Mn 3d States Research Articles

Structural, electronic and magnetic properties of chalcopyrite magnetic semiconductors: A first-principles study

Stimulated by recent experimental observations of room-temperature ferromagnetism of MnxCd1−xGeP2 and MnxZn1−xGeP2, we investigate the structural, electronic, and magnetic properties of this class of systems (II–Ge–V2, II=Zn, Cd, and V=As, P) as a function of Mn concentration and chemical constituents by means of first-principles density-functional- theory-based codes. Our calculations indicate that, for Mn substituting the II element, the antiferromagnetic alignment is the most stable ordering for all the systems studied. For Zn- and Cd-rich systems, the total magnetic moments per Mn atom of the ferromagnetic phase is very close to the ideal value of 5 μB, since the Mn 3d states in the minority spin channel are nearly empty; on the other hand, for Mn rich compounds, the stronger p–d hybridization lowers the total magnetic moment to about 4.4 μB.

Disorder-Induced Effects in III-V Semiconductors with Mn

The substitution of Mn in the III-V diluted magnetic semiconductors leads to a strong electron scattering on impurities. Besides the features induced in the valence band by the hybridization with the Mn d-states, also theconduction band is affected by the absence of the Mn s-states at its edge. Also the high concentration of compensating donors modifies the band structure. This is shown on the absorption coefficient e 2 (ω) of GaP doped with Mn and Se. The absorption evaluated by ab initio density functional calculations starts with a smooth tail and does not show the structure typical of III-V materials. We analyze these features and the role of the donors *on model systems using the tight-binding coherent potential approach.

ORBITAL ORDERING IN LaMnO3: CLUSTER MODEL CALCULATION OF RESONANT X-RAY SCATTERING AND X-RAY ABSORPTION AT THE MnL2,3 EDGE

We report theoretical results for resonant X-ray scattering (RXS) and linear dichroism (LD) in X-ray absorption spectra at the Mn L 2,3 edge in LaMnO 3, with special attention to the observation of orbital ordering. Calculations were performed on a ( MnO 6)10- cluster with D 4h symmetry, including the effect of intra-atomic multiplet coupling in the Mn ion. Anisotropy effects are also included, through the anisotropic Mn 3d– O 2p hybridization and crystal field parameters for Mn 3d states. The agreement between theory and experiment is good. Moreover, we show that the intensity of the peaks at the L 3 edge are strongly dependent on the Jahn–Teller distortion, while the peaks at the L 2 edge are mostly related to the orbital ordering.

An empirical study of the Mn partial density of states in icosahedral Al70Pd20Mn10

Abstract Using the line-shape analysis of the Mn 2p3/23d3d Auger transitions and by observing the Mn 3p→3d transitions in electron energy-loss spectroscopy, we have studied the local density of electronic states of the crystalline cubic and the quasicrystalline icosahedral phases of Al70Pd20Mn10. We find that, in the cubic phase the Mn 3d states coincide with the Fermi level EF, but in the quasicrystalline state the Mn 3d band is fully occupied and shifted to lower binding energies causing a significant reduction in the density of states at EF.

Electronic states of La 1− xCa xMnO 3 from photoelectron spectroscopy

The electron photoemission spectra from core-levels as well as from the valence bands of the manganese perovskites La 0.67Ca 0.33MnO 3, La 0.63Ca 0.37Mn 0.92Fe 0.08O 3 and (La 0.57Tb 0.10)Ca 0.33MnO 3 have been measured in insulating paramagnetic state at 300 K. The valence band spectra show a two-peak structure at about 3.0 and 5.7 eV below the upper edge of the valence band. Comparing the spectra with the high-resolution spectra measured at 110 eV synchrotron radiation the strong hybridisation of Mn 3d–O 2p states contributing to the valence band has been confirmed. The higher binding energy part of valence band spectrum of Tb-doped specimen shows a third feature whose physical origin is discussed. The values of the on-site Coulomb correlation energies in Mn 3d states U dd, in O 2p states U pp, the charge transfer energy Δ and the hybridisation energy between Mn 3d and O 2p states T were estimated from the Mn 2p spectra and Auger spectra analysed together with the relevant valence band spectra. Some results are compared with the 55Mn nuclear magnetic resonance data.

Charge-Carrier Localization on Mn Surface Sites in Granular LaMnO3+δ Samples

Mn K-edge X-ray absorption experiments have been carried out on the self-doped LaMnO3+δ system and compared to a (La1−xCax)MnO3 reference series. For both systems, the absorption edge and the unit cell volume vary linearly with the formal Mn(IV) content, indicating a direct correlation between the hole count in Mn 3d states and the concentration of substituents or cationic vacancies in the perovskite structure. However for the LaMnO3+δ system, a deviation from linearity occurs in the volume change at high δ values. This discontinuity is ascribed to a limit of solubility for the cationic vacancy insertion, evidenced for 30% of Mn(IV). Larger hole contents can still be measured in samples synthesized at low temperature and showing a small grain size, but these excess holes are then localized on Mn surface sites. Based on resistivity and thermopower measurements, the differences in hole doping through aliovalent substitution or vacancy insertion are discussed, highlighting the existence of a large ferromagnetic insulating composition range in the LaMnO3+δ system for 0.1≤δ≤0.15.

Magneto-spectroscopy of ordered arrays of magnetic semiconductor quantum wires

Hexagonally ordered arrays of quantum wires of the diluted magnetic semiconductor Cd 1−x Mn x S (0<x<0.2) have been obtained by incorporating the semiconductor alloy into the ordered wire-like pores of mesoporous silica hosts (MCM-41). Electron paramagnetic resonance measurements indicate that the crystalline structure of the Cd 1− x Mn x S quantum wires changes from zincblende to wurtzite with increasing x. Photoluminescence and photoluminescence excitation spectroscopy have been performed at liquid helium temperatures in external magnetic fields up to 7.5 T . The photoluminescence studies of the transitions within the half-filled Mn 3d-shell reveal the existence of at least two kinds of Mn-centres with different crystal fields. A blue shift of more than 200 meV of the absorption edge of the Cd 1− x Mn x S wires compared to that of bulk material is found due to the lateral quantum confinement in the nanowires. In addition, the p–d exchange-induced bowing of the band gap with x is enhanced in the wire structures due to the confinement-induced shift of the lowest valence band state towards the Mn 3d-states.

Electronic and magnetoresistive properties of MnAs(0001)/GaAs(111) heterostructures

Electronic band-structure calculations are carried out for the MnAs(0 0 0 1)/ GaAs(1 1 1) multilayers by using the linearized muffin-tin-orbital method within the atomic sphere approximation. The exchange splitting of Mn 3d states between spin-up and spin-down bands as well as the magnitude of local magnetic moment of Mn atoms are reduced remarkably for the Mn sites near the heterointerface compared with those in the bulk of MnAs. On the other hand, the spin-polarization at the Fermi level is enhanced for the MnAs monolayers near the heterointerface.

The valence state of Ce in electron-dopedmanganites: La0.7Ce0.3MnO3

The electronic structure of La0.7Ce0.3MnO3 (LCeMO)has been investigated by using photoemission spectroscopy. A veryweak 4f resonance is observed and the Ce 3d spectrum of LCeMO isvery similar to that of CeO2, indicating that Ce ions are farfrom being trivalent. The Mn 2p core-level spectrum of LCeMO isessentially the same as that of hole-dopedLa0.7Sr0.3MnO3, but different from that of MnO. Thelocal spin-density approximation (LSDA) electronic structure calculations for LCeMO show that the Mn3d states contribute a large peak around -2 eV and a weakstructure between -2 eV and EF, and that the O 2p statesare spread between -3 eV and -9 eV, with negligible contributionnear EF. The LSDA calculations for LCeMO and hole-dopedLa0.7Ba0.3MnO3 reveal that the calculated Mn 3ddensity of states at EF in LCeMO is larger, reflecting theeffect of electron doping with Ce ions.

Electronic states in Cu2MnX (X=Al, In, and Sn) Heusler alloy studied by XMCD and multiple scattering calculations.

X-ray magnetic circular dichroism (XMCD) has been measured at Mn and Cu K-edge in Cu2MnX (X=Al, In, and Sn) Heusler alloy. The Mn K-edge spectrum shows a dispersion-type profile and the Cu K-edge resembles the Mn spectrum, which suggests that polarization of the p unoccupied bands originates commonly in Mn 3d states. To reproduce the observed spectrum by full multiple scattering calculations. Madelung potential has been taken into account. Charge redistribution is an important factor for the electronic structure in Cu2MnX Heusler alloy.

Magnetic circular dichroism in X-ray fluorescence of Heusler alloys at threshold excitation

The results of fluorescence measurements of magnetic circular dichroism (MCD) in Mn L 2,3 X-ray emission and absorption for Heusler alloys NiMnSb and Co 2MnSb are presented. Very intense resonance Mn L 3 emission is found at the Mn 2p 3/2 threshold and attributed to a peculiarity of the threshold excitation in materials with a half-metallic character of the electronic structure. The excitation energy dependence of Mn L 2,3 X-ray emission spectra (XES) was measured at beamline ID12B at the European Synchrotron Radiation Facility (ESRF, Grenoble) using 83% circularly polarized X-rays. A very large MCD effect found in XES is attributed to strong exchange splitting of spin-up and spin-down Mn 3d states. The anomalously high ratio of L 2 emission intensity to L 3 emission intensity is found.

Electronic structure of the ferroelectromagnet YMnO 3

Using the self-consistent linear muffin-tin orbitals and atomic sphere approximation (LMTO-ASA) method, electronic structure calculations of the ferroelectromagnet YMnO 3 in the magnetic and nonmagnetic phases are performed in the local density approximation (LDA) of the density-functional theory. Total energy calculations reproduce the magnetic phase observed at low temperatures. Due to the Jahn–Teller distortion, antiferromagnetic insulating solution with a very small energy gap is also obtained. After including the strong electron–electron correlation effects in Mn 3d states by the on-site Coulomb interaction correction, the energy gap is increased to 1.1 eV and the density of states is greatly redistributed. The large component of oxygen 2p states at the top of the valence states shows that the insulator YMnO 3 has a charge-transfer character.

Temperature dependent changes of the Mn3dand4pbands nearTcin colossal magnetoresistance systems: XANES study ofLa1−xCaxMnO3

We report high-resolution X-ray Absorption Near Edge Structure (XANES) measurements at the Mn K-edge as a function of temperature, for La$_{1-x}$Ca$_x$MnO$_3$ samples, with a focus mainly on the pre-edge region. Small peaks labeled A$_1$-A$_3$ are observed which corresponds to 1s-3d dipole-transitions, made weakly allowed via a hybridization of Mn 4p states with Mn 3d states on {\it neighboring} atoms. Adjusting the parameters in an LSDA calculation to approximately match the experimental A$_1$-A$_2$ splitting yields U = 4 eV and J$_H$ = 0.7 eV. For colossal magnetoresistance samples, A$_1$ decreases with T while A$_2$ increases with T below T$_c$, which shows that the 3d bands change significant as T moves through T$_c$. There are also small changes in the shape of the main edge (1s-4p transitions).

Charge-carrier localization in the self-doped La 1− yMn 1− yO 3 system

Solution techniques allow the preparation of La 1− y Mn 1− y O 3 at low temperatures. However, the as-prepared compounds show thermodynamically induced vacancies on both cationic sites. The transport and magnetic properties strongly depend on both bulk and surface defects. In order to separate these effects, we have studied La 1− y Mn 1− y O 3 compositions by varying the vacancy content y and the grain size. The electronic structure of these phases has been investigated by means of the X-ray absorption spectroscopy at the Mn K-edge. XAS experiments have been carried out on the La 1− y Mn 1− y O 3 system as compared with the La 1− x Ca x MnO 3 reference series. For both series, the absorption edge and the unit cell volume vary linearly with the formal Mn(IV) content, resulting from a direct correlation between the hole count in Mn 3d states and the concentration of doping or of cationic vacancies in the perovskite phase. However, in the La 1− y Mn 1− y O 3 system, a deviation from this linearity occurs for vacancy contents above 30% of Mn(IV). This corresponds to a limit of solubility of the cationic vacancy in the bulk. Larger hole contents (up to 40%) may still be measured, but XANES spectra indicate that the excess holes are then trapped onto Mn sites, probably located at the surface. Despite this localization, transport measurements indicate a transition from an insulating to a metallic behavior in the low-temperature ferromagnetic regime beyond the critical concentration of 30% of Mn(IV).

Pressure Induced Quenching of Exciton Photoluminescence and its Recovery by Magnetic Field in Cadmium Telluride/Cadmium Manganese Telluride Quantum Wells

We have conducted photoluminescence (PL) measurements under hydrostatic pressures to 1.6 GPa and magnetic fields to 60T at low temperatures in a 1.0 nm thick CdTe/Cd 1-x Mn x Te (x = 0.4) single quantum well (SQW). A novel phenomenon in which an exciton PL peak from the well vanishes at 1.6 GPa and is restored by the application of a high magnetic field, was observed. We examine the possibility that the exciton energy might be dissipated to Mn 3d-states.

Interface shape and concentration distribution in crystallization from solution under microgravity

The Kerr rotation of MnBixAl0.5(0.4 less than or equal to x 0.9) thin films with and Al protective layer as a function of the Bi concentration, x, has been investigated. Compared with MnBix thin films, it is found that a large enhancement of Kerr rotation appears in the MnBixAl0.15 thin films with 0.4 less than or equal to x less than or equal to 0.7, but no enhancement of Kerr rotation appears when x is greater than 0.7. When x = 0.5, a maximum Kerr rotation of 2.75 degrees is observed at 633 nm for the MnBi0.5Al0.15 thin film, which is much larger than that of 1.56 degrees for the MnBi0.5 thin film. For the MnBixAl0.15 thin films with 0.4 less than or equal to x less than or equal to 0.7, the c lattice shrinking may result in a stronger hybridization between Bi 6p and Mn 3d states, which also should be responsible for the large enhancement of Kerr rotation. In addition, the saturation magnetization M-s is reduced from 4 x 10(5) A/m for the MnBi0.5Al0.15 thin film to 3 x 10(5) A/m for the MnBi0.5Al0.15 thin film, suggesting that some of Al may also substitute for Mn at the octahedrtal sites.

Photoemission studies of Pt 3Mn xCr 1− x

The polycrystalline Pt 3Cr 1− x Mn x ( x=0, …, 1) materials are a model system for the investigation of magnetic ordering and verification of band calculation schemes. Five samples with stoichiometries x=0, 0.3, 0.5, 0.7 and 1 were produced and analysed using X-ray diffraction and SEM. Subsequently, photoemission measurements were carried out at the synchrotron radiation source at Daresbury. The photoemission measurements indicated that there is little hybridisation between the Mn and Cr 3d states.

X-ray emission and photoelectron spectra of Pr0.5Sr0.5MnO3

Abstract The results of measurements of X-ray photoelectron (XPS), X-ray emission (XES) and X-ray absorption spectra and LSDA band structure calculations of Pr0.5Sr0.5MnO3 are presented. The excitation energy dependence of Mn L2,3 and O Kα X-ray emission spectra of Pr0.5Sr0.5MnO3 is measured using tunable synchrotron radiation. Comparing XPS and XES measurements and the LSDA band structure calculations, one concludes that the Mn 3d states are localized near the top of the valence band. Some differences in the Mn 3d-distribution in the upper part of the XPS valence band and Mn L3 XES are due to spin selection rules.

Synchrotron-radiation photoemission and inverse photoemission studies of solids

Synchrotron-radiation photoemission and inverse photoemission spectroscopies are powerful techniques to investigate occupied and unoccupied electronic states of solids. In this paper, we demonstrate that in situ measurements of ultraviolet photoemission and inverse photoemission spectra are successfully applied to studies of semiconductors. Our experimental results for Cd 1– x Mn x Te, zincblende (ZB–) and hexagonal NiAs-type (H–) MnTe, trigonal (t-) and glassy (g-) Se, and g-Ge x Se 1− x and g-As x Se 1− x are presented to discuss the Mn 3d spin-exchange splitting energy and degree of hybridization between Mn 3d and sp-band states in Cd 1− x Mn x Te, ZB– and H–MnTe, dominant source of the distinct difference of electronic structures between t- and g-Se, and percolation phenomenon in non-crystalline covalent networks in g-Ge x Se 1− x and g-As x Se 1− x , respectively.

Electronic structure of TbMn 2 and DyMn 2 single crystals

Electronic structure measurements of TbMn 2 and DyMn 2 single crystals were performed at room temperature using the X-ray photoelectron spectrometer. In the valence band of TbMn 2 a gathering of the Mn 3d states at the Fermi level was observed much stronger than that one found for DyMn 2. This structure observed in the valence band for TbMn 2 may indicate on the splitting Mn 3d band of TbMn 2 and results in a huge magnetovolume anomalies at low temperatures like for YMn 2.