Magnetic Transition Research Articles

Disclosing the magnetic ground state of PrBaMn2O6

In this work, we report a neutron diffraction study on a single crystal of the layered PrBaMn2O6 perovskite. This compound undergoes two consecutive magnetic transitions with decreasing temperature. At TC ≈ 309 K, a long-range ferromagnetic ordering is established with the Mn magnetic moments oriented along the c axis. Below TN ≈ 240 K, a spin reorientation gives rise to a sudden decrease of the magnetization and the formation of an antiferromagnetic order. This magnetic transition is also accompanied by an electronic localization caused by a structural phase transition from a high-temperature tetragonal phase (P4/mmm) into a low-temperature orthorhombic one (P21am). Our neutron diffraction study at 12 K has unambiguously identified that the ground magnetic structure for this compound is a layered antiferromagnetic structure along the c axis with the Mn moments oriented in the ab plane along one diagonal of the primitive tetragonal cell. No sign of magnetic scattering associated to a CE-type magnetic structure was found in our study, discarding its occurrence in this compound. This result excludes the occurrence of a charge order transition to account for the electronic localization and it is fully consistent with previous structural studies showing a unique crystallographic site for Mn atom in the low-temperature phase. A symmetry analysis was carried out to identify the magnetic space group of the ferromagnetic order above TN and the two possible groups for the antiferromagnetic ordering below TN.

B-site ordered and disordered phases in A-site columnar-ordered quadruple perovskites Nd2MnMn(Mn4−xSbx)O12

Solid solutions Nd2MnMn(Mn4−xSbx)O12, belonging to the A-site columnar-ordered quadruple perovskite subfamily A2A′A′′B4O12 and prepared by a high-pressure, high-temperature method at about 6 GPa and about 1700 K, were investigated in a compositional range of 0.2 ≤ x ≤ 2.0. Crystal structures were studied using synchrotron powder X-ray diffraction. Two regions with different cation orders in the B sublattice were found: a narrow region of 0.8 ≤ x ≤ 1.0 had a B-site disordered structure with space group P42/nmc (No. 137), and a wider region of 1.6 ≤ x ≤ 2.0 had a B-site rock-salt-ordered structure with space group P42/n (No. 86). Small anti-site disorder of Nd and Mn was detected among the A, A′, and A′′ sites. In the B-site rock-salt-ordered structures, one B site was solely occupied by Mn, the second B′ site had a mixture of Sb and Mn (for x < 2). The samples showed complex magnetic behavior with two ferrimagnetic transitions. TC1 monotonically increased (from 66 K to 75 K) and TC2 was almost constant (about 6–7 K) for 0.8 ≤ x ≤ 1.0. TC1 monotonically decreased (from 77 K to 63 K) and TC2 monotonically increased (from 19 K to 39 K) for 1.6 ≤ x ≤ 2.0. There was evidence for the third magnetic transition in the 1.7 ≤ x ≤ 2.0 samples, and TC3 increased from 13 K to 20 K with increasing x.

Giant magnetocaloric effect of Ni-Co-Mn-Ti all-d Heusler alloys in high magnetic fields

Ni-Co-Mn-Ti all-d Heusler alloys are attracting considerable attention for solid-state caloric-cooling applications due to their promising combination of excellent caloric and mechanical properties. Here, we report on the maximum attainable magnetocaloric effect in Ni37Co13Mn34.5Ti15.5, which shows a first-order magnetostructural martensitic transformation around room temperature. Heat capacity measurements reveal a giant transition entropy change of 43.5J(kgK)\\protect \\relax \\special {t4ht=−}1 and are utilized to estimate the magnetocaloric effect as well as the magnetic fields required to saturate it in isothermal and adiabatic conditions. Confirming the results based on this approach, we achieve maximum isothermal entropy changes and directly measured adiabatic temperature changes of 37.8J(kgK)\\protect \\relax \\special {t4ht=−}1 and -20.2K, respectively. Thus, the herein reported maximum attainable magnetocaloric effect outperforms classical Ni-Mn-based Heusler alloys, such as Ni(-Co)-Mn-In. Especially the saturated adiabatic temperature change surpasses all previously published values of magnetic field-induced first-order phase transitions measured around room temperature in pulsed magnetic fields in recent years. Thereby, we demonstrate that Ni(-Co)-Mn-Ti Heusler alloys are particularly suitable for the application of sufficiently large external stimuli to fully induce the phase transition and exploit their intrinsically large caloric effect.

Influence of synthesis protocol on structure, magnetic and magnetocaloric properties of ErCrO3

In this study, we investigated the morphology, structure, magnetic, and magnetocaloric properties of ErCrO3 (ECO) nanoparticles synthesized through two distinct chemical routes: combustion and hydrothermal methods. X-ray diffraction analysis revealed a well-crystallized orthorhombic pbnm phase in both samples. The broader Raman peaks observed in the hydrothermal sample indicate a larger strain of 0.138%, compared to the combustion-derived sample. A significant reduction in the magnetic phase transition temperature was observed for ECO nanoparticles synthesized via the hydrothermal method (117 K) compared to those derived from combustion (∼130 K), which can be attributed to size-induced strain. The hydrothermal ECO samples exhibited a broader temperature span and lower entropy changes compared to the combustion-derived counterparts. Consequently, we observed an improved relative cooling power of 523 J K−1 and entropy change of −10.8 J kg−1 K−1 at a magnetic field of 50 kOe. These findings are promising for magnetic refrigeration applications. The ability to tailor magnetocaloric properties through straightforward synthesis methods underscores their significance in advancing potential applications.

Supramolecular Spin Chains via Radical-Radical Contacts Stabilizing Ferromagnetic Interactions Between Heisenberg or Ising-Like Spins.

A new paramagnetic ligand, 4-(2'-4-(2''-furyl)-pyrimidyl)-1,2,3,5-dithiadiazolyl (furylpymDTDA) and three transition metal coordination complexes, M(hfac)2(furylpymDTDA) M=Mn, Co, Ni; hfac=1,1,1,5,5,5-hexafluoroacetylacetonato-), are reported. The solid-state structures are influenced by the geometry of the coordination sphere of the M(II) centers: trigonal (Mn) vs. octahedral (Co and Ni). While the hs-Mn(II) complex exhibits pairwise multi-centre 2-electron bonds (i. e., pancake bonds) between the planar π radical DTDA moieties, the hs-Co(II) and Ni(II) complexes crystallize with close contacts between coordinated furylpymDTDA radical ligands that define linear 1D arrays of molecular units. The magnetic data for the hs-Co(II) and Ni(II) complexes indicate ferromagnetic (FM) interactions between molecular units, apparently mediated by radical-radical contacts along the supramolecular chains. Computational analysis suggests proximity between regions of large α- and β-spin density on neighbouring molecular sites enabling FM exchange, in accordance with the McConnell I mechanism. The magnetic data for the Ni(II) complex are consistent with a Heisenberg spin chain, whereas the hs-Co(II) complex exhibits Ising-like spin chain behaviour and a magnetic phase transition to an FM ordered state at 4.6 K.

Modulation method of studying two-phase antiferromagnetic domain structures created by a pulsed magnetic field

It is shown that studies of the coercivity of AFM domain walls that arise in antiferromagnets during the first-order spin-orientation transition can be used as a tool for detecting, identifying, and studying spin structures realized in a crystal under the influence of an external magnetic field. The use of high-frequency modulation of the magnetic field made it possible to expand the capabilities of the standard induction method of studying magnetic phase transitions in antiferromagnets. The proposed measurement method was tested on well-known MnF2 and Cr2O3 crystals.

Silicon nitride directional coupler-based polarization beam splitter utilizing shallow ridge waveguides for improved fabrication tolerance

This study presents the design and fabrication of a silicon nitride (Si3N4) asymmetrical directional coupler (DC)-based polarization beam splitter (PBS) utilizing a shallow ridge waveguide structure. The use of Si3N4 with a moderate refractive index contrast and the design of a shallow ridge waveguide enables the DC structure to have a wider coupling gap of approximately 600 nm, which can be readily achieved with standard I-line lithography. The simulation results indicate that the polarization splitting is highly efficient with minimal insertion loss. This is corroborated by the experimental measurements, which show consistent broadband performance. The fabricated polarization beam splitter (PBS) exhibits a high polarization extinction ratio (PER) of over 20 dB for both transverse electric (TE) and transverse magnetic (TM) modes across a broad bandwidth of 120 nm (1500-1620 nm). This work demonstrates the potential of shallow ridge Si3N4 waveguides to enhance the fabrication tolerance and performance of integrated photonic devices.

Changing magnetic ground state by an electric field in a single-layer FeCl2

Abstract Employing the electric field has been performed to investigate the magnetic ground state in a single-layer iron dichloride (FeCl2). We provided some lattice parameters to see the ground state dependency on the electric field. To minimize the computational time, we applied the generalized Bloch theorem via density functional theory to avoid the supercell approach. As we varied the electric field, we saw the magnetic transition for some lattice parameters. In addition, the magnetic moments were nearly stable for all those states, indicating the high spin state. As a concluding remark, employing the electric field is very useful to manipulate the ground state that can be applied to magnetism-based nanotechnology.

Large coercivity and enhanced magnetization in La-substituted Sm6Mn23 alloys

The magnetic properties of Sm6Mn23-based alloys are still not fully understood for their high complexity in magnetic and crystallographic structures. This work presents studies of the structure and magnetic properties of Sm6Mn23 and Sm5LaMn23 alloys. The results show that both the binary and La-substituted ternary alloys crystallize in a cubic Th6Mn23 type structure (Fm-3m) with trace amount of Mn impurities. The lattice parameter of Sm5LaMn23 is slightly larger than that of Sm6Mn23. The Curie temperature of Sm5LaMn23 is ∼403 K, which is lower than that of Sm6Mn23. A field-dependent magnetic transition was observed in Sm5LaMn23, which shows a decreasing temperature at which Sm5LaMn23 exhibiting maximal magnetization with increasing field, indicating a suppression of the antiferromagnetic coupling of the rare earth and Mn moments under applied field. Large coercivities up to 0.74 T and 1.2 T are observed in Sm5LaMn23 bulk alloys and powders, respectively. The saturate magnetization, the remanent magnetization, and the coercivity of Sm5LaMn23 at 5 K are much higher than that of Sm6Mn23. The ball-milled Sm5LaMn23 powders exhibit significantly enhanced coercivity and magnetization. The refinement of the grain size during ball-milling results in the enhanced coercivity. The magnetic purification of the powders and possible local ferromagnetic configuration of the surface Mn atoms may result in the enhanced magnetization.

Unraveling the electronic structure and magnetic transition evolution across monolayer, bilayer, and multilayer ferromagnetic Fe3GeTe2

Two-dimensional (2D) van der Waals (vdW) magnets have sparked widespread attention due to their potential in spintronic applications as well as in fundamental physics. Ferromagnetic vdW compound Fe3GeTe2 (FGT) and its Ga variants have garnered significant interest due to their itinerant magnetism, correlated states, and high magnetic transition temperature. Experimental studies have demonstrated the tunability of FGT’s Curie temperature, TC, through adjustments in quintuple layer numbers (QL) and carrier concentrations, n. However, the underlying mechanism remains elusive. In this study, we employ molecular beam epitaxy (MBE) to synthesize 2D FGT films down to 1 QL with precise layer control, facilitating an exploration of the band structure and the evolution of itinerant carrier density. Angle-resolved photoemission spectroscopy (ARPES) reveals significant band structure changes at the ultra-thin limit, while first-principles calculations elucidate the band evolution from 1 QL to bulk, largely governed by interlayer coupling. Additionally, we find that n is intrinsically linked to the number of QL and temperature, with a critical value triggering the magnetic phase transition. Our findings underscore the pivotal role of band structure and itinerant electrons in governing magnetic phase transitions in such 2D vdW magnetic materials.

Structural, Magnetic, and Magneto-Thermal Properties of Rare Earth Intermetallic GdRhIn.

We study the structural, magnetic, and magneto-thermal properties of the GdRhIn compound. The room-temperature X-ray diffraction measurements show a hexagonal crystal structure. Temperature and field dependence of magnetization suggest two magnetic transitions-antiferromagnetic to ferromagnetic at 16 K and ferromagnetic to paramagnetic at 34 K. The heat capacity measurements confirm both the magnetic transitions in GdRhIn. The magnetization data were used to calculate isothermal magnetic entropy change and refrigerant capacity in GdRhIn, which was found to be 10.3 J/Kg-K for the field change of 70 kOe and 282 J/Kg for the field change of 50 kOe, respectively. The large magnetocaloric effect in GdRhIn suggests that the material could be used for magnetic refrigeration at low temperatures.

Magnetic and topological phase transition in the symmetry-breaking 1T′-FeSe2 monolayer

Magnetic and topological phase transition in the symmetry-breaking 1T′-FeSe2 monolayer

Study of Flow and Zinc Dross Removal in Hot-Dip Galvanizing with Combined Traveling Magnetic Field

The removal of zinc dross, which continuously generates and partially floats on a molten zinc surface, has been a persistent challenge during hot-dip galvanizing. Herein, a three-dimensional mathematical model coupled with the electromagnetic field, flow field and air-knife jet flow was established to investigate the flow and zinc dross removal in a zinc pot. Two types of traveling magnetic field combined modes (Mode 1 and Mode 2) were compared. The surface dross removal efficiency was introduced to evaluate the ability of the zinc flow field to compel the movement of zinc dross. The research findings indicate that, in comparison to the influence of strip steel line speed, both the electromagnetic field and air-knife jet have a more pronounced effect on altering the flow characteristics of a molten zinc at surface. The dross removal efficiency for Mode 1 is much far superior to that of Mode 2. With an increase in the driving current, the dross removal efficiency increases while the excessive driving current cannot promote the dross removal efficiency significantly.

Zero-crosstalk silicon photonic refractive indexsensor with subwavelength gratings.

Silicon photonic index sensors have received significant attention for label-free bio and gas-sensing applications, offering cost-effective and scalable solutions. Here, we introduce an ultra-compact silicon photonic refractive index sensor that leverages zero-crosstalk singularity responses enabled by subwavelength gratings. The subwavelength gratings are precisely engineered to achieve an anisotropic perturbation-led zero-crosstalk, resulting in a single transmission dip singularity in the spectrum that is independent of device length. The sensor is optimized for the transverse magnetic mode operation, where the subwavelength gratings are arranged perpendicular to the propagation direction to support a leaky-like mode and maximize the evanescent field interaction with the analyte space. Experimental results demonstrate a high wavelength sensitivity of - 410nm/RIU and an intensity sensitivity of 395dB/RIU, with a compact device footprint of approximately 82.8μm2. Distinct from other resonant and interferometric sensors, our approach provides an FSR-free single-dip spectral response on a small device footprint, overcoming common challenges faced by traditional sensors, such as signal/phase ambiguity, sensitivity fading, limited detection range, and the necessity for large device footprints. This makes our sensor ideal for simplified intensity interrogation. The proposed sensor holds promise for a range of on-chip refractive index sensing applications, from gas to biochemical detection, representing a significant step towards efficient and miniaturized photonic sensing solutions.

Theoretical investigation of [formula omitted]-type doping modulated interlayer magnetic and potential topological phases transition in MnSb[formula omitted]Te[formula omitted] based systems

MnSb2Te4, as an important member of intrinsic magnetic topological insulator MnBi2Te4 family, shows promise for realizing quantum anomalous Hall effect (QAHE). However, interlayer A-type antiferromagnetic coupling has been a challenge to successfully observe this novel physical phenomenon in MnSb2Te4 system. Based on density functional theory, our calculations demonstrated that doping p-type non-magnetic elements into 2 SLs and 3 SLs of MnSb2Te4 can induce a magnetic phase transition from interlayer antiferromagnetic to ferromagnetic states with a Curie temperature up to 52.2 K. Moreover, our calculations present that interlayer ferromagnetic coupling and band gap in Ca-doped 2 SLs MnSb2Te4 systems can be further tuned by applying compressive strain. In addition, the interlayer ferromagnetic coupling in MnSb2Te4/Sb2Te3/MnSb2Te4 sandwich heterostructure by p-type doping can be enhanced, The detailed electronic structure analysis show that realization of interlayer ferromagnetic coupling is mainly related to a redistribution of d-electron orbital occupancy in Mn atoms of various SL layers. These findings not only advance the understanding of interlayer ferromagnetic order in ultrathin MnSb2Te4 layers, but also provide new way to realize the QAHE in MnSb2Te4 based systems without introducing extraneous magnetic disorder.

Construction of Chiral-Magnetic-Dielectric Trinity Structures with Different Magnetic Systems for Efficient Low-Frequency Microwave Absorption.

The fabrication of carbon nanocoil (CNC)-based chiral-dielectric-magnetic trinity composites holds great significance in low-frequency microwave absorption fields. However, it is not clear that how the different magnetic systems affect the magnetic and frequency responses of the composites. Herein, four types of magnetic metals, FeCo, CoNi, FeNi, and FeCoNi, are selected to be combined with the chiral templates respectively, resulting in four types of chiral-dielectric-magnetic composites with similar morphology. The CNC templates endow all the composites with excellent dielectric loss. Further permeability analysis and the micro-magnetic simulation confirm that the frequency response region can be well adjusted by changing the magnetic systems with specific magnetic resonance modes and magnetic domain motion. Due to the synergistic effect between magnetism, chirality, and dielectricity, the FeNi-based composites exhibit the best low-frequency microwave absorption performance. The minimum RL of -60.7 dB is achieved at 6.7 GHz with an ultra-low filling ratio of 10%, and the EAB value in low-frequency region is extended to 3.7 GHz. This study provides further guidelines for the design of the chiral-dielectric-magnetic trinity composites in low-frequency microwave absorption.

Pressure-induced magnetic and topological transitions in non-centrosymmetric MnIn2Te4

In recent years, the study of magnetic topological materials, with their variety of exotic physics, has significantly flourished. In this work, we predict the interplay of magnetism and topology in the non-centrosymmetric ternary manganese compound MnIn2Te4under external hydrostatic pressure, using first-principles calculations and symmetry analyses. At ambient pressure, the ground state of the system is an antiferromagnetic insulator. With the application of a small hydrostatic pressure (∼0.50 GPa), it undergoes a magnetic transition, and the ferromagnetic state becomes energetically favorable. At ∼2.92 GPa, the ferromagnetic system undergoes a transition into a Weyl semimetallic phase, which hosts multiple Weyl points in the bulk. The presence of non-trivial Weyl points have been verified by Wilson bands computations and the presence of characteristic surface Fermi arcs. Remarkably, we discover that the number of Weyl points in this system can be controlled by pressure and that these manifest in an anomalous Hall conductivity (AHC). In addition to proposing a new candidate magnetic topological material, our work demonstrates that pressure can be an effective way to induce and control topological phases, as well as AHC, in magnetic materials. These properties may allow our proposed material to be used as a novel pressure-controlled Hall switch.

Single crystal growth and magnetic properties in triangular chain compound Ni2SiO4

Sub-centimeter-scale Ni2SiO4 single crystals were grown by a flux method with K2MoO4 as the flux. The obtained crystals exhibit high quality and were characterized using X-ray diffraction, chemical analysis, and magnetic properties, including high magnetic field (H) magnetization (M) measurements. The results of magnetic susceptibility and specific heat of a single crystal reveal significant magnetic anisotropy and antiferromagnetic ordering below TN = 30 K. High-field magnetization up to 43 T of polycrystalline shows six magnetic phase transitions at H1 = 14 T, H2 = 18.4 T, H3 = 23 T, H4 = 29 T, H5 = 32.5 T, and H6 = 37 T, forming a complex magnetic phase diagram with seven phases. Notably, the M exhibits a linear relationship with H during phases V (H4 < H < H5) and VII (H > H6), showing intercepts at 0 and half of magnetization saturation respectively, implying the presence of a spin flop transition and a 1/2 magnetization plateau. These novel phenomena in such a triangular chain system highlight complex physical nature, making Ni2SiO4 a promising candidate for studying intricate magnetic interactions.

Magnetic phase transition and cryogenic magnetocaloric properties in the RE6Ni2.3In0.7 (RE = Ho, Er, and Tm) compounds

Magnetic phase transition and cryogenic magnetocaloric properties in the <i>RE</i>6Ni2.3In0.7 (<i>RE </i>= Ho, Er, and Tm) compounds

Excellent Barocaloric Effect by Modulating Geometrical Frustrations in Mn3Pt.

Barocaloric materials hold great promise for next-generation solid-state cooling devices because of their green and efficient cooling performance. The insights into low-pressure-driven barocaloric materials are expected to pave the way for the widespread application of barocaloric refrigeration technology. Here, we reveal the low-pressure-driven large barocaloric effect (BCE) modulated by geometrical frustrations in Mn3Pt. The highest sensitivity to pressure of Mn3Pt in metal BCE materials results in an excellent temperature-change strength of 9.77 K 100-1 MPa-1. Neutron powder diffraction and first-principles calculations point out the dual effect of geometrical frustration on modulating the unusual BCE, which not only induces giant volume expansion by inspiring strong spin fluctuation and magnetic moment but also enhances the sensitivity of magnetic phase transition. The model of the dual effect of geometrical frustration in magnets with geometrical frustration is established, which will promote the research progress of barocaloric refrigeration devices.