the elastic properties of the liquid. The formation of these surfaces has been observed to have a considerable impact on the heat transfer behavior of the liquid, where they act as efficient heat dissipators and significantly enhance the rate of heat exchange between the liquid and its surroundings.
 In summary, the interplay of nonlinear thermal buoyancy, non-Fourier heat flux, and radiated elastic surfaces in ferromagnetic liquids has attracted significant attention in recent years due to its potential for a wide range of practical applications. The understanding of these phenomena has the potential to significantly improve the design and efficiency of various heat transfer processes, making ferromagnetic liquids an important area of study in materials science and engineering. Future research in this field is expected to focus on developing more comprehensive models and experimental techniques to further explore the complex thermal and magnetic interactions in ferromagnetic liquids.

Crystal structure and magnetic properties of Gd8Mn3Sb19

In this study, a novel magnetic semimetal compound, Gd8Mn3Sb19, was synthesized successfully via high-temperature solid-state reaction. The crystal structure of Gd8Mn3Sb19 was determined using both single crystal and powder X-ray diffraction techniques, revealing a non-centrosymmetric orthorhombic space group, Pmn21 (No. 31). The Sb atoms in Gd8Mn3Sb19 form five-atom-wide Sb57− ribbons, narrower three-atom-wide Sb35− ribbons, and single Sb3− anions. On the other hand, both Gd3+ and Mn2+ ions form the distorted Gd3 and Mn3 triangular lattices, respectively. The magnetic measurements suggest the complex magnetic interactions contributed by both Gd3+ and Mn2+ ions. A sharp peak observed in the magnetic susceptibility plot at approximately 25 K corresponds to the antiferromagnetic-type transition in Gd8Mn3Sb19. Furthermore, the magnetic measurements along different directions indicate the strong magnetic anisotropy present in Gd8Mn3Sb19, which is likely due to the complex magnetic interactions arising from the existence of Gd and Mn ions. Finally, the electrical resistivity measurements of Gd8Mn3Sb19 indicate semimetallic behavior with a positive magnetoresistance.

Investigation of Charge-Ordered Barium Iron Fluorides with One-Dimensional Structural Diversity and Complex Magnetic Interactions.

Three mixed-valence barium iron fluorides, Ba7Fe7F34, Ba2Fe2F9, and BaFe2F7, were prepared through hydrothermal redox reactions. The characteristic structures of these compounds feature diverse distributions of FeIIF6 octahedra and FeIIIF6 groups. Ba7Fe7F34 contained one-dimensional infinite ∞[FeIIFeIII6F34]14- double chains, comprising cis corner-sharing octahedra along the b direction; Ba2Fe2F9 contained one-dimensional ∞[Fe2F9]4- double chains, consisting of cis corner-sharing octahedra along the chain (a-axis direction) and trans corner-sharing octahedra vertical to the chain, while BaFe2F7 revealed three-dimensional (3D) frameworks that consist of isolated edge-sharing dinuclear FeII2F10 units linked via corners by FeIIIF6 octahedra. Magnetization and Mössbauer spectroscopy measurements revealed that Ba7Fe7F34 exhibits an antiferromagnetic phase transition at ∼11 K, where ferrimagnetic ∞[FeIIFeIII6F34]14- double chains are arranged in a paralleling manner, while Ba2Fe2F9 shows canted antiferromagnetic ordering at ∼32.5 K, leading to noncollinear spin ordering.

Semiconductor to half-metal transition in magnetic Ce cation incorporated A-site-ordered quadruple perovskite CeMn3Mn4O12

The charge degree of freedom of A-site cation as well as B-site cation plays a significant role in determining the internal charge distribution and gives rise to fascinating physical properties in perovskite oxides. Here, we discuss the magnetic couplings and electronic structures of rare-earth Ce cation incorporated A-site-ordered quadruple perovskite CeMn3Mn4O12 via first-principles calculations. This report demonstrates that the A site Ce is magnetic cation with quantity of 4 f electrons, which is quite different from the nonmagnetic Ce4+ usually found in isostructural compounds. As a result, not only the A′ and B site manganese sublattices but also the A site cerium sublattice is involved in the complex magnetic interactions. In the low-temperature phase, CeMn3Mn4O12 is ferrimagnetic with the Ce(↓)-Mn1(↑)-Mn2(↓)-Mn3(↑)-Mn4(↑)-Mn5(↓) type, in which the effective magnetic couplings are generated from A-site Ce sublattice as well as the antiparallel arrangement within both the A and B site manganese sublattices. The analysis of electronic structure reveals the valence distribution is Ce3+Mn3+3Mn3+4O2-12 where both the oxidation state of Ce and Mn is +3. Nevertheless, ferromagnet is the most favorable in energy with a large saturated magnetic moment at the high-temperature phase. Interestingly, the electronic structure undergoes a semiconducting to half-metallic transition accompanying with the phase transformation. The present results offer a new strategy to realizing the tunable charge distribution via variable valence A site cation in A-site-ordered quadruple perovskites and thus open an avenue to modulate these materials with exotic properties.

Unraveling the role of Sm 4f electrons in the magnetism of SmFeO3

Magnetic rare-earth orthoferrite perovskites ($R$FeO${}_{3})$ host a variety of functional properties particularly suitable for next-generation, ultrafast spintronic devices. A key ingredient is the complex magnetic interaction at play between the two magnetic substructures. SmFeO${}_{3}$ has attracted particular interest because of its high-temperature spin reorientation transition and anomalous temperature-dependent lattice vibrational modes. Through first-principles calculations, the authors unveil here the interplay of the Sm-Fe exchange with the strong Sm $f$ anisotropy as the dominant microscopic mechanism, and the nature of the anomalous vibrations.

Magnetic and electrical properties of a heavy-fermion compound EuRh2Al8

We report the magnetic, thermodynamic, and electrical properties of ${\mathrm{EuRh}}_{2}{\mathrm{Al}}_{8}$, a Eu-based heavy fermion member in the ${\mathrm{RT}}_{2}{\mathrm{X}}_{8}$ families with an orthorhombic $Pbam$ structure. Magnetization studies reveal multiple phase transitions in the single crystals, including two successive antiferromagnetic transitions at ${T}_{N1}\ensuremath{\sim}12.5\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ and ${T}_{N2}\ensuremath{\sim}8.2\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. These two transitions are closely related to competing magnetic interactions in the Shastry-Sutherland lattice, which further give rise to another in-plane spin-flop transition at 1/3 of the full magnetization below 5 K when the applied magnetic field is higher than 6 T within the $ab$ plane. In addition to these, specific heat measurements in ${\mathrm{EuRh}}_{2}{\mathrm{Al}}_{8}$ demonstrate a heavy fermion state with a large Sommerfeld coefficient $\ensuremath{\gamma}=393\phantom{\rule{0.16em}{0ex}}\mathrm{mJ}\ifmmode\cdot\else\textperiodcentered\fi{}{\mathrm{mol}}^{\ensuremath{-}1}\ifmmode\cdot\else\textperiodcentered\fi{}{\mathrm{K}}^{\ensuremath{-}2}$. Electrical transport measurement shows that its resistivity exhibits a ${T}^{2}$-dependence below ${T}_{N2}$ and a robust linear $T$-dependence above ${T}_{N1}$, which is also typical of a heavy fermion metal. Our work provides fundamental physical properties of ${\mathrm{EuRh}}_{2}{\mathrm{Al}}_{8}$ and promotes understanding of the complex magnetic interactions and unusual spin correlations in the ${\mathrm{RT}}_{2}{\mathrm{X}}_{8}$ families.

Topological spin textures in 1T -phase Janus magnets: Interplay between Dzyaloshinskii-Moriya interaction, magnetic frustration, and isotropic higher-order interactions

The search for topological magnetism in two-dimensional (2D) magnetic materials is one of the hot topics in spintronics. We present comprehensive studies of magnetic phases in a series of Janus monolayers $\mathrm{Mn}XZ$ (MnAsBr, MnAsI, MnPBr, and MnPCl) and $\mathrm{Cr}YZ$ ($Y=\mathrm{Se}$, Te; and $Z=\mathrm{Cl}$, Br, I) via combining first-principles calculations and atomistic spin model simulations. Sizable Dzyaloshinskii-Moriya interaction can be realized in the $\mathrm{Mn}XZ$ and $\mathrm{Cr}YZ$ monolayers due to their intrinsic inversion symmetry breaking. More interestingly, the $\mathrm{Mn}XZ$ and $\mathrm{Cr}YZ$ monolayers exhibit different degrees of magnetic frustration and isotropic higher-order interactions. Lastly, our atomistic spin model simulations demonstrate that a variety of topological spin textures can be generated by the interplay among complex magnetic interactions. These results provide valuable information and fundamental understanding for topological magnetism in 2D magnets.

Strange Metallicity and Magnetic Order in the CoNi(Cr/V) Medium-Entropy Alloy System.

CoNiCr is a prototypical example of topical multi-principle element alloys with superior cryogenic and high-temperature mechanical strength, corrosion, oxidation resistance, and yet-to-be-explored magnetic and electronic functionalities. The remarkable properties of this transition metal ternary system are not only due to atomic radii, electronic configurational mismatch, and atomic volume misfit but are also dependent on the debated magnetically driven chemical short-range order. The current study focuses on the electric and magnetic properties of the single-phase face-centered cubic CoNi(Cr/V) system in which V is introduced to the system at the expense of Cr to fine-tune the volume misfit in the system. All the samples exhibited ultra-small magnetic moments due to the complex magnetic interactions of the constituent elements. The electric transport measurements revealed a strange metallicity evidenced through the observation of the linear temperature dependence of the resistivity. Our findings support the recent theoretical studies on the magnetically driven chemical short-range order of the CoNiCr system.

Magnetic behaviors and magnetocaloric effects in rare earth high-entropy amorphous/nanocrystalline alloys

Rare earth high-entropy alloys (RE–HEAs) exhibit great potential to be applied as refrigerants due to their good comprehensive magnetocaloric properties. In this work, octary GdTbDyHoErTmCoAl and GdTbDyHoErTmCoNi RE–HEAs with amorphous/nanocrystalline structure exhibiting comparable magnetocaloric effect were synthesized. Both RE–HEAs show a second-order magnetic phase transition in the temperature range of hydrogen liquefaction. Due to the complex magnetic interactions, a spin glass-like behavior at low temperatures is observed in the RE–HEAs. A superior magnetocaloric effect is obtained in the nanocrystalline GdTbDyHoErTmCoNi high-entropy alloy that is multiphase attributed to a stronger magnetic exchange interaction when compared with the other that exhibits single amorphous structure. Despite heterogeneous microstructure, homogeneous chemical distributions are observed in the partially crystallized high-entropy alloy. In addition, the magnetocaloric effect and magnetic transition behavior of rare earth medium- and high-entropy alloys, including the RE–HEAs in this study, are summarized and discussed. The results in this work provide a helpful guide for the design of RE–HEAs for hydrogen liquefaction applications with excellent magnetocaloric effects.

Thermodynamic insights into the intricate magnetic phase diagram of EuAl4

The tetragonal intermetallic compound EuAl$_{4}$ hosts an exciting variety of low temperature phases. In addition to a charge density wave below 140 K, four ordered magnetic phases are observed below 15.4 K. Recently, a skyrmion phase was proposed based on Hall effect measurements under a $c$-axis magnetic field. We present a detailed investigation of the phase transitions in EuAl$_{4}$ under $c$-axis magnetic field. Our dilatometry, heat capacity, DC magnetometry, AC magnetic susceptibility, and resonant ultrasound spectroscopy measurements reveal three magnetic phase transitions not previously reported. We discuss what our results reveal about the character of the magnetic phases. Our first key result is a detailed $H \parallel [001]$ magnetic phase diagram mapping the seven phases we observe. Second, we identify a new high-field phase, phase VII, which directly corresponds to the region were skyrmions have been suggested. Our results provide guidance for future studies exploring the complex magnetic interactions and spin structures in EuAl$_{4}$.

Electronic reconstruction induced inverted hysteresis loop in La0.67Sr0.33MnO3/Pb(Zr0.52Ti0.48)O3 superlattices

The multiferroic heterointerfaces, based on perovskite transition metal oxides, have been established as the effective way to build an interface with emergent phenomena owing to the coexistence and competition of complex interaction at the interface. Here, the La0.67Sr0.33MnO3/Pb(Zr0.52Ti0.48)O3 (LSMO/PZT) multiferroic superlattices (SLs) grown on (001)-, (110)-, and (111)-oriented SrTiO3 substrates have been systematically investigated. An inverted hysteresis loop (IHL) with a negative coercivity and remanence was found in the (001)- and (111)-oriented SLs, while was absent in (110)-oriented SLs. Detailed magnetic measurements demonstrate the contribution of both scanning field and temperature to the IHL, and the positive exchange bias in the minor hysteresis loops indicates the antiferromagnetic coupling between the interface and the bulk. The polarity discontinuity at the (001)- and (111)-oriented LSMO/PZT interface leads to the charge redistribution and is responsible for the unexpected IHL phenomenon. Our study highlights the significance of the electronic reconstruction due to the polarity discontinuity at the interface and provides a new approach to deal with complex magnetic interactions at the interface.

Investigating the A n+1B n X3n+1 Homologous Series: A New Platform for Studying Magnetic Praseodymium Based Intermetallics.

The recent discovery of the An+1BnX3n+1 (A = lanthanide, B = transition metal, X = tetrel) homologous series provides a new platform to study the structure–property relationships of highly correlated electron systems. Several members of Cen+1ConGe3n+1 (n = 1, 4, 5, 6, and ∞) show evidence of heavy electron behavior with complex magnetic interactions. While the Ce analogues have been investigated, only n = 1, 2, and ∞ of Prn+1ConGe3n+1 have been synthesized, with n = 1 and 2 showing a nonsinglet magnetic ground state. The Pr analogues can provide a platform for direct comparison of highly correlated behavior. In this perspective, we discuss the impetus for synthesizing the Prn+1ConGe3n+1 members and present the structural characterization of the n = 3 and n = 4 members. We lay the foundation for future investigations of the Prn+1ConGe3n+1 family of compounds and highlight the importance of complementary methods to characterize new quantum materials.

Polaronic Conductivity in Cr2Ge2Te6 Single Crystals

AbstractIntrinsic 2D ferromagnetic semiconductors are an important class of materials for spin‐charge conversion applications. Cr2Ge2Te6 retains long‐range magnetic order in the bilayer at cryogenic temperatures and shows complex magnetic interactions with considerable magnetic anisotropy. Here, a series of structural, magnetic, X‐ray scattering, electronic, thermal transport and first‐principles calculation studies are performed, which reveal that localized electronic charge carriers in Cr2Ge2Te6 are dressed by the surrounding lattice and are involved in polaronic transport via hopping that is observed via magnetocrystalline anisotropy. This opens the possibility for manipulation of charge transport in Cr2Ge2Te6—based devices by electron–phonon‐ and spin–orbit coupling‐based tailoring of polaron properties.

Assembling Diverse Skyrmionic Phases in Fe3 GeTe2 Monolayers.

Skyrmionic magnetic states are promising in advanced spintronics. This topic is experiencing recent progress in 2D magnets, with, for example, a near 300 K Curie temperature observed in Fe3 GeTe2 . However, despite previous studies reporting skyrmions in Fe3 GeTe2 , such a system remains elusive, since it has been reported to host either Néel-type or Bloch-type textures, while a net Dzyaloshinskii-Moriya interaction (DMI) cannot occur in this compound for symmetry reasons. It is thus desirable to develop an accurate model to deeply understand Fe3 GeTe2 . Here, a newly developed method adopting spin invariants is applied to build a first-principle-based Hamiltonian, which predicts colorful topological defects assembled from the unit of Bloch lines, and reveals the critical role of specific forms of fourth-order interactions in Fe3 GeTe2 . Rather than the DMI, it is the multiple fourth-order interactions, with symmetry and spin-orbit couplings considered, that stabilize both Néel-type and Bloch-type skyrmions, as well as antiskyrmions, without any preference for clockwise versus counterclockwise spin rotation. This study also demonstrates that spin invariants can be used as a general approach to study complex magnetic interactions.