Ferromagnetic Moment Research Articles

Comparative study of the magnetic phase diagrams and spin-flop-driven magnetodielectric responses of the pure and Mn3+-doped Pb2Fe2Ge2O9 single crystals

The Pb2Fe2-xMnxGe2O9 (x = 0.43) orthorhombic antiferromagnet single crystals have been synthesized by a modified pseudo-flux technique and their magnetic and magnetodielectric properties have been investigated. It has been established that partial substitution of highly anisotropic Mn3+ ions for iron ones significantly affects the magnetic structure of the crystal. Under magnetization of the crystal along the rhombic b and c axes, magnetization jumps have been detected, which are indicative of the occurrence of orientational transitions identified as first-order ones. No weak ferromagnetism characteristic of the pure crystal in the rhombic a axis direction has been detected. The field dependences of the magnetization for the pure and Mn-doped crystals have been analyzed using the thermodynamic potential that takes into account the crystal symmetry. It has been shown that, in the Mn-substituted crystal, the antiferromagnetic vector in the ground state is parallel to the rhombic b axis; in this state, weak ferromagnetism has not been observed. Under magnetization along the b axis, a conventional spin-flop transition occurs. The orientational transition under magnetization along the c axis has been attributed to the reorientation of the antiferromagnetic vector relative to the a axis with the simultaneous occurrence of a weak ferromagnetic moment along the c axis. Magnetic phase diagrams of the Mn-doped crystal for the magnetic fields H||b and H||c have been built.In the Mn-doped crystal, at E||c and H||c, the orientational transition-induced magnetodielectric response jump has been detected, which is higher than the jumps observed for the undoped crystal by a factor of 3. The magnetodielectric properties of the pure and Mn-doped crystals have been analyzed using their magnetic phase diagrams.

Ferromagnetic insulating behavior at low temperature induced by Sn doping in the ceramic SrRuO3

AbstractEffects of Sn doping at Ru site on the structural, magnetic, and transport behavior of polycrystalline SrRu1−xSnxO3 (x ≤ 0.1) have been investigated here. Substitution of Sn4+ for Ru4+ remains the same crystal symmetry with that of Sn‐free SrRuO3, while induces the Ru(Sn)O6 octahedral distortions. Samples with the low doping concentration (x ≤ 0.08) show a metallic behavior at high temperature, while a metal to insulator transition occurs at low temperature. On the other hand, an insulator behavior is detected for sample with x = 0.1, which follows Arrhenius‐type process in the temperature range of 80–140 K and Mott's variable range hopping model in the temperature range of 140–300 K. Further, we find that Sn4+ has a significant effect on the magnetic behavior of Sn doping in SrRuO3 where ferromagnetic transition temperature and magnetic moment decrease rapidly due to octahedral distortion and site dilution.

Perovskite as a spin current generator

We theoretically show that materials with perovskite-type crystal structures provide a platform for spin current generation, taking advantage of a mechanism requiring neither the spin-orbit coupling nor a ferromagnetic moment, but is based on spin-split band structures in certain kinds of collinear antiferromagnetic states. By investigating a multiband Hubbard model for transition metal compounds by means of the Hartree-Fock approximation and the Boltzmann transport theory, we find that a pure spin current is induced by an electric field applied to a C-type antiferromagnetic metallic phase. The spin current generation originates from a cooperative effect of spatially anisotropic electron transfer integrals owing to the GdFeO$_3$-type lattice distortion, which is ubiquitous in many perovskites, and the collinear spin configuration. We discuss our finding from the symmetry point of view, in comparison with other spin current generator candidates with collinear antiferomagnetism. We also propose several ways to detect the phenomenon in candidate perovskite materials.

Structural and Magnetic Characterizations of Ruddlesden\u2013Popper Family (Ca2-xNdxMnO4) Compound Synthesized by Ceramic Route

In this work, we were interested in the Ca2−xNdxMnO4 compounds when (0.1 ≤ x ≤ 0.4). These oxides are synthesized through the solid-state method. In this study, we investigated the evolution of the structure, the magnetic properties and the Mn3+/Mn4+ ratio with the Nd content. The morphological study shows a decrease in the size of the grain in relation to x. The X-ray diffraction reveals a transition from the tetragonal phase to the orthorhombic phase when x = 0.4. Magnetic measurements have been taken for all the compounds in the temperature range between 2 and 300 K. The temperature-dependent magnetic susceptibility shows the presence of three transitions TN, TC and TCO. A dramatic difference in magnetic susceptibility between ZFC and FC was observed below the Neel temperatures for Ca2-xNdxMnO4, which shows the onset of a ferromagnetic moment below these temperatures. This moment is caused by the Dzyaloshinskii–Moriya interaction.

Crystal symmetry for incommensurate helical and cycloidal modulations.

A classification of magnetic superspace groups compatible with the helical and cycloidal magnetic modulations is presented. Helical modulations are compatible with groups from crystal classes 1, 2, 222, 4, 422, 3, 32, 6 and 622, while cycloidal modulations are compatible with groups from crystal classes 1, 2, m and mm2. For each magnetic crystal class, the directions of the symmetry-allowed (non-modulated) net ferromagnetic moment and electric polarization are given. The proposed classification of superspace groups is tested on experimental studies of type-II multiferroics published in the literature.

Pressure-tuned spin switching in compensated GdCrO3 ferrimagnet

The effect of hydrostatic pressure on antiferromagnetic ordering of Cr spins, magnetic compensation, and exotic spin switching in the single-crystal $\mathrm{GdCr}{\mathrm{O}}_{3}$ ferrimagnet is studied. The N\'eel temperature ${T}_{\mathrm{N}}=168\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ increases under pressure with the rate of 0.42 K/kbar, and the compensation temperature ${T}_{\mathrm{comp}}=144\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ at which the canted ferromagnetic moment of Cr spins and antiparallel polarized moment of Gd spins cancel each other also increases by 0.3 K/kbar. It was found that the spin switching temperature ${T}_{\mathrm{sw}}$, at which the ferromagnetic moment is reversed, noticeably increases under pressure, and the spin switching energy required for magnetization reversal reduces significantly because of a decrease in magnetic anisotropy. Due to this mechanism, the spin switching line, described in the $T$\ensuremath{-}$H$ diagram by a certain ratio of switching energy to canted ferromagnetic moment, is shifted under pressure towards higher temperatures. Thus, switching between two opposite spin configurations in the $\mathrm{GdCr}{\mathrm{O}}_{3}$ ferrimagnet can be controlled by both applied magnetic field and external pressure.

Magnetic properties and anomalous Hall effect of Mn3Sn thin films controlled by defects and ferroelectric 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 substrate

Noncollinear antiferromagnetic Mn3Sn films have received much attention due to their potential applications in antiferromagnetic spintronic devices. In this work, single-phase polycrystalline antiferromagnetic Mn3Sn thin films were successfully prepared by magnetron sputtering. The defects in the thin films were regulated by adjusting the sputtering power. The relationship among the films structure, the anomalous Hall effect (AHE) and the defects was investigated. High defect concentration in the Mn3Sn films led to large room temperature ferromagnetic moments. The maximum saturation magnetization reached up to ~ 16 kA·m−1 (36 mμB/Mn), which was much larger than the values reported in literatures. The coercive field of 38 mT was obtained in a high-quality Mn3Sn film, which effectively reduced the flipping magnetic field. Moreover, the anomalous Hall resistance and coercive field of the Mn3Sn films prepared on the ferroelectric substrates were manipulated through an applied electric field, indicating that the piezoelectric stress has a great influence on the nonzero Berry curvature of the triangular spin structure in the antiferromagnetic materials. These results will promote the potential application of Mn3Sn in high-density and low-power antiferromagnetic spintronic devices.

Possible quadrupole order in tetragonal Ba2CdReO6 and chemical trend in the ground states of 5d 1 double perovskites

The synthesis and physical properties of the double perovskite (DP) compound Ba2CdReO6 with the 5d 1 electronic configuration are reported. Three successive phases originating from a spin–orbit-entangled J eff = 3/2 state, confirmed by a reduced effective magnetic moment of 0.72 μ B, were observed upon cooling. X-ray diffraction measurements revealed a structural transition from a high-temperature cubic structure to a low-temperature tetragonal structure at T s = 170 K, below which the J eff = 3/2 state was preserved. Magnetization, heat capacity, and thermal expansion measurements showed two more electronic transitions to a possible quadrupole ordered state at T q = 25 K and an antiferromagnetic order of dipoles with a ferromagnetic moment of ∼0.2 μ B at T m = 12 K. These properties were compared with those of the DP's sister compounds Ba2 BReO6 (B = Mg, Zn, and Ca) and the chemical trend is discussed in terms of the mean-field theory for spin–orbit-coupled 5d electrons (2010 Chen et al Phys. Rev. B 82 174440). The DP Ba2 BReO6 compounds provide a unique opportunity for a systematic investigation of symmetry breaking in the presence of multipolar degrees of freedom.

Highly Tunable Near‐Room Temperature Ferromagnetism in Cr‐Doped Layered Td‐WTe2

AbstractThe discovery of type‐II Weyl semimetal states in layered transition metal dichalcogenides Td‐WTe2 indicates great potential for novel electronic, spintronic, and quantum devices. Theoretically, the interaction between the topological states and the magnetic ordered states of Td‐WTe2 enables the modulation of Weyl semimetal states by an external magnetic field. However, currently, ferromagnetism in layered Td‐WTe2 is still elusive and rarely observed. In this research, ferromagnetic order into WTe2 using magnetic chromium (Cr) doping with a two‐step Te flux strategy is introduced. The Curie temperature (Tc) and the ferromagnetic moment are well tuned with a Cr doping concentration. The Tc of the Cr‐doped layered Td‐WTe2 could be regulated from 182 to 283 K, which is close to room temperature. The saturation magnetic moment could be changed from 2.26 to 4.20 emu g–1, which is stronger than most values reported for these materials. Most intriguingly, the Cr‐doped layered Td‐WTe2 single crystals still exhibit semimetallic behavior and they possess very large magnetoresistance with obvious Shubnikov de Haas (SdH) quantum oscillations and an anomalous Hall effect. The findings offer feasible ways to induce and tune ferromagnetic orders in layered Td‐WTe2 and thus to control its topological phase with external magnetic fields.

Functionalized magnetic composite nano/microfibres with highly oriented van der Waals CrI3 inclusions by electrospinning

This study reports on the synthesis of highly oriented chromium triiodide (CrI3) magnetic inclusions inside nano/microfibres with a polyethylene oxide matrix, prepared by the electrospinning technique. The structural, microstructural and spectroscopic analysis shows uniformly dispersed CrI3 nanosized inclusions inside the fibres, presenting a C2/m monoclinic structure at room temperature, where their c-axis is perpendicular to the fibre mat plane and the ab layers are in-plane. Analysis of the magnetic properties show that the samples have a ferromagnetic–paramagnetic phase transition at ∼55–56 K, lower than that of bulk CrI3. Noticeably, a field-driven metamagnetic transition is observed below ∼45 K, from M versus H curves, when the applied magnetic field is perpendicular to the fibre mat plane, while it is strongly reduced when the field is in-plane. This anisotropic behaviour is attributed to the field-induced changes from antiferromagnetic to ferromagnetic interlayer magnetic moment alignment along the CrI3 c-axis stacked layers. These CrI3 electrospun fibres then show an efficient cost-effective route to synthesize magnetic composite fibres with highly oriented van der Walls inclusions, for spintronic applications, taking advantage of their anisotropic 2D layered materials properties.

Quantum criticality in NdFe2Ga8 under magnetic field

We studied the magnetism in ${\mathrm{NdFe}}_{2}{\mathrm{Ga}}_{8}$ by magnetic susceptibility, specific heat, and resistivity measurements, which show ${\mathrm{Nd}}^{3+}$ ions forming one-dimensional chains along the $c$ axis. At zero field, two magnetic transitions are found at about 15 and 11 K. For field vertical to the $c$ axis, no significant effects on the magnetic orders are found. On the other hand, the two transitions are merged together at about 4 T for field parallel to the $c$ axis and completely suppressed at about 7 T. The suppression of the magnetic order results in quantum critical behaviors of the conventional three-dimensional spin-density-wave type, such as $\ensuremath{\rho}\ensuremath{\sim}{T}^{1.5}$ and $C/T\ensuremath{\sim}{T}^{\ensuremath{-}0.5}$. However, the temperature dependence of the resistivity is replaced by a ${T}^{0.5}$ behavior at very low temperatures for field larger than 3 T, which is attributed to the field-induced ferromagnetic moment. Our results suggest that there may be couplings between the antiferromagnetic quantum critical fluctuations and the field-induced ferromagnetic fluctuations.

Transformation of Co3O4 nanoparticles to CoO monitored by in situ TEM and predicted ferromagnetism at the Co3O4/CoO interface from first principles.

Nanoparticles of Co3O4 and CoO are of paramount importance because of their chemical properties propelling their applications in catalysis and battery materials, and because of their intriguing magnetic properties. Here we elucidate the transformation of Co3O4 nanoparticles to CoO into nanoscale detail by in situ heating in the transmission electron microscope (TEM), and we decipher the energetics and magnetic properties of the Co3O4/CoO interface from first principles calculations. The transformation was found to start at a temperature of 350 °C, and full conversion of all particles was achieved after heating to 400 °C for 10 minutes. The transformation progressed from the surface to the center of the nanoparticles under the formation of dislocations, while the two phases maintained a cube-on-cube orientation relationship. Various possibilities for magnetic ordering were considered in the density functional theory (DFT) calculations and a favorable Co3O4/CoO {100}/{100} interface energy of 0.38 J m−2 is predicted for the lowest-energy ordering. Remarkably, the DFT calculations revealed a substantial net ferromagnetic moment originating from the interface between the two antiferromagnetic compounds, amounting to approximately 13.9 μB nm−2. The transformation was reproduced ex situ when heating at a temperature of 400 °C in a high vacuum chamber.

Ferromagnetism of Chalcopyrite AlGaAs2:Mn Quaternary Alloys

The electronic structure and magnetic properties of chalcopyrite (CH) AlGaAs2 with dopant Mn at 3.125 and 6.25 % concentrations are investigated using first-principles calculations. The CH AlGaAs2 alloy is a p-type semiconductor with a small band-gap. The AlGaAs2:Mn shows that the ferromagnetic (FM) state is the most energetically favorable one. The Mn-doped AlGaAs2 exhibits FM and strong half-metallic ground states.The spin polarized Al(Ga,Mn)As2 state (Al-rich system) is more stable than the (Al,Mn)GaAs2 state (Ga-rich system), which has a magnetic moment of 3.82mB/Mn. The interaction between Mn-3d and As-4p states at the Fermi level dominates the other states.The states at the Fermi level are mainlyAs-4p electrons, which mediate strong interaction between the Mn-3d and As-4p states. It is noticeable that the FM ordering of dopant Mn with high magnetic moment originates from the As(4p)-Mn(3d)-As(4p) hybridization, which is attributed to the partially unfilled As-4pbands. The high FM moment of Mn is due to the double-exchange mechanism mediated by valence-band holes.

Canted antiferromagnetism in the quasi-one-dimensional iron chalcogenide BaFe2Se4

We report the synthesis and physical properties studies of quais-1D iron chalcogenide $\rm BaFe_2Se_4$ which shares the $\rm FeSe_4$ tetrahedra building motif commonly seen in the iron chalcogenide superconductors. A high-quality polycrystalline sample was achieved by solid-state reaction method and characterized by X-ray diffraction, electrical resistivity, magnetic susceptibility and neutron diffraction measurements. $\rm BaFe_2Se_4$ is a narrow gap semiconductor that magnetically orders at $\sim$ 310 K. Both neutron powder diffraction results and isothermal M-H loops suggest a canted antiferromagnetic structure where Fe sublattice are antiferromagnetically ordered along the c-axis quasi-1D chain direction, resulting in a net ferromagnetic moment in the perpendicular direction along the a-axis with tilted angle of 18.7$^\circ$ towards the b-axis.

Asymmetric Magnetization Reversal Behaviors Driven by Exchange Coupling between All-in-All-out Magnetic Domains and Domain Walls in a Eu2Ir2O7 Single Crystal

In pyrochlore iridates, nontrivial magnetic domain walls (DWs) carrying ferromagnetic (FM) moments were recently uncovered despite their bulk all-in-all-out (AIAO) antiferromagnetic (AFM) configura...

Spin and charge currents driven by the Higgs mode in high-field superconductors

The Higgs mode in superconducting materials describes slowly decaying oscillations of the order parameter amplitude. We demonstrate that in superconductors with a built-in spin-splitting field the Higgs mode is strongly coupled to the spin degrees of freedom, allowing for the generation of time-dependent spin currents. Converting such spin currents to electric signals by spin-filtering elements provides a tool for the second-harmonic generation and the electrical detection of the Higgs mode generated by the external irradiation. The nonadiabatic spin torques generated by these spin currents allow for the magnetic detection of the Higgs mode by measuring the precession of the magnetic moment in the adjacent ferromagnet. We discuss also the reciprocal effect, which is the generation of the Higgs mode by the magnetic precession. Coupling the collective modes in superconductors to light and magnetic dynamics provides an opportunity for the study of superconducting optospintronics.Received 1 July 2019Revised 23 August 2020Accepted 25 August 2020DOI:https://doi.org/10.1103/PhysRevResearch.2.033416Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasFFLOOptical conductivitySpin currentSuperconducting phase transitionPhysical SystemsFerromagnetic superconductorsHiggs bosonsMultilayer thin filmsTunnel junctionsTechniquesMethods in superconductivityCondensed Matter & Materials Physics

Strong Converse Magnetoelectric Effect in a Composite of Weakly Ferromagnetic Iron Borate and Ferroelectric Lead Zirconate Titanate

This report is on a model and experiment on the nature of mechanical-strain-mediated converse magnetoelectric (CME) effect in a composite of single-crystal iron borate, a canted antiferromagnet with a weak ferromagnetic moment, and ferroelectric lead zirconate titanate (PZT). The piezoelectric strain generated in PZT by an electric field E manifested as a shift in the quasiferromagnetic resonance (FMR) field in iron borate due to strong magnetoelastic interactions. The CME interaction strength determined from data on field shift in FMR versus E is 46--54 MHz cm/kV at 5.5--6.5 GHz. The strength of the CME is comparable to values reported for composites of ferrimagnetic oxides and PZT. A model that considers the effect of piezoelectric deformation on magnetic order parameters and magnetic resonance in iron borate is proposed for the CMEs in the composite and estimated ME coupling coefficients are in good agreement with data. The E tunability of the high-frequency AFMR mode at about 300 GHz is estimated to be on the order of 1.7 MHz kV/cm and is very small relative to the quasi-FMR mode. Composites of iron borate and ferroelectrics are very attractive for use in dual electric field and magnetic field tunable signal processing devices due to strong CME interactions and the need for a rather small bias magnetic field compared with traditional ferrimagnetic oxide based devices.

Hole-mediated ferromagnetism in a high-magnetic moment material, Gd-doped GaN

As an exotic material in spintronics, Gd-doped GaN is known as a room temperature ferromagnetic material that possesses a large magnetic moment (4000 μB per Gd ion). This paper theoretically proposes that the large magnetic moment and room temperature ferromagnetism observed in Gd-doped GaN is caused by N 2p holes based on the assumption that Ga-vacancies result from the introduction of Gd ions. This causes that the too large magnetic moment is estimated for Gd ions if only Gd ions contributed the magnetic moment.

Random fields and apparent exchange bias in the dilute Ising antiferromagnet Fe0.6Zn0.4F2

Random field induced spontaneous excess moments appear in field cooled single crystals of diluted Ising antiferromagnets. Here we report results from low temperature measurements of field cooled (including zero field) magnetic hysteresis loops parallel and perpendicular to the c-axis of a single crystal of composition Fe0.6Zn0.4F2. We find that weak static ferromagnetic excess moments attained on field cooling give rise to an apparent exchange bias of the magnetic hysteresis loops, whose magnitude is controlled by temperature and the strength and direction of the cooling field. Random field induced temporal excess moments only become observable in cooling fields larger than 1 T applied along the c-axis direction of the Fe0.6Zn0.4F2 single crystal.

Itinerant ferromagnetism in van der Waals Fe5−xGeTe2 crystals above room temperature

Two-dimensional (2D) van der Waals (vdW) magnets have recently attracted increasing attention, as they provide a novel system for exploring 2D magnetism. However, intrinsic ferromagnetism in 2D systems has almost exclusively been observed at low temperatures, limiting their technological relevance. ${\mathrm{Fe}}_{\mathrm{N}}{\mathrm{Ge}\mathrm{Te}}_{2}$ ($N=3$, 4, and 5) systems are currently becoming the most attractive 2D vdW materials due to their relatively high Curie temperatures and large saturation magnetization. However, the nature of their complex yet intriguing magnetic behaviors is still unclear, in part due to the multiple inequivalent iron sites and iron vacancies. Here, we show evolution of magnetic ordering transitions in ${\mathrm{Fe}}_{5\ensuremath{-}x}{\mathrm{Ge}\mathrm{Te}}_{2}$ with high Curie temperature and a strong saturation magnetization using photoemission electron microscopy and transport measurements. At 275 K, the ferromagnet transitions to a ferrimagnet, and below 110 K transitions to a state with glassy clusters. These are evidenced from temperature-dependent magnetic stripe domain evolution and anisotropic magnetoresistance measurements. Our findings show a clear magnetic ground state of ${\mathrm{Fe}}_{5\ensuremath{-}x}{\mathrm{Ge}\mathrm{Te}}_{2}$ at room temperature which signals that ${\mathrm{Fe}}_{5\ensuremath{-}x}{\mathrm{Ge}\mathrm{Te}}_{2}$ system is a very promising candidate for spintronic devices and provides a material design pathway to further increase the Curie temperature and saturation moments in vdW ferromagnets.