Mn-Mn Interaction Research Articles

Elucidation of annealing effects on austenite–martensite and magnetic phase transitions in Mn2Ni1.6Sn0.4 ribbons synthesized from bulk alloys prepared by RF induction melting

We investigate the consequences of annealing on the structure, microstructure, magnetic, and electrical transport of Mn2Ni1.6Sn0.4 ribbons. The 40–60 μm thick ribbons were formed by melt spinning of the bulk ingot synthesized by RF induction melting. Ribbons were annealed at 600 °C for 12 hrs and the other at 800 °C for 2 hrs in vacuum. All ribbons crystallize into a cubic symmetry (space group F4¯3m). The orthorhombic phase appears as the secondary one. In ribbons annealed at 600 °C, the crystallite size decreases from ∼ 47 nm to ∼ 29 nm, and annealing at 800 °C doubles the crystallite size to ∼ 96 nm. The least amount of microstrains (17x10−4) in the as-synthesized ribbon is consistent with the occurrence of the superlattice peaks (111) and (200). Lower intensities of the superlattice peaks in 600 °C and 800 °C ribbons are consistent with higher microstrains (25x10−4 and 24x10−4). Hence, a higher degree of Ni-Mn ordering improves magnetic properties in annealed samples. The as-synthesized ribbon has an austenite-phase Curie temperature of TCA∼303K, which enhances to TCA∼320K and TCA∼310K after annealing at 600 °C and 800 °C. The ribbon annealed at 600 °C has the highest saturation moment. All the ribbons show the exchange-bias (EB) effect, and the most pronounced effect is seen in the 800 °C annealed ribbon. Microstructure uniformization and relative strengths of the Ni-Mn and Mn-Mn interactions improve the magnetics. Near TC, MT=M0TC-Tβ is satisfied (β = 0.31, 0.36, and 0.37, for as-synthesized, 600 °C and 800 °C annealed ribbons). The low-temperature spontaneous magnetization obeys the Bloch law MT=M01-AT32, with a deviation in 600 °C annealed ribbon due to spin freezing. The ρ-T has been fitted in the different temperature ranges using the various combinations in ρT=ρ0+AphT+BsdTα. At T < 85 K, the resistivity of the as-synthesized ribbon follows ρT=ρ0+BsdTα, with α≈1.47, while for the 600 °C annealed ribbon, α≈1.49. The exponent α∼1.5 supports the existence of the spin glass state in the lower temperature region of as-synthesized and 600 °C annealed ribbons. In the high-temperature range, the linear ρ-T behavior is described by ρT=ρ0+AphT and consistent with the electron–phonon scattering.

The influence of substrate orientation on the magnetic behavior of nearly-stoichiometric Mn5Ge3 thin films: DFT calculations and experimental analysis

The Mn5Ge3 exhibits a wide range of fascinating properties such as high spin polarization up to 42 %, large spin diffusion lengths, near-room Curie temperature, and possible integration with Ge, GaAs, and Si substrates. The influence of substrate orientation on magnetic behavior has been investigated. The thin films studied present an in-plane magnetic reversal which is isotropic in samples grown on GaAs(111) and anisotropic in samples grown on GaAs(001). Another difference observed is a linear trend to saturation on the out-of-plane hysteresis loop in samples grown on GaAs(111), comparatively to samples grown on GaAs(001). To better understand this scenario, Density Functional Theory (DFT) calculations were conducted. The results indicate a ferromagnetic metallic ground state with properties that are consistent with the experimental results. The projected densities of states indicate that the main responsible for the magnetic moment observed in the Mn5Ge3 is the Mn-Mn interaction. The magnetic field distribution isosurfaces obtained from the DFT calculations offer a satisfactory explanation of the magnetic reversal experimentally observed, especially the in-plane magnetic behavior in samples grown on both GaAs(111) and GaAs(001) substrates. This work provides a theoretical-experimental approach that allows a deeper understanding of the magnetic anisotropy behavior under the influence of the crystallographic orientation of the substrate observed in nearly-stoichiometric Mn5Ge3 thin films, which is a good candidate for rare-earth free magnet in spintronic applications.

Critical behavior in the ferromagnet

High-Curie-temperature ferromagnets are promising candidates for designing new spintronic devices. Here we have successfully synthesized the single crystal of the itinerant ferromagnet Mn5Ge3 using flux method. Its critical properties were investigated by means of bulk dc magnetization at the boundary of the paramagnetic (PM) and ferromagnetic (FM) phase to determine intrinsic magnetic interactions. Critical exponents with a critical temperature K and with K are acquired by the modified Arrott plot, whereas is deduced by a critical isotherm analysis at K. The self-consistency and reliability of these critical exponents are verified by the Widom scaling law and the scaling equations. Further analysis reveals that the spin interaction in Mn5Ge3 exhibits three-dimensional Ising-like behavior. The magnetic exchange interaction is found to decay as , meaning that the spin interactions exceed the nearest neighbors, which may be related to the different Mn-Mn interactions with inequal exchange strengths.

Magnetic properties of the off-stoichiometric Heusler alloys Rh2Mn1+xSn1-x

We report the results of experimental investigation of the crystal structure, magnetization and 119Sn Mössbauer spectroscopy of Rh2Mn1+xSn1-x (0 ≤ x ≤ 0.6). The samples crystallize in the cubic L21-type structure for 0 ≤ x ≤ 0.4 and the cubic B2-type structure for x = 0.5 and 0.6. X-ray diffraction patterns with the samples with 0 ≤ x ≤ 0.4 indicate that the excess Mn atoms occupy the Sn sites. The samples with 0 ≤ x ≤ 0.4 exhibit the typical ferromagnetic behavior. The magnetic moment at 5 K of 4.27 μB/f.u. for x = 0 (Rh2MnSn) initially increases with increasing x and saturates for x ≥ 0.2. On the other hand, the Curie temperature for 0 ≤ x ≤ 0.4 decreases with increasing x. It is presumed that both samples with x = 0.5 and 0.6 are in the heterogeneous magnetic state. The 119Sn Mössbauer spectroscopy measurements showed that the hyperfine field at 90 K for 0 ≤ x ≤ 0.6 increases with increasing x. The concentration dependence of the magnetic moment and the Curie temperature for Rh2Mn1+xSn1-x (0 ≤ x ≤ 0.6) are discussed qualitatively based on the Mn-Rh and Mn-Mn interactions in the crystal.

Multiple magnetic transitions induced by Mn-doping in orthochromite HoCrO3

It has been established that both hybridization with magnetic rare earth cation and crystal field originating from structural anisotropy can affect the spin orientation of magnetic transition metal perovskite. In this work, we have systematically studied the crystal structure, magnetization, and magnetic structure of Mn-doped rare earth orthochromites HoCr1−xMnxO3 (x = 0–0.85) by means of X-ray diffraction, magnetometry, and neutron powder diffraction. With increasing Jahn–Teller active Mn3+-substitution for Cr3+, the crystallographic distortion is gradually enhanced and causes a systematic evolution of magnetism. With doping, the Cr(Mn) ordering temperature is gradually suppressed, and multiple magnetic configurations Γ2, Γ1, and Γ4 phases appear consecutively. The rich transition phenomena are ascribed to a competition between increased structural anisotropy and weakened Ho-Cr(Mn) hybridization with doping. In a low doping regime with x = 0.1–0.5, Γ2 phase is predominant in low temperature, and a magnetization reversal is observed, reflecting the opposite sign of Cr-Mn DMI coefficient with respect to the Cr-Cr and Mn-Mn interaction. In the high doping range with x = 0.6–0.8, the long-range order of Cr(Mn) sublattice is gradually suppressed while a short-range order becomes dominant. For x = 0.85, a magnetic structure resembling o-HoMnO3 is observed.

The Effects of Mono- and Bivalent Linear Alkyl Interlayer Spacers on the Photobehavior of Mn(II)-Based Perovskites.

Mn(II)-based perovskite materials are being intensively explored for lighting applications; understanding the role of ligands regarding their photobehavior is fundamental for their development. Herein, we report on two Mn (II) bromide perovskites using monovalent (perovskite 1, P1) and bivalent (perovskite 2, P2) alkyl interlayer spacers. The perovskites were characterized with powder X-ray diffraction (PXRD), electron spin paramagnetic resonance (EPR), steady-state, and time-resolved emission spectroscopy. The EPR experiments suggest octahedral coordination in P1 and tetrahedral coordination for P2, while the PXRD results demonstrate the presence of a hydrated phase in P2 when exposed to ambient conditions. P1 exhibits an orange-red emission, while P2 shows a green photoluminescence, as a result of the different types of coordination of Mn(II) ions. Furthermore, the P2 photoluminescence quantum yield (26%) is significantly higher than that of P1 (3.6 %), which we explain in terms of different electron-phonon couplings and Mn-Mn interactions. The encapsulation of both perovskites into a PMMA film largely increases their stability against moisture, being more than 1000 h for P2. Upon increasing the temperature, the emission intensity of both perovskites decreases without a significant shift in the emission spectrum, which is explained in terms of an increase in the electron-phonon interactions. The photoluminescence decays fit two components in the microsecond regime-the shortest lifetime for hydrated phases and the longest one for non-hydrated phases. Our findings provide insights into the effects of linear mono- and bivalent organic interlayer spacer cations on the photophysics of these kinds of Mn (II)-based perovskites. The results will help in better designs of Mn(II)-perovskites, to increase their lighting performance.

Spin and charge density waves in quasi-one-dimensional KMn6Bi5

AMn6Bi5 materials (A = Na, K, Rb and Cs) consisting of unique Mn-cluster chains emerge as a new family of superconductors with the suppression of their antiferromagnetic (AFM) order under high pressures. Here, we report transverse incommensurate spin density waves (SDWs) for the Mn atoms with a propagating direction along the chain axes as a ground state for KMn6Bi5 by single crystal neutron diffraction. The SDWs have a refined amplitude of ~2.46 Bohr magnetons for the Mn atoms in the pentagons and ~0.29 Bohr magnetons with a large standard deviation for Mn atoms in the center between the pentagons. AFM dominate both the nearest-neighbor Mn-Mn interactions within the pentagon and next-nearest-neighbor Mn-Mn interactions out of the pentagon (along the propagating wave). The SDWs exhibit both local and itinerant characteristics probably formed by a cooperative interaction between local magnetic exchange and conduction electrons. A significant magnetoelastic effect during the AFM transition, especially along the chain direction, has been demonstrated by temperature-dependent x-ray powder diffraction. Single crystal x-ray diffraction below the AFM transition revealed satellite peaks originating from charge density waves along the chain direction with a q-vector twice as large as the SDW one, pointing to a strong real space coupling between them. Our work not only manifests a fascinating interplay among spin, charge, lattice and one dimensionality to trigger intertwined orders in KMn6Bi5 but also provides important piece of information for the magnetic structure of the parent compound to understand the mechanism of superconductivity in this new family.

Enhanced Property Tunability of Doubly Doped Semiconductor Nanomaterials Using the Cluster Seed Method

Semiconductor Quantum Dots (QDs) have great potential in applications for renewable energy generation due to their size-tunable redox potentials. They may be prepared with different morphologies and coated to create complex heterostructures. Doping of semiconductor nanomaterials is another mechanism to realize property tunability, and doped QDs are playing an increasing role in green energy generation applications. In 2013 our group reported a method to create a batch of doped quantum dots where each particle was embedded with the same number of guest ions, thus circumventing Poisson statistics. This was accomplished by nucleating the QD around an organometallic seed cluster that contains guest ions. As a result, each QD has the same number of dopants, which eliminates problems due to inhomogeneity of the guest ion stoichiometry. These materials were studied using time-resolved X-ray absorption spectroscopy, which allows us to characterize the electronic and coordination structure in both the ground and excited states.Current research reveals the potential to doubly dope semiconductors using cluster seeding, and that the originating organometallic structure may be represented in the final material product. To this end, ZnCdSe nanowires were prepared in the presence of (MnTe)4 cluster seeds. The results reveal that Mn(2+) has been successfully incorporated into the host matrix, while temperature dependent optical measurements suggest significantly enhanced semiconductor exciton-magnetic dopant interactions in materials prepared by cluster seeding compared to doped control samples. This could be due to ferromagnetic Mn-Mn interactions in the host resulting from enhanced exchange coupling mediated by highly spin-orbit coupled tellurium bridging. Consequently, cluster seeding may be used to "dope the dopants", affording a heretofore unrealized method for developing designer materials with enhanced electronic and optical properties. Figure 1

Raman spectroscopy investigation of vibrational mode of Sb2-xMnxTe3 nanocrystals in host glass

Vibrational modes property variations of diluted magnetic semiconductor nanocrystals of Sb2xMnxTe3 grown in a glass host system were investigated. Transmission electron microscopy images and energy dispersive X-ray analysis confirm the size, interplanar distance and composition of these NCs. Electronic paramagnetic resonance spectra confirm the incorporation of manganese ions in the Sb2Te3 crystal lattice due to the six absorption lines. Moreover, changes in Mn-Mn interactions are observed as xMn-concentration increases. The Raman- and IR-active vibrational modes of quintuple layer changes of the Sb2-xMnxTe3 NCs give strong evidence of the incorporation of Mn2+ ions in Sb2Te3 NCs.

Highly efficient emission in lead-free inorganic vacancy-ordered Sb-Bi-alloyed halide quadruple perovskites

Lead-free vacancy-ordered quadruple perovskites have received extensive attention in optoelectronic applications. We study the optical properties and charge-carrier dynamics of Cs4Mn(Bi1-xSbx)2Cl12 (0 ≤ x ≤ 1) quadruple perovskite single crystals (SCs), which exhibit excellent stability and Mn2+-based photoluminescence (PL) emission. The ratio of Bi:Sb has a great influence on PL intensity. As the Bi3+ content increases, the PL quantum yield (PLQY) shows a monotonically increasing trend and enhances by more than 40 times, attributed to larger energy difference between conduction band minimum and 4T1 state of Mn2+ ions, weaker Mn-Mn coupling interaction due to longer Mn···Mn distance and smaller Jahn-Teller distortion, and lower carrier-phonon coupling. Moreover, Cs4Mn(Bi1-xSbx)2Cl12 nanocrystals were synthesized through top-down ultrasonic crushing method. The PL quenching of Cs4MnBi2Cl12 nanocrystals compared to corresponding SCs arises from surface defect trapping. Our work provides an in-depth understanding of Mn2+-based PL mechanism.

Colloidal Manganese-Doped ZnS Nanoplatelets and Their Optical Properties

Manganese (Mn)-doped ZnS nanocrystals (NCs) have been extensively explored for optical applications with the advantages of low toxicity, large Stokes shifts, and enhanced thermal and environmental stability. Although numerous studies on Mn-doped ZnS dots, rods, and wires have been reported, the literature related to Mn-doped ZnS nanoplatelets (ZnS:Mn NPLs) is scarce. Here, we present the first example of direct doping of Mn2+ ions into ZnS NPLs via the nucleation-doping strategy. The resulting ZnS:Mn NPLs exhibit Mn luminescence, indicative for successful doping of the host ZnS NPLs with Mn2+ ions. The energy transfer from the ZnS NPLs to the Mn2+ ions was observed by employing spectroscopic methods. Furthermore, the impact of the Mn concentration on the optical properties of ZnS:Mn NPLs was systematically investigated. As a result of Mn-Mn interaction, tunable Mn emission and shortened photoluminescence (PL) lifetime decay were observed and rationalized by means of electron paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS). Finally, we show that the initially low dopant PL quantum yield (QY) of ZnS:Mn NPLs can be dramatically enhanced by passivating the surface trap states of the samples. The presented synthetic strategy of ZnS:Mn NPLs opens a new way to synthesize further doped systems of two-dimensional (2D) NPLs.

Equilibrium solute segregation to matrix- θ′ precipitate interfaces in Al-Cu alloys from first principles

Particular combinations of solute atoms segregated to the interface of the Al and ${\ensuremath{\theta}}^{\ensuremath{'}}\text{\ensuremath{-}}{\mathrm{Al}}_{2}\mathrm{Cu}$ in Al-Cu alloys can help stabilize ${\ensuremath{\theta}}^{\ensuremath{'}}$ precipitates at high temperatures. Stabilization of such precipitates is determined by a combination of thermodynamics (including driving forces for coarsening and transformation and solute segregation tendencies) and kinetic effects (including solute diffusion and interfacial mobility in the presence of interfacial solute segregation). For some alloys such as recent Al-Cu-based alloys, multiple solutes segregate in significant quantities to interfaces, and solute-solute interactions at the interface are important, with multiple types of solutes competing for similar interfacial sites. To treat this situation, we develop and apply a statistical mechanics approach to calculate the temperature-dependent equilibrium solute atoms distribution near the coherent and semicoherent interfaces between the Al matrix and the ${\ensuremath{\theta}}^{\ensuremath{'}}\text{\ensuremath{-}}{\mathrm{Al}}_{2}\mathrm{Cu}$ precipitates. The developed approach is applied to the investigation of Si, Mn, and Zr segregation at the interface, as particular combinations of these elements affect the thermal stability of the ${\ensuremath{\theta}}^{\ensuremath{'}}$ precipitates. We demonstrate that because Si and Mn atoms segregate on the same semicoherent interface, the presence of Si reduces the concentration of Mn solutes at the interface. Si atoms preferably occupy the first layer of the interface and compete with Mn atoms for one type of particular sites in the layer. Mn atoms preferably occupy the second layer of the semicoherent interface, and the Mn-Mn interaction plays an important role in their distribution. Zr atoms mostly segregate on one of the two nonequivalent sites of the second layer of the coherent interface. Due to symmetry properties of the coherent interface, the calculations show that the segregation Zr of atoms to this interface will likely lead to the formation of ${\mathrm{L}1}_{2}$ ordered ${\mathrm{Al}}_{3}\mathrm{Zr}$ layer.

Thermal expansion of pyrolusite, β-MnO2; a synchrotron X-ray diffraction study

High resolution synchrotron X-ray powder diffraction (S-XRD) methods have been used to study the temperature dependence of the structure of β-MnO2 between room temperature and 400 °C. Rietveld analysis of the S-XRD data provided accurate and precise until cell parameters from which the thermal expansion coefficients (TEC) were determined, αa = 7.8 × 10−6 K−1 and αc =7.2 × 10−6 K−1. The difference in the anisotropy in the TEC and the temperature dependence of the distortion of MnO6 and TiO2 suggests MnMn interactions across the shared edge are significant.

Magnetic structures and magnetic phase transitions in RMn2Si2

Magnetic properties of the LaMn2Si2 and La0.6R0.4Mn2Si2 (R = Sm, Tb, Gd) compounds with layered ThCr2Si2-type structure have been studied using quasi-single-crystalline and polycrystalline samples. Substitution of the R atoms for La decreases the interatomic distances and changes the ordering of the Mn sublattice from ferromagnetic to antiferromagnetic. Magnetic structure of the substituted compounds has been found to depend on the anisotropy of R ions. The Sm moments are oriented in the basal plane and weakly coupled with the Mn sublattice. For R = Tb, frustrations prevent the formation of long-range magnetic ordering in Tb sublattice. For the system with Gd, the antiferromagnetic Mn-Mn and Gd-Mn interactions lead to a change of magnetic anisotropy from the easy-axis to the easy-plane type.

Designing a New Ni-Mn-Sn Ferromagnetic Shape Memory Alloy with Excellent Performance by Cu Addition

Both magnetic-field-induced reverse martensitic transformation (MFIRMT) and a high working temperature are crucial for the application of Ni-Mn-Sn magnetic shape memory alloys. Here, by first-principles calculations, we demonstrate that the substitution of Cu for Sn is effective not only in enhancing the MFIRMT but also in increasing martensitic transformation, which is advantageous for its application. Large magnetization difference (ΔM) in Ni-Mn-Sn alloy is achieved by Cu doping, which arises from the enhancement of magnetization of austenite due to the change of Mn-Mn interaction from anti-ferromagnetism to ferromagnetism. This directly leads to the enhancement of MFIRMT. Meanwhile, the martensitic transformation shifts to higher temperature, owing to the energy difference between the austenite L21 structure and the tetragonal martensite L10 structure increases by Cu doping. The results provide the theoretical data and the direction for developing a high temperature magnetic-field-induced shape memory alloy with large ΔM in the Ni-Mn-Sn Heusler alloy system.

Electronic structure and magnetism of Ge(Sn)TMXTe1−X (TM = V, Cr, Mn): A first principles study

This work presents the results of first principles calculations of the electronic and magnetic properties of the compound SnTe and GeTe in zinc blende (ZB) and rock salt (RS) structures, doped with 3d transition metal V, Cr, and Mn. The present study, initiated from the viewpoint of potential application in spintronics, is motivated by our earlier work involving these two compounds, where the doping was limited to the Sn and Ge sublattices. In view of some discrepancies between our calculated results and the available experimental data, in this work we have examined the effect of the Te-sublattice doping. The case of Mn-doping, where the previous results of calculations seemed to differ most from the experimentally available data, is examined further by looking at the effect of Mn atoms partially occupying interstitial sites as well. From the standpoint of potential application in spintronics, we look for half-metallic (HM) states and tabulate their properties in both rock salt and zinc blende structures. ZB structure is found to be more conducive to HM state in general. Among the binary compounds we identify several HM candidates: VGe, VSn, MnGe, MnSn and MnTe at their equilibrium volumes and all in ZB structure. Estimates of the Curie temperature for the ferromagnetic compounds including the half-metals are presented. It is shown that despite the ferromagnetic (FM) nature of the Mn-Mn interaction for the Te-doped case, a simultaneous doping of both Ge(Sn)- and Te-sublattice with Mn atoms would leave the material predominantly antiferromagnetic (AFM).

Structural evolution and magnetic properties of L10-type Mn54.5Al45.5-xGax (x = 0.0, 15.0, 25.0, 35.0, 45.5) phase

The intermetallic compounds Mn54.5Al45.5-xGax (x = 0.0, 15.0, 25.0, 35.0, 45.5) with L10 structure were prepared by melt-spinning and annealing. The structural and magnetic properties were investigated by means of X-ray diffraction, neutron powder diffraction and magnetic measurement. Al and Ga atoms are found to occupy both the 1a (0, 0, 0) and 1d (1/2, 1/2, 1/2) sites and show a preference occupation for the 1d site. It was found that the lattice parameter a slightly decreases, while c abnormally increases with the increase of Ga content x, which can be attributed to the fact that the Ga atom located at the 1d sites is larger than that of Al. The mass magnetization decreases from 134 emu/g to 91 emu/g at 5 K as x increases from 0.0 to 45.5 due to higher density of the alloys with Ga in comparison to the alloys with Al. A coercivity (iHc) value of 3.67 kOe and the maximum energy product (BH)max of 2.05 MGOe were obtained for Mn54.5Al30.5Ga15 sample. All the L10 samples show a Curie temperature (Tc) well above room temperature and the value of Tc decreases almost linearly from 644 K for Mn54.5Al45.5 to 578 K for Mn54.5Ga45.5 due to the decrease of ferromagnetic Mn-Mn interaction in the a-b plane. The observed magnetic properties are in accordance with the competing ferromagnetic interactions between Mn moments at the regular 1a site and antiferromagnetic coupling with the excess Mn atoms occupying the Ga (1d) site.

Magnetism of ordered and disorderedNi2MnAlfull Heusler compounds

Based on ab initio calculations and Monte Carlo simulations, we present a systematic study of the magnetic ground state and finite temperature magnetism of ordered and disordered ${\mathrm{Ni}}_{2}\mathrm{MnAl}$ full Heusler compounds. By increasing the degree of the long-range chemical disorder between the Mn and Al sublattices, the magnetic order progressively changes from the ferromagnetic state in the ordered $L{2}_{1}$ phase toward a fully compensated antiferromagnetic state in the disordered $B2$ phase and we also conclude that the Ni atoms exhibit induced moments. We determine the Mn-Mn interactions by using the magnetic force theorem and find dominating, but rather weak ferromagnetic couplings in the ordered $L{2}_{1}$ phase. We used a recently proposed renormalization technique to include the weak Ni moments into the spin model, which indeed remarkably increased the nearest-neighbor Mn-Mn interaction. In accordance with the total energy calculations, in the disordered compounds, strong antiferromagnetic site-antisite Mn-Mn interactions appear. Determining the spin-spin correlation functions from Monte Carlo simulations, we conclude that above the transition temperature, short-range antiferromagnetic correlations prevail between the Mn atoms. In view of the potential application of disordered ${\mathrm{Ni}}_{2}\mathrm{MnAl}$ as a room temperature antiferromagnet, we calculate the magnetic anisotropy energies of tetragonally distorted samples in the $B2$ phase and find that they are smaller by two orders in magnitude than in the frustrated antiferromagnet ${\mathrm{IrMn}}_{3}$.

Magnetoresistance quantum oscillations in a magnetic two-dimensional electron gas

Magneto-transport measurements of Shubnikov-de Haas (SdH) oscillations have been performed on two-dimensional electron gases (2DEGs) confined in CdTe and CdMnTe quantum wells. The quantum oscillations in CdMnTe, where the 2DEG interacts with magnetic Mn ions, can be described by incorporating the electron-Mn exchange interaction into the traditional Lifshitz-Kosevich formalism. The modified spin splitting leads to characteristic beating pattern in the SdH oscillations, the study of which indicates the formation of Mn clusters resulting in direct anti-ferromagnetic Mn-Mn interaction. The Landau level broadening in this system shows a peculiar decrease with increasing temperature, which could be related to statistical fluctuations of the Mn concentration.

Origin of the magnetostructural coupling inFeMnP0.75Si0.25

The strong coupling between the crystal structure and magnetic state (ferromagnetic or helical antiferromagnetic) of FeMnP0.75Si0.25 is investigated using density functional theory in combination with atomistic spin dynamics. We find many competing energy minima for drastically different ferromagnetic and noncollinear magnetic configurations. We also find that the appearance of a helical spin-spiral magnetic structure at finite temperature is strongly related to one of the crystal structures reported for this material. Shorter Fe-Fe distances are found to lead to a destabilized ferromagnetic coupling, while out-of-plane Mn-Mn exchange interactions become negative with the shortening of the interatomic distances along the c axis, implying an antiferromagnetic coupling for the nearest-neighbor Mn-Mn interactions. The impact of the local dynamical correlations is also discussed.