Antiferromagnetic Arrangement Research Articles

Long-range magnetic order in CePdAl3 enabled by orthorhombic deformation

We investigate the effect of structural deformation on the magnetic properties of orthorhombic CePdAl3 in relation to its tetragonal polymorph. Utilizing x-ray and neutron diffraction, we establish that the crystal structure has the Cmcm space-group symmetry and exhibits pseudotetragonal twinning. According to density functional calculations, the tetragonal-orthorhombic deformation mechanism has its grounds in the relatively small free enthalpy difference between the polymorphs, allowing either phase to be quenched, and fully accounts for the twinned microstructure of the orthorhombic phase. Neutron diffraction measurements show that orthorhombic CePdAl3 establishes long-range magnetic order below TN=5.29(5) K characterized by a collinear, antiferromagnetic arrangement of magnetic moments. Magnetic anisotropies of orthorhombic CePdAl3 arise from strong spin-orbit coupling as evidenced by the crystal-field splitting of the 4f multiplet, fully characterised with neutron spectroscopy. We discuss the potential mechanism of frustration posed by antiferromagnetic interactions between nearest neighbors in the tetragonal phase, which hinders the formation of long-range magnetic order in tetragonal CePdAl3. We propose that orthorhombic deformation releases the frustration and allows for long-range magnetic order. Published by the American Physical Society 2024

Investigating the dilute magnetic semiconductor behavior of 4d transition metal adsorption on B4C3

We conducted a systematic investigation of B4C3 adsorbed with 4d-transition metals (4d-TMs), including Tc, Cd, Mo, Nb, Rh, Ru, and Ag, using first principles. This study involved an evaluation of structural, electronic, and magnetic properties. When single atom adsorption was adsorbed to B4C3 using elements such as Tc, Nb, Rh, Ru, and Ag, it demonstrated characteristics of a diluted magnetic semiconductor (DMS), manifesting magnetic moments. Conversely, Cd, Mo, and Pd exhibited behavior consistent with non-magnetic semiconductors. Ferromagnetic (FM) and antiferromagnetic (AFM) arrangements were formed through the adsorption of 2TM atoms on B4C3. In the FM setup, Ru and Nb uphold their roles as DMS. Interestingly, Tc and Rh exhibit half-metal behavior in this configuration, displaying their potential utility in spintronics applications. In the AFM configuration, Tc displayed half-metallic behavior, while the other metals maintained the same characteristics observed in the case of single TM adsorption. The reactivity of Nb-B4C3 is notably high owing to its low work function, whereas Cd-B4C3 is observed to be less reactive. AFM coupling is favorable in the 2Nb-, 2Rh-, and 2Ru-B4C3 systems, while 2Tc-B4C3 displays FM coupling. Transition metals belonging to the 4d series hold the potential to enhance the properties of B4C3, including its half-metallic, metallic, and semiconductor characteristics. These findings suggest the potential use of 4D transition metals adsorbed on B4C3 as a prospective material for spintronics and magnetic storage applications in the future.

Signatures of nearly compensated magnetism and spin glass behavior in highly frustrated β-Mn-type Mn50Fe25+xAl25-x Heusler alloys.

The present study examines the effect of Fe/Al concentration on the structural and magnetic properties of Mn-rich Mn50Fe25+xAl25-x (x = 5, 10, 15) Heusler alloys through x-ray diffraction, temperature- and field-dependent DC magnetization, thermoremanent magnetization, magnetic memory effect, AC susceptibility measurements, and DFT calculations. The samples crystallize in a cubic β-Mn structure. The trend shows a reduction in lattice parameters (unit cell volume) with the increasing Fe proportion. These alloys exhibit strong antiferromagnetic interactions with large frustration parameters, indicating the presence of competing magnetic interactions. The DC magnetization data reveal spin glass-like features with a peak at spin glass freezing temperature (Tf). The observation of bifurcation in temperature-dependent zero-field-cooled and field-cooled magnetization curves, exponential dependence of the temperature variation of remanence and coercivity, magnetic relaxation, and magnetic memory effect below Tf support the spin-glass character of these alloys. The frequency dependence of Tf is also examined in the context of dynamic scaling laws, such as the Vogel-Fulcher law and critical slowing down model, which further supports the presence of spin glass behavior. In the theoretical DFT calculations, the electronic structure is found to be metallic and similar for both spin projections. Moreover, the antiferromagnetic arrangement of the magnetic moments, in line with the experimental observations, is stabilized by exchange interactions, resulting in an almost compensated total magnetic moment of 0.02-0.38µB/f.u. This is probably caused by the frustrated structure and non-stoichiometric compositions of Mn50Fe25+xAl25-x.

Spin Coupling in the Initial Stages of the Zinc‐Blende MnN Growth on the CrN (111) Surface

AbstractSpin‐polarized first‐principles calculations are carried out to study the structural, electronic, and magnetic properties of the MnN growth on the CrN (111) surface. Different magnetic configurations between Mn‐deposited atoms and the substrate are considered. The H3 site is the most favorable site for the adoption and incorporation cases and the Mn spins switch from paramagnetic to antiferromagnetic arrangement. The minimum energy pathway for the Mn diffusion is calculated, showing magnetic modifications in the substrate. A structural transition from tetragonal rock‐salt to zinc‐blende (ZB) structure as the number of MnN deposited layers increases is noticed. Thermodynamic analysis demonstrates that the growth of MnN on CrN is feasible. The density of states for an MnN layer with an extra nitrogen layer shows a half‐metallic behavior and the remaining structures exhibit a metallic character. The ZB‐MnN structures have an antiferromagnetic behavior with a metallic character. Magnetic anisotropy energies reveal a switching of easy magnetization axis, from in‐plane to out‐of‐plane with the formation of MnN on the surface. These results suggest that the CrN/ZB‐MnN system may be employed in antiferromagnetic spintronics applications as the fabrication of perpendicular magnetic tunnel junctions.

Theoretical study of the complex antiferromagnetic Heusler alloys Pd[formula omitted]MnAl, Pd[formula omitted]MnIn, and Pt[formula omitted]MnAl

The complex antiferromagnetic (AFM) phases displayed by the Heuser alloys Pd2MnAl, Pd2MnIn, and Pt2MnAl, are theoretically studied. The crystalline structure, electronic, and magnetic properties are calculated within the ab initio density functional theory. The super unit cell considered to describe the various magnetic arrangements contains 128 atoms. We analyzed the ferromagnetic (FM) and the three different antiferromagnetic (AFM) phases and found that the Pd2MnAl crystalline structure is orthorhombic with dimensions 6.055, 6.461, 6.026 Å. The AFM state with the lowest energy is the AFM3 with a Mn magnetic moment of 3.813 μB. The Pd2MnIn crystallizes in an orthorhombic structure with lattice parameters 6.249, 6.763, 6.227 Å. The ground state antiferromagnetic arrangement is also of type 3 with a Mn magnetic moment of 3.932 μB. The Pt alloy crystallizes in an orthorhombic structure with lattice dimensions of 6.029, 6.906, and 5.683 Å. In this case, the antiferromagnetic ground state is of type 1 with a Mn magnetic moment of 3.716 μB. The Pd and Pt d states are deep in energy and do not interact much with the Mn d states. This produces, in Pd and Pt, no magnetic polarization.

Investigating the thermal properties of CrN: Theoretical insights and real ceramics

Ab-initio calculations of lattice heat capacity and phonon thermal conductivity have been performed for CrN of rock-salt structural type (paramagnetic) and for the orthorhombic antiferromagnetic (AFM) phase below TN ≈ 285 K. The comparison with experimental data below ≈30 K unveils that in contrary to the theoretically calculated heat capacity following the βT3 term with Debye temperature ΘD = 830 K, a large excess of experimental heat capacity in a form of δT2 is observed. This additional heat capacity is ascribed to magnons in the specific layered-type AFM arrangement of CrN. The experimental thermal conductivity shows a similar low-temperature excess of T2-dependence. Considering that mean free path of heat carriers is essentially limited by the grain size and calculated phonon conductivity itself is very low below ≈30 K, such additional contribution can be ascribed again to AFM magnons though theoretical model of such conductivity is still to be assessed. In spite of this complexity, our model of phonon thermal conductivity reproduces well the maximum of 7.2 Wm−1K−1 at 150 K followed by a decline tied to phonon-phonon scattering (Umklapp process). Nonetheless at higher temperatures, the experimental data evidence sudden drop at TN to ≈2 Wm−1K−1 with only slightly varying thermal conductivity at elevated temperatures, which reminds rather a behavior of amorphous or defective solids. It is proposed that atomic displacements that stabilize spin-parallel and spin-antiparallel Cr pairs in the orthorhombic AFM phase persist partially as fluctuating ones in the cubic paramagnetic state above TN, which gives rise to dynamic strain fields that cause strong phonon scattering.

Analysis of metamagnetic transitions in antiferromagnetic arrangements in the RRhIn5 (R[dbnd]Nd, Tb, Dy, and Ho) series using a four sublattice model

The RRhIn5 (RNd, Tb, Dy, and Ho) series of compounds crystallizes in the Ho2CoGa8 tetragonal type-structure, with P4/mmm space group. A Hamiltonian model of four magnetic sublattices is used to reproduce the metamagnetic transitions of these series, considering the crystalline electric field interaction and the exchange interaction in the molecular field approximation. The crystalline electric field parameters were extracted from literature sources, while the exchange parameters were adjusted to optimize the agreement between the proposed model and the experimental data. The four sublattice model presented here successfully describes the metamagnetic transitions that appeared, at the low magnetic fields, in the RRhIn5 (RNd, Tb, Dy, and Ho) series, in contrast to other molecular field model found in the literature that inadequately reproduces these transitions.

Unusual magnetic properties of (Sr, Mn)-substituted BiFeO3 near the polar/antipolar phase boundary

Investigations of the crystal structure and magnetic properties of the Bi0.85Sr0.15Fe1-xMnxO3 (0.1 ≤ x ≤ 0.5) ferromanganites were carried out. The materials maintain the single-phase polar R3c structure of the pure bismuth ferrite up to x = 0.35 (a further increase in the Mn content stabilizes the antipolar Pnam phase), thus exhibiting the coexistence of spontaneous polarization and magnetic order over a wide range of Mn concentrations, sufficient to influence the cycloidal antiferromagnetic arrangement typical of the parent compound and contribute to the canted antiferromagnetic phase formation (at room temperature). A complex magnetic behaviour with irregular changes in remanent magnetization and coercive field suggesting the temperature-driven modification of the canted antiferromagnetic structure near the polar/antipolar phase boundary has also been found.

Interplay of Magnetic Interaction and Electronic Structure in New Structure RE-12442 Type Hybrid Fe-Based Superconductors

We present detailed first-principles density functional theory-based studies on RbRE2Fe4As4O2 (RE = Sm, Tb, Dy, Ho) hybrid 12442-type iron-based superconducting compounds with particular emphasis on competing magnetic interactions and their effect on possible magneto-structural coupling and electronic structure. The stripe antiferromagnetic (sAFM) pattern across the xy plane emerges as the most favorable spin configuration for all the four compounds, with close competition among the different magnetic orders along the z-axis. The structural parameters, including arsenic heights, Fe-As-Fe angle, and other relevant factors that influence superconducting Tc and properties, closely match the experimental values in stripe antiferromagnetic arrangement of Fe spins. Geometry optimization with inclusion of explicit magnetic ordering predicts a spin–lattice coupling for all the four compounds, where a weak magneto–structural transition, a tetragonal-to-orthorhombic structural transition, takes place in the relaxed stripe antiferromagnetic spin configuration. Absence of any experimental evidence of such structural transition is possibly an indication of nematic transition in RE-12442 compounds. As a result of structural distortion, the lattice contracts (expands) along the direction with parallel (anti-parallel) alignment of Fe spins. Introduction of stripe antiferromagnetic order in Fe sub-lattice reconstructs the low-energy band structure, which results in significantly reduced number of bands crossing the Fermi level. Moreover, the dispersion of bands and their orbital characteristics also are severely modified in the stripe antiferromagnetic phase similar to BaFe2As2. Calculations of exchange parameters were performed for all the four compounds. Exchange coupling along the anti-parallel alignment of Fe spins J1a is larger than that for the parallel aligned spins J1b. A crossover between the super-exchange-driven in-plane next-nearest-neighbor exchange coupling J2 and in-plane exchange coupling J1a due to lanthanide substitution was found. A large super-exchange-driven next-nearest-neighbor exchange interaction is justified using the construction of 32 maximally localized Wannier functions, where the nearest-neighbor Fe-As hopping amplitudes were found to be larger than the nearest- and the next-nearest-neighbor Fe-Fe hopping amplitudes. We compare the hopping parameters in the stripe antiferromagnetic pattern with non-magnetic configuration, and increased hopping amplitude was found along the anti-parallel spin alignment with more majority-spin electrons in Fe dxz and dxy but not in Fe dyz. On the other hand, the hopping amplitudes are increased in stripe antiferromagnetic phase along the parallel spin alignment with more majority-spin electrons in only Fe dyz. This difference in hopping amplitudes in the stripe antiferromagnetic order enables more isotropic hopping.

Ferromagnetic coupling mechanism and vacancy defect regulation strategy of V-doped LiMgAs

First-principles calculations were conducted to investigate the electronic structure and magnetic coupling mechanism of V-doped LiMgAs. The regulation strategy of Li vacancy defects on magnetism was also adopted. The results showed that all the designed defective configurations exhibited thermodynamic stability evaluated from the formation energy. The V nearest neighbor doping configuration occupied the lowest formation energy of −9.26eV and performed the strongest stability. V dopant had advantages in magnetic introduction and the maximum atomic magnetic moment in this study was 6.40 μB/V. The ground state of the magnetic coupling was determined by the energy difference of the doping configurations for magnetic ions antiferromagnetic and ferromagnetic arrangements. The magnetic dopants existed in Li(MgV)As system by ferromagnetic coupling and the ferromagnetic stability weakened with the increase of the V atom separation. The incorporation of Li vacancy defect promoted the enhancement of ferromagnetism. The optimal design configuration was V atoms nearest neighbor doping with one Li vacancy defect with the energy difference of 0.27eV, which performed the strongest ferromagnetic stability. The removal of Li ion introduced the additional itinerant hole carrier and elevated the non-localized characteristics of the carriers in p-d hybrid orbitals, which facilitated the electron exchange between magnetic ions. In this paper, a novel type of dilute magnetic semiconductor with controllable carriers was designed and the mechanism of ferromagnetic coupling was revealed, which provided a theoretical reference for the subsequent studies.

Solution-Processed NiPS3 Thin Films from Liquid Exfoliated Inks with Long-Lived Spin-Entangled Excitons.

Antiferromagnets are promising materials for future opto-spintronic applications since they show spin dynamics in the THz range and no net magnetization. Recently, layered van der Waals (vdW) antiferromagnets have been reported, which combine low-dimensional excitonic properties with complex spin-structure. While various methods for the fabrication of vdW 2D crystals exist, formation of large area and continuous thin films is challenging because of either limited scalability, synthetic complexity, or low opto-spintronic quality of the final material. Here, we fabricate centimeter-scale thin films of the van der Waals 2D antiferromagnetic material NiPS3, which we prepare using a crystal ink made from liquid phase exfoliation (LPE). We perform statistical atomic force microscopy (AFM) and scanning electron microscopy (SEM) to characterize and control the lateral size and number of layers through this ink-based fabrication. Using ultrafast optical spectroscopy at cryogenic temperatures, we resolve the dynamics of photoexcited excitons. We find antiferromagnetic spin arrangement and spin-entangled Zhang-Rice multiplet excitons with lifetimes in the nanosecond range, as well as ultranarrow emission line widths, despite the disordered nature of our films. Thus, our findings demonstrate scalable thin-film fabrication of high-quality NiPS3, which is crucial for translating this 2D antiferromagnetic material into spintronic and nanoscale memory devices and further exploring its complex spin-light coupled states.

Dynamical Stability and Physical Properties of Fe Dihalide Nanowires

AbstractAn extensive first‐principles and atomistic Monte Carlo study on isolated Fe ( = F, Cl, Br, I) nanowires is presented. The structural properties of the Fe chains are determined and compared with their bulk structures. The results indicate that in the lowest energy configuration, the wires crystalize in a system that belongs to the space group (No. 131, Z = 2, point group ), with antiferromagnetic arrangement. The stability is determined by calculating the phonon frequencies in the whole Brillouin zone within the supercell approach. The relative stability of the periodic chains is also determined by calculating the elastic properties and comparing them with bulk cases. The band structure, the density of states, the magnetic properties, the anisotropy energy, and topological analysis, performed with the Quantum Theory of Atoms in Molecules approach, are also reported and discussed. The results support the idea that these Fe nanowire systems are promising materials for practical applications, like lithium‐ion batteries.

Magnetic structure and crystal field states ofPr2Pd3Ge5:μSRand neutron scattering investigations

We present the results of muon spin relaxation ($\ensuremath{\mu}\mathrm{SR}$), neutron powder diffration (NPD), and inelastic neutron scattering (INS) investigations on polycrystalline ${\mathrm{Pr}}_{2}{\mathrm{Pd}}_{3}{\mathrm{Ge}}_{5}$. The polycrystalline ${\mathrm{Pr}}_{2}{\mathrm{Pd}}_{3}{\mathrm{Ge}}_{5}$ is known to exhibit two antiferromagnetic transitions near ${T}_{\mathrm{N}1}=8.3$ K and ${T}_{\mathrm{N}2}=7.5$ K which is confirmed by the heat capacity measurements on the present sample. In the magnetically ordered state the NPD data show clear evidence for magnetic Bragg peaks, which for $T<{T}_{\mathrm{N}2}$ could be indexed with a propagation vector k = (1, 0, 0), and with k = (1, 0, 0.07) for ${T}_{\mathrm{N}2}<T<{T}_{\mathrm{N}1}$. We have determined the magnetic structure and found a canted antiferromagnetic structure of ordered ${\mathrm{Pr}}^{3+}$ moments. At 7.6 K we find an amplitude modulated incommensurate antiferromagnetic arrangement of ordered moments with a maximum ordered moment of 1.64(3) ${\ensuremath{\mu}}_{\mathrm{B}}$/Pr lying in the $ab$ plane tilted at about ${26}^{\ensuremath{\circ}}$ from the $b$ axis. At 1.8 K the antiferromagnetic structure is found to be commensurate with an ordered moment of 2.80(6) ${\ensuremath{\mu}}_{\mathrm{B}}$/Pr lying in the $ab$ plane tilted at about ${28}^{\ensuremath{\circ}}$ from the $b$ axis. Our zero-field $\ensuremath{\mu}\mathrm{SR}$ spectra at 1.5 K and at shorter time scale (below 0.5 $\ensuremath{\mu}\mathrm{s}$) reveal two oscillatory frequencies further supporting a long-range-ordered magnetic ground state. We have calculated the muon sites using the density functional theory calculation and present the results of internal field calculations at the muon stopping sites, which are in good agreement with the experimental observations. In the paramagnetic state, the INS data show three well defined CEF excitations near 8.0, 12.3, and 18.1 meV arising from the crystal electric field (CEF) split $J=4$ ground state of ${\mathrm{Pr}}^{3+}$. The CEF level scheme is deduced by analyzing the INS data by a model based on the CEF model.

Antiferromagnetism and Structure of Sr1−xBaxFeO2F Oxyfluoride Perovskites

Recently, a series of oxyfluorides, Sr1−xBaxFeO2F with x = 0, 0.25, 0.50, and 0.75 obtained through a novel synthesis route, were characterized by X-ray and neutron powder diffraction (NPD), magnetization measurements, and 57Fe Mössbauer spectroscopy (MS). The diffraction data revealed random occupancy of Sr and Ba atoms at the A-cation site, and a statistical distribution of O and F at the anionic sublattice of the perovskite-like structure specified in space group Pm-3m. MS spectra analysis consistently indicated the presence of Fe3+ ions at B-site, confirming the Sr1−xBaxFeO2F stoichiometry. Magnetic structure determination from the NPD data at room temperature established G-type antiferromagnetic arrangement in all compositions with Fe3+ moments of about 3.5 μB oriented along the c axis. In this study, we present and analyze additional NPD data concerning the low-temperature chemical and magnetic structure of Sr0.5Ba0.5FeO2F (x = 0.5) and SrFeO2F (x = 0). Basically, the three-dimensional G-type magnetic structure is maintained down to 2 K, where it is fully developed with an ordered magnetic moment of 4.25(5) μB/Fe at this temperature for x = 0.5 and 4.14(3) μB/Fe for x = 0. The data processing is complemented with a new approach to analyze the temperature dependence of the magnetic order TN on the lattice parameters, based on the magnetic hyperfine fields extracted from the temperature-dependent MS data.

Effect of Fe–Fe interactions and X-site vacancy ordering on the OH-stretching spectrum of foitite

Abstract. The OH-stretching infrared absorption spectrum of a tourmaline sample close to the foitite end-member is interpreted in the light of the density functional theory (DFT) modeling of iron-bearing Y3Z6 clusters in tourmaline. The iron-bearing clusters reflect the Al-rich and Na-deficient character of foitite and contain either two Fe2+ and one Al3+ or one Fe2+ and two Al3+ ions at the Y sites. The clusters are embedded in a tourmaline host structure with dravite composition. For the iron dimer models, the structural and vibrational properties corresponding to the ferromagnetic (FM) or anti-ferromagnetic (AFM) arrangement of the iron spins and the effect of vacancy ordering along the [001] axis are considered. A significant difference in the relaxed structure of the FM and AFM clusters is observed, stemming from the electron delocalization and Fe–Fe bonding interactions in the FM cluster. These bonding interactions are not allowed in the AFM cluster. In this case, the valence electrons with opposite spins remain separately localized on the two Fe atoms. The AFM configuration is more stable than the FM one in the theoretical models, provided that the description of the on-site Coulomb repulsion in Fe(3d) orbitals is improved within the DFT + U framework. Based on the theoretical results, the two bands at 3630 and 3644 cm−1 in the vibrational spectra of iron-rich and Na-deficient tourmalines are assigned to WOH groups associated with YFe22+YAl3+ environments with an AFM coupling of Fe ions and surrounded by one and two vacant X sites, respectively. The two major VOH bands of the experimental spectrum are interpreted on the same basis, and these interpretations are extrapolated to Mn-bearing tourmalines.

Bonding and Suppression of a Magnetic Phase Transition in EuMn2P2.

Electrons in solids often adopt complex patterns of chemical bonding driven by the competition between energy gains from covalency and delocalization, and energy costs of double occupation to satisfy Pauli exclusion, with multiple intermediate states in the transition between highly localized, and magnetic, and delocalized, and nonmagnetic limits. Herein, we report a chemical pressure-driven transition from a proper Mn magnetic ordering phase transition to a Mn magnetic phase crossover in EuMn2P2 the limiting end member of the EuMn2X2 (X = Sb, As, P) family of layered materials. This loss of a magnetic ordering occurs despite EuMn2P2 remaining an insulator at all temperatures, and with a phase transition to long-range Eu antiferromagnetic order at TN ≈ 17 K. The absence of a Mn magnetic phase transition contrasts with the formation of long-range Mn order at T ≈ 130 K in isoelectronic EuMn2Sb2 and EuMn2As2. Temperature-dependent specific heat and 31P NMR measurements provide evidence for the development of short-range Mn magnetic correlations from T ≈ 250-100 K, interpreted as a precursor to covalent bond formation. Density functional theory calculations demonstrate an unusual sensitivity of the band structure to the details of the imposed Mn and Eu magnetic order, with an antiferromagnetic Mn arrangement required to recapitulate an insulating state. Our results imply a picture in which long-range Mn magnetic order is suppressed by chemical pressure, but that antiferromagnetic correlations persist, narrowing bands and producing an insulating state.

Structural, Magnetic and Vibrational Properties of Van Der Waals Ferromagnet CrBr3 at High Pressure

The crystal and magnetic structures of van der Waals layered ferromagnet CrBr3 were studied using X-ray powder diffraction and neutron powder diffraction at pressures up to 23 GPa at ambient temperature and up to 2.8 GPa in the temperature range 6-300 K, respectively. The vibration spectra of CrBr3 were studied using Raman spectroscopy at pressures up to 23 GPa at ambient temperature. The anomalous pressure behavior of structural parameters and vibrational modes was observed, associated with a gradual isostructural phase transition in the pressure range 2.5-7 GPa. The Curie temperature TC reduced rapidly with a pressure coefficient dTC/dP=-4.1(4) K/GPa. A full suppression of the ferromagnetic state was expected at PC~8.4 GPa, where onset of the antiferromagnetic spin arrangement or magnetically disordered state may take place. Anomalies in Raman spectra at P~15 GPa point to another possible phase transformation in CrBr3, which may be related to the proximity of metallization of this van der Waals ferromagnet.

Tuning the Magnetic Properties of Cr2TiC2Tx through Surface Terminations: A Theoretical Study.

Recently, magnetic two-dimensional Cr2TiC2Tx MXenes with promising applications in spin electronics have been experimentally confirmed. However, the underlying magnetic mechanism needs to be further investigated. Along these lines, in this work, the magnetic properties of Cr2TiC2On/4F2-n/4 and Cr2TiC2On/4 structures were simulated through first-principle calculations using the GGA+U approach. The values of 4.1 and 3.1 eV were calculated for the Hubbard U of Cr and Ti, respectively, by applying the linear response method. Interestingly, the Cr2TiC2On/4F2-n/4-based configurations with low O content (n ≤ 4) exhibit antiferromagnetic behavior, while the majority of the respective configurations with high O content (n ≥ 5) are ferromagnetic. As far as the Cr2TiC2O5/4F3/4 structure (n = 5) is concerned, the value of about 2.64 μB was estimated for the magnetic moment of the Cr atom. On top of that, the Curie temperature lies within the range of 10~47 K. The extracted theoretical results are in good agreement with experimental outcomes of the Cr2TiC2O1.3F0.8-based structure. From the simulated results, it can be also argued that the magnetic moment of Cr atoms and the Neel temperature can be directly tuned by the active content of O atoms. The conductivity of both Cr2TiC2On/4F2-n/4 and Cr2TiC2On/4 configurations can be regulated by the externally applied magnetic field, while the density of states around the Fermi level shifted significantly between ferromagnetic and antiferromagnetic arrangements. The acquired results provide important theoretical insights to tuning the magnetic properties of Cr2TiC2Tx-based structures through surface termination mechanisms, which are quite significant for their potential applications in spin electronics.

Structural and magnetic properties of LaVO3 - Absence of anomalous diamagnetism

The novel magnetic and structural properties of LaVO3 have been studied in a comprehensive manner using X-ray and neutron powder diffraction, thermogravimetric analysis, X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, electrical transport, and dc magnetization. The lattice parameters have been found to be larger than previously reported, indicating the possibility of a novel phase. For vanadium ions, the valence state is found to be in accordance with the expected value (+3), the effect of larger lattice parameters is also present in the X-ray absorption spectroscopy measurement. Magnetic transition due to the antiferromagnetic ordering of the vanadium sublattice is observed at 142 K (TN). It undergoes a transition to a monoclinic crystal structure below 140 K (Tt). Negative magnetization (anomalous diamagnetism), which has been reported in earlier studies on the magnetic properties of LaVO3, is not observed in the present study. In the M − H isotherms, the ferromagnetic component of vanadium spins is absent. Below TN, the estimated magnetic structure of vanadium sublattice from powder neutron diffraction measurements is C-type antiferromagnetic, which persists in the entire low temperature region. The observed novel structural phase gives rise to pure C-type antiferromagnetic arrangement without weak ferromagnetic component. Theoretical calculations have been carried out to understand the nature of the magnetic ground state.

Electric-field control of magnetization reversal at room temperature in SmFeO3 single-phase multiferroic thin film

Rare-earth orthoferrite SmFeO3 (SFO) is a promising single-phase multiferroic material because of simultaneous coexistence of magnetic and ferroelectric orders at room temperature (RT). However, the spin structures within this bulk material are antiferromagnetic arrangements, and the magnetoelectric (ME) coupling effect is weak. Thus, the realization of electric control of magnetization reversal at RT remains challenging. In this work, SFO thin films with different thicknesses of 30 nm, 60 nm and 90 nm were constructed onto LaNiO3 (LNO)-buffered LaAlO3 (LAO) substrates by pulsed laser deposition (PLD) method. The X-ray diffraction (XRD) θ-2θ scans and reflection high-energy electron diffraction (RHEED) patterns demonstrate the SFO is perfect growth along the LAO (00 l) direction. Besides, the magnetic measurement results indicate that all the thin films are induced obvious RT ferromagnetism by compressive strain of substrates. More importantly, when providing a pair of opposite polarization voltages of± 2.5 V for the 90 nm thin film, the ferroelectric and induced ferromagnetic domains at the same local area can realize synchronous reversal, which shows that the SFO thin film under compressive strain is a rare ferromagnetic-based ME multiferroic material at RT. This kind of material will produce wide application prospect in future electric-write magnetic-read high-density memories and other spintronics devices.