Ferromagnetic Transition Research Articles

First-principle calculations of magnetic properties of Ho6(Fe, Mn)Bi2 compounds

The magnetic properties of Ho6MnBi2 and Ho6FeBi2 crystals are investigated by means of density functional theory. These materials are currently an active subject of research in the context of magnetic refrigeration applications since they exhibit a remarkable magnetocaloric effect. In this work, the equation of state, density of states and magnetic moments are calculated and compared with previous experimental results for these materials. Also, the Curie temperatures for the paramagnetic to ferromagnetic phase transition observed in these systems are calculated from first principles. All the calculated quantities are in reasonable agreement with experimental data, which suggests that density functional theory could provide a reliable framework to theoretically investigate the magnetic properties of intermetallic ternary compounds.Graphical abstract

EELS and 4D-STEM Investigation of Strain Induced Ferromagnetic Transition and Domain Formation at LaFeO3/SrTiO3 Interface

EELS and 4D-STEM Investigation of Strain Induced Ferromagnetic Transition and Domain Formation at LaFeO3/SrTiO3 Interface

Enhanced magnetic behavior of LaFeO3 by co-doping with Nd3+ and V5+ substitution (La0.8Nd0.2Fe0.95V0.05O3)

To enhance the quality of applications of LaFeO3 (LFO) as a magnetoelectric multiferroic through the improvement of magnetic behaviour, co-doping of Nd3+ (20 %) and V5+ (5 %) was considered for partial substitution in place of La3+ and Fe3+, respectively. Co-doped sample of La0.8Nd0.2Fe0.95V0.05O3 (LNFVO) was prepared by solid state reaction method. Rietveld analysis of X-ray diffractograms confirmed the formation as well as successful incorporation of dopants (Nd3+ and V5+) in La3+ and Fe3+ sites of the distorted perovskite structure with Pbnm space group. Morphological features including information related to crystallographic phase were examined by TEM. Distortion due to co-doping helped to achieve the stated objectives. Valence states of dopants and host cations were explored by analyzing XPS observations. Detailed magnetic measurements in the temperature range starting from 300 K down to 2 K suggested that magnetic property was drastically enhanced compared to that of the undoped, which was attributed to mismatch of valence states, ionic diameters etc. between dopants with host cations. The doped sample showed antiferromagnetic to ferromagnetic transition at and below 19 K. All such findings related to magnetic property would be quite attractive for the improvement of multiferroic applications as the low value of magnetization of pristine sample of LFO restrict it to become a good magnetoelectric multiferroic.

Investigation of the structural, Electronic and magnetic properties of Mn2PdSn Heusler alloy under hydrostatic pressure

The pressure effect on the structural, electronic and magnetic properties of Mn2PdSn Heusler alloy was investigated by the first-principles full-potential linearized augmented plane wave (FP-LAPW) method based on density functional theory (DFT). The exchange and correlation function has been chosen using generalized gradient approximation (GGA) within the parameterization of Perdew-burke-ernzerhof. The lattice constant, electronic density of state (DOS), and magnetic properties such as total magnetic moment were obtained under pressure. It was determined that the calculated lattice parameters are in good agreement with the literature. The Mn2PdSn is stable in the Hg2CuTi-type structure. Furthermore, we expect an extraordinary occurrence of pressure-induced metallic ferrimagnetism to half-metallic ferromagnetism transition in the cubic phase of Mn2PdSn alloy at hydrostatic pressures of 10 GPa.

A new S = 2 kagomé lattice compound with ferromagnetic behaviors

A new compound NaMn3(SeO3)2(HSeO3)6 was obtained by a conventional hydrothermal method. This compound crystallizes in a trigonal system with space group R-3, exhibiting a typical kagomé structure, where the kagomé layers are composed of [MnO6] octahedra linked by [SeO3] groups. Magnetic susceptibility measurements confirm that this compound exhibits a ferromagnetic transition at ∼13 K, as further confirmed by the heat capacity data. The magnetic entropy was estimated, indicating that the system may release almost the entire entropy at low temperature.

Investigation of the structural and magnetic properties of the GdCoC compound featuring excellent cryogenic magnetocaloric performance

Magnetic refrigeration (MR) based on the magnetocaloric effect (MCE) has been recognized as an environmentally benign and energy-efficient cooling technology. Exploring suitable magnetocaloric materials is a crucial prerequisite for practical MR applications. We have herein provided a systematic investigation of the crystal structure, microstructure, electronic structure, magnetic phase transition, critical behavior, and MCE of the GdCoC compound featuring excellent cryogenic magnetocaloric performance by means of experimental determination and theoretical calculation. The GdCoC compound is crystallized in a simple layered tetragonal crystal structure with a P42/mmc space group and undergoes two successive ferromagnetic (FM) transitions along with a low-temperature weak antiferromagnetic (AFM) transition under low magnetic fields. Density functional theory calculations confirms the FM coupling of the Gd and Co intra-sublattice interactions, whereas AFM coupling for their inter-sublattice interaction. The magnetic transitions are merged in to one under high magnetic fields which has been confirmed to be second-order type and its critical behavior can be understood in the framework of tri-critical mean-field model, whereas the low-temperature weak AFM transition is belonging to the first-order type. The excellent magnetocaloric performance of the GdCoC compound was identified by the parameters of magnetic entropy change, adiabatic temperature change, temperature-averaged entropy change, relative cooling power, and refrigerant capacity, which are superior to most of the well-known magnetocaloric materials with similar working temperatures, making it attractive for practical cryogenic MR applications.

Magneto-transport and thermoelectric studies of antiperovskite semimetal: Mn3SnC

We explore the magnetotransport and thermoelectric (Seebeck and Nernst coefficients) properties of Mn3SnC, an antiperovskite magnetic Nodal line semimetal. Mn3SnC shows paramagnetic (PM) to concurrent antiferromagnetic (AFM)/ferromagnetic (FM) transition at T ∼ 286 K. The electrical resistivity and Seebeck coefficient indicate the importance of electron–magnon scattering in the concurrent AFM/FM regime. We observed a large positive magnetoresistance (MR) of ∼8.2 at 8 T field near magnetic transition, in the otherwise negative MR behaviour for low temperatures. The electrical resistivity and MR show a weak thermal hysteresis around the boundary of transition temperature and the width of hysteresis decreases as magnetic field increases. Interestingly the Hall and Seebeck coefficients change sign from positive to negative below the transition temperature, highlighting the different scattering for holes and electrons in this multi-band system. The Seebeck and Nernst signal exhibit two sharp anomalies; one at the transition temperature and another at ∼50 K. The anomaly at magnetic transition in the Nernst signal disappear at 8 T magnetic field, owing to the reduction of magnetic fluctuation. A pseudo-gap near the Fermi level produces an upturn with a broad minimum in the Seebeck signal.

EXPLORING THE INFLUENCE OF B-SITE DOPANTS ON STRUCTURAL AND MAGNETIC PROPERIES IN La0.8Ag0.2Mn1-XCoxO3 (x: 0 and 0.1) COMPOUNDS

This study examines the structural, electrical, magnetic, and magnetocaloric properties of La0.8Ag0.2Mn0.9A0.1O3 (A: Mn, and Co) compounds under doping in the B-site. XRD results show that the compound containing Co ions directly replaced Mn ions in the B-site without forming a secondary phase containing higher metallic Ag impurities. The data obtained using Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS), the temperature dependence of magnetization (M-T), the magnetic field dependence of magnetization (M-H), and the magnetic entropy change (SM) analysis reveal the effect of the doped element on the magnetic properties of the compounds due to the changes they create in the structural and Mn3+/Mn4+ ratio. It has been determined that the paramagnetic to ferromagnetic transition temperature (Curie temperature, TC) of the La0.8Ag0.2Mn0.9Co0.1O3 (LAMO-Co) is quite lower than the LAMO.

Large magnetocaloric effect and giant magnetoresistance in rare earth based intermetallic compound ErAl3: construction of magnetic phase diagram

This study explores the magnetic and magnetotransport behavior of polycrystalline ErAl3 compound. The polycrystalline compound adopts HoAl3-type structures with the R-3m space group, No. 166-2 and hR60 configurations. Multiple magnetic orderings and two field-induced metamagnetic transitions are observed. ErAl3 exhibits a significant magnetocaloric effect (MCE), −ΔSM = 15.25 J kg−1 K−1 and high relative cooling power of 383 J kg−1 with applied magnetic field change (ΔH) of 70 kOe near the paramagnetic to ferromagnetic transition, showcasing its potential for magnetic refrigeration technology. The compound also demonstrates metallic behavior, with a notable magnetoresistance of 48.5 % at 2 K due to the suppression of antiferromagnetism. The magnetic phase diagram reveals four distinct phases influenced by temperature and magnetic field, identified through the study of the MCE.

Out‐of‐Plane Superexchange Interaction Enhanced Ferromagnetism in Semiconducting Monolayer Cr2Se3

Abstract2D magnetic semiconductors exhibit great potential for next‐generation spintronics, but realizing their full capabilities has been hindered by the low Curie temperatures (Tc) below 50 K observed in current materials. Here, a new mechanism to substantially enhance the Tc of 2D semiconducting materials through incorporating both in‐plane and out‐of‐plane superexchange interactions enabled by structural design is demonstrated. Specifically, monolayer Cr2Se3 is synthesized with a five‐layer Se–Cr–Se–Cr–Se atomic structure using molecular beam epitaxy (MBE). This unique structure not only possesses optimized in‐plane superexchange interaction but also incorporates out‐of‐plane Cr–Se–Cr couplings. Scanning tunneling spectroscopy (STS) and angular‐resolved photoemission spectroscopy (ARPES) confirm its semiconducting nature. Remarkably, the ferromagnetic phase transition observed by ARPES and Magnetic Force Microscopy (MFM) indicated that its Tc is up to 230 K. This not only establishes a new record for Tc in 2D ferromagnetic semiconductor materials but also introduces a novel approach to modulating materials' properties by manipulating the vertical dimension in 2D materials.

Role of Griffiths phase on magnetocaloric properties and critical behavior of half-doped manganites [La0.5Sr0.5-xCaxMnO3(x = 0, 0.25, 0.5)

In this article, a comprehensive study of the effect of calcium substitution on structural magnetic, magnetocaloric properties, and role of Griffiths phase on magnetocaloric properties of half-doped manganites La0.5Sr0.5-xCaxMnO3(x=0,0.25,0.5)] have been presented. A structural phase transition I4/mcm - Pbnm is observed in the whole series. The system exhibits two magnetic transitions for Ca-00 and Ca-25, whereas only one phase transition is observed for Ca-50. Paramagnetic (PM)-ferromagnetic (FM) transition is observed in the whole series and ferromagnetic (FM) - antiferromagnetic (AFM) phase transition is only observed in Ca-25. Interestingly, short range FM clusters exist in the PM matrix of Ca-50, which is a signature of Griffiths phase (GP). The confirmation of GP has been carried out by performing iso-field magnetization measurements at 200 Oe, 500 Oe, and 1 kOe, respectively. Further magnetocaloric properties have been discussed on the basis of isothermal magnetization curves recorded at certain temperature intervals. Calcium substitution favors the enhancement of magnetic entropy change in the series, especially for Ca-50, a magnetic entropy change of 4.5J/(kgK) with relative cooling power of 180J/kg under 5T magnetic field was observed. Iso-field magnetization and magnetocaloric effect along with critical behavior analysis have been carried out to probe the GP and other inhomogeneities present in the respective series.

Critical behaviors of van der Waals itinerant ferromagnet Fe3.8GaTe2

The critical behavior of the van der Waals ferromagnet Fe3.8GaTe2 was systematically studied through measurements of isothermal magnetization, with the magnetic field applied along the c-axis. Fe3.8GaTe2 undergoes a non-continuous paramagnetic to ferromagnetic phase transition at the Curie temperature T c ∼ 355 K. A comprehensive analysis of isotherms around T c utilizing the modified Arrott diagram, the Kouvel–Fisher method, the Widom scaling law, and the critical isotherm analysis yielded the critical exponent of β= 0.411, γ = 1.246, and δ = 3.99. These critical exponents are found to be self-consistent and align well with the scaling equation at high magnetic fields, underscoring the reliability and intrinsic nature of these parameters. However, the low-field data deviates from the scaling relation, exhibiting a vertical trend when T < T c. This discrepancy suggests the occurrence of a first-order phase transition in the crystal under a low magnetic field when T< T c. Mössbauer spectra were employed to provide insights into the critical behaviors of magnetic moments at different sites, including (Fe1)A, (Fe1)B, and Fe2. The results are consistent with the isothermal magnetization analysis. Additionally, the renormalization group theory analysis reveals that the spin coupling within the Fe3.8GaTe2 crystal follows the three-dimensional Heisenberg ({d:n} = {3:3}) type with long-range magnetic and exchange interaction decays with a distance as J(r) ≈ r −4.80.

Magnetic properties of the Co-doped MnNiGe system in high magnetic field

High-field magnetic properties of the Co-doped MnNiGe system, Mn0.9Co0.1NiGe, which undergoes a ferromagnetic and structural phase transition at Tt= 215 K, were investigated. Additionally, first-principles calculations were performed on Mn0.875Co0.125NiGe. The magnetic field, μ0H, dependence of magnetization, M(μ0H), of Mn0.9Co0.1NiGe saturates at ∼73 A⋅m2⋅kg−1 below Tt and shows significant hysteresis in the range of 215 ≤T≤ 230 K due to the magnetic-field-induced structural phase transition. The isothermal magnetic entropy change, ΔS, peaks around Tt, reaches -79.7 J⋅K−1⋅kg−1 for Δμ0H = 30 T. The density of states (DOS) calculated for Mn0.875Co0.125NiGe in the paramagnetic-hexagonal phase (Tt<T) exhibits a peak at the Fermi energy, EF, with significant contributions from the Mn 3d orbitals. In the ferromagnetic-orthorhombic phase, DOS at EF is suppressed, indicating that the structural phase transition at Tt in this system is primarily driven by the band Jahn-Teller effect.

Exploring the impact of non-magnetic ion Mg2+ into M- type Ba0.5Ca0.5Fe12-xO19 (x = 0.0, 0.1 and 0.2) hexaferrites on structural, magnetic and magnetocaloric effect properties

The Mg substituted Ba-Ca Hexaferrites Ba0.5Ca0.5Fe12-xMgxO19 (BCFMO) (x = 0.0, 0.1 and 0.2) were prepared through the conventional ceramic technology. The microstructure, morphology, magnetic and magnetocaloric Effect (MCE) of all samples were investigated by XRD, SEM, EDX and BS1 and BS2 magnetometer. XRD analysis revealed the formation of Magnetoplumbite structure with P63/mmc space group and minor secondary phase R-3 m and having crystallites in the range of 121–108 nm. The XRD refinement indicates a preference for Mg2+ ions to occupy the octahedral 12k site. SEM analysis showed the presence of the hexagonal shape for all products. The saturation magnetization Ms decreases from 69.77 to 65.55 emu/g and the coercive field Hc increases from 1.29 to 3.54 kOe with the increase in Mg concentration. The increase of Hc with increasing Mg concentration is attributed to the reduction in crystallite sizes. Additionally, the magnetocrystalline anisotropy parameters (obtained by the "Law of Approach to Saturation method") such as the anisotropy field (Ha) and the effective magnetic anisotropy constant (Keff) were found to be 16.59–24.18 kOe and 5.15–6.94 105 emu/cm for x = 0.0–0.2, respectively.The MFC-MZFC curves for all compounds show a paramagnetic (PM) to ferromagnetic (FM) phase transition at the Curie Temperature TC. Doping with Mg2+ in BCFO lowers the Curie temperature TC down to T ∼700 K. The maximum entropy (-ΔSmmax) (x = 0.1) and the corresponding RCPmax (x = 0.2) at 5 T are found to be 1.80 J.kg-1.K-1 and 114.29 J.kg-1 respectively. The above results demontrate that the samples have great potential for permanent magnets and guide for the Magnetocaloric Effect (MCE) applications.

Critical behavior in the ferromagnet MgMn6Sn6 single crystal with HfFe6Ge6-type structure

A thorough investigation was carried out to analyze the magnetic critical properties of single crystals belonging to the HfFe6Ge6-type structure. MgMn6Sn6 exhibit a ferromagnetic transition below TC ≈ 300 K. The magnetization measurements were analyzed around the phase transition temperature of this ferromagnetic material for two different orientations: H//ab and H//c. Using Kouvel‐Fisher method, we can determine critical exponents β, γ, and δ in this study. To evaluate accuracy of these values, the scaling equation m=f±(h) and Widom scaling law δ=1+γ/β were applied. Critical exponents γ = 1.191 ± 0.007 at TC = 300.92 K, β = 0.326 ± 0.003 at TC = 300.96 K, and δ = 4.653 with TC ≈ 300 K indicate that the three-dimensional Ising model (β = 0.325, γ = 1.24, and δ = 4.82) is the better model for H//ab. The mean‐field and 3D‐Heisenberg models were the best models below TC and above TC for H//c, respectively. The MgMn6Sn6 single crystal exhibits a notable anisotropic transition in its magnetic phase according to all experimental findings. The presence of an anisotropic state with short-range order in the ferromagnetic system are revealed by analyzing electron spin resonance (ESR) spectroscopy. Our research provides experimental proof of a holistic comprehension regarding the magnetic phase-transition characteristics demonstrated by MgMn6Sn6.

Anisotropic magnetism and band evolution induced by ferromagnetic phase transition in titanium-based kagome ferromagnet SmTi3Bi4

Anisotropic magnetism and band evolution induced by ferromagnetic phase transition in titanium-based kagome ferromagnet SmTi3Bi4

Current orientation dependence of anisotropic magnetoresistance in SmCo[formula omitted]

Anisotropic magnetoresistance in a highly oriented SmCo5 device was systematically investigated at various temperatures. Currents were applied along the magnetic easy axis and the magnetic hard axis of SmCo5, and the corresponding anisotropic magnetoresistances were measublack, respectively. In both these instances, the anisotropic magnetoresistances exponentially decrease as the temperature increases. Notably, the anisotropic magnetoresistance magnitudes for the two instances intersect at 220 K. This intersection may relate to the compensation between the spin and orbital magnetic moments of Sm, which is also considered to be a hint of a ferromagnetic and ferrimagnetic transition in SmCo5. The results exhibit the capability to monitor magnetic configurations through magnetotransport properties, potentially facilitating the development of spintronic devices based on SmCo5.

Magnetic domain structures in ultrathin Bi2Te3/CrTe2 heterostructures

Abstract Chromium tellurium compounds are important two-dimensional van der Waals ferromagnetic materials with high Curie temperature and chemical stability in air, which is promising for applications in spintronic devices. Here, high-quality spin-orbital-torque (SOT) device, Bi2Te3/CrTe2 heterostructure was epitaxially grown on Al2O3 (0001) substrates. Anomalous Hall measurements indicate the existence of strong ferromagnetism in this device with the CrTe2 thickness down to 10 nm. In order to investigate its micromagnetic structure, cryogenic magnetic force microscope (MFM) was utilized to measure the magnetic domain evolutions at various temperatures and magnetic fields. The virgin domain state of the device shows a worm-like magnetic domain structure with the size around 0.6 ~ 0.8 µm. Larger irregular-shape magnetic domains (＞1µm) can be induced and pinned, after the field is increased to coercive field and ramped back to low fields. The temperature-dependent MFM signals exhibit a nice mean-field-like ferromagnetic transition with Curie temperature around 201.5 K, indicating a robust ferromagnetic ordering. Such device can be potentially implemented in future magnetic memory technology.

Evolution of anomalous Hall effect in ferromagnetic Weyl semimetal NbxZr1–xCo2Sn

Abstract Magnetic topological semimetal can host various topological non-trivial states leading to exotic novel transport properties. Here we report the systematic magneto-transport studies on the Heusler alloy Nb x Zr1−x Co2Sn considered as a ferromagnetic (FM) Weyl semimetal. The cusp anomaly of temperature-dependent resistivity and large isotropic negative magneto-resistivity (MR) emerge around the FM transition consistent with the theoretical half-metallic predictions. The prominent anomalous Hall effect (AHE) has the same behavior with the applied field along various crystal directions. The Nb doping introduces more disorder resulting in the enhancement of the upturn for the temperature-dependent resistivity in low temperatures. With Nb doping, the AHE exhibits systemic evolution with the Fermi level lifted. At the doping level of x = 0.25, the AHE mainly originates from the intrinsic contribution related to non-trivial topological Weyl states.

Anomalous Hall effect and magnetic transition in the kagome material YbMn6Sn6

We investigate the magnetic and transport properties of a kagome magnet YbMn6Sn6. We have grown YbMn6Sn6 single crystals having a HfFe6Ge6 type structure with ordered Yb and Sn atoms, which is different from the distorted structure previously reported. The single crystal undergoes a ferromagnetic phase transition around 300 K and a ferrimagnetic transition at approximately 30 K, and the magnetic transition at low temperature may be correlated to the ordered Yb sublattice. Negative magnetoresistance has been observed at high temperatures, while the positive magnetoresistance appears at 5 K when the current is oriented out of kagome plane. We observe a large anisotropic anomalous Hall effect with the intrinsic Hall contribution of 141 Ω−1cm−1 for σzxint and 32 Ω−1cm−1 for σxyint , respectively. These values are similar to those in YMn6Sn6 with the same anisotropy. The magnetic transition and anomalous Hall behavior in YbMn6Sn6 highlights the influence of the ordered Yb atoms and rare earth elements on its magnetic and transport properties.