Giant magnetic moments in dilute magnetic semiconductors

The concentration dependence of the specific magnetic moment value at room temperature in dilute semiconductor titanium oxides doped with either Co or Fe has been investigated. This value was found to increase sharply at small concentrations of magnetic impurity. The magnetic moment of 22.9 μ_B per impurity atom has been revealed for TiO₂ doped with 0.15 at% Co, not yet reported in any semiconductor oxide systems. We conclude the observed giant magnetic moments are caused by the crystal lattice polarization at small impurity concentrations. The comparison with published data point to different types of the magnetization concentration dependence for various semiconductor matrixes that is probably related to the dielectric permittivity of the environment.     

Giant magnetic moments of nitrogen-doped Mn clusters and their relevance to ferromagnetism in Mn-doped GaN

Calculations based on density-functional theory show that the stability and magnetic properties of small Mn clusters can be fundamentally altered by the presence of nitrogen. Not only are their binding energies substantially enhanced, but also the coupling between the magnetic moments at Mn sites remains ferromagnetic irrespective of their size or shape. In addition, these nitrogen-doped Mn clusters carry giant magnetic moments ranging from 4mu(B) in MnN to 22mu(B) in Mn5N. It is suggested that the giant magnetic moments of MnxN clusters may play a key role in the ferromagnetism of Mn-doped GaN which exhibit a wide range (10-940 K) of Curie temperatures.     

Giant magnetic moments in ferromagnetic oxide semiconductors

Concentration dependence of the specific magnetic moment of Co-and Fe-doped titanium oxide semiconductors has been studied at room temperature. A sharp increase in the magnetic moment has been found at low concentrations of a magnetic impurity. A giant value of 22.9 μ_B per impurity atom has been detected in TiO₂ with a Co concentration of 0.15 at %, which has never been observed in oxide systems. The giant magnetic moments observed at low impurity concentration are attributed to the polarization of a crystal lattice. Comparison with the literature data indicates that the concentration dependences of magnetization are different in different oxide matrices.     

Giant magnetic moments in metals as thermodynamic fluctuations

The nucleation of giant magnetic moments in certain dilute alloys is interpreted in terms of a Landau-Ginsburg type fluctuation theory. Beyond a certain threshold value of the coupling energy of the bare impurity spin to the spin density of the host a characteristic fluctuation localized around the impurity spontaneously acquires a non-zero, autonomous value. As observed, the magnitude of the giant moment decreases with increasing impurity concentration, at least at low concentrations.     

Chiral structures and tunable magnetic moments in 3d transition metal doped Pt6 clusters

The structural, electronic, and magnetic properties of transition metal doped platinum clusters MPt6 （M=Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn） are systematically studied by using the relativistic all-electron density functional theory with the generalized gradient approximation. Most of the doped clusters show larger binding energies than the pure Pt7 cluster, which indicates that the doping of the transition metal atom can stabilize the pure platinum cluster. The results of the highest occupied molecular orbital （HOMO） lowest unoccupied molecular orbital （LUMO） gaps suggest that the doped clusters can have higher chemical activities than the pure Pt7 cluster. The magnetism calculations demonstrate that the variation range of the magnetic moments of the MPt6 clusters is from 0 μB to 7 μB, revealing that the MPt6 clusters have potential utility in designing new spintronic nanomaterials with tunable magnetic properties.     

Ground state spin local magnetic moments of deposited Fe clusters

By using the d band model within the Hartree-Fock approximation, we calculate the magnetic ground state of free and deposited Fe_N clusters (N≤30). Fe bcc and Cu fcc (100) monolayers are used as models for the deposition. A comparison between the two kinds of deposition is done. As physically expected, the more is the hybridization of a cluster with the substrate monolayer, the more is the change in its magnetic state when it is deposited. The sites of the cluster, which interact in a collective way with the substrate, are the most susceptible to change their spin local magnetic moments, when the cluster is deposited. In addition, we determined the range of the magnetic interaction of the cluster over the substrate using the obtained results.     

Non-collinear magnetic moments of seven-atom Cr, Mn and Fe clusters

The non-collinearity of magnetic moments of pentagonal bipyramid Cr₇, Mn₇ and Fe₇ clusters is discussed. The magnetic moments are calculated by the discrete variational non-collinear spin-density functional method. For the Cr₇ cluster, a coplanar magnetic arrangement appears at the large interatomic distance. With decreasing the interatomic distance, the coplanar arrangement changes to the parallel arrangement with a small absolute magnetic moment. For the Mn₇ cluster, the magnetic arrangement changes from coplanar to antiparallel with decreasing the interatomic distance. Also for the Fe₇ cluster, some coplanar magnetic moments appear at the interatomic distance of 2.23 ?. In these coplanar magnetic arrangements, the magnetic moment at the basal site of the pentagon rotates with a step of 144 degrees for the Cr₇ clusters and 72 degrees for the Mn₇ and Fe₇ clusters. Received 30 November 2000     

Chiral structures and tunable magnetic moments in 3d transition metal doped Pt₆ clusters

The structural, electronic, and magnetic properties of transition metal doped platinum clusters MPt 6 (M=Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn) are systematically studied by using the relativistic all-electron density functional theory with the generalized gradient approximation. Most of the doped clusters show larger binding energies than the pure Pt 7 cluster, which indicates that the doping of the transition metal atom can stabilize the pure platinum cluster. The results of the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gaps suggest that the doped clusters can have higher chemical activities than the pure Pt 7 cluster. The magnetism calculations demonstrate that the variation range of the magnetic moments of the MPt 6 clusters is from 0 μ B to 7 μ B , revealing that the MPt 6 clusters have potential utility in designing new spintronic nanomaterials with tunable magnetic properties.     

Giant magnetocrystalline anisotropies of 4d transition-metal monowires

The magnetocrystalline anisotropy energy (MAE) for ferromagnetic and antiferromagnetic freestanding monowires of 4d transition metals is investigated on the basis of first-principles calculations. Across the 4d series, the easy axis of the magnetization oscillates between two directions: perpendicular and along the wire axis. The largest values of the MAE occur at the end of the series. Giant values of 30-60 meV/atom can be obtained upon stretching Ru or Rh wires. Ru and Pd chains change the magnetization direction upon wire stretching, opening new perspectives in controlling the spin-dependent ballistic conductance in these structures.     

Exchange magnetic moments

Exchange magnetic moments are investigated by adopting a phenomenological approach and a field theoretical model. Their contributions are estimated for nuclei with a particle or hole outside a closed shell. They are expressed in terms of corrections of gyromagnetic factors.     

Giant light enhancement in atomic clusters

We show that the polarizing effect of the atoms in an atomic cluster can lead to full compensation of the radiative damping of excited atomic states, a change in the sign of the dispersion of the atomic polarizability, and giant light enhancement by the atomic cluster.     

Temperature-induced local magnetic moments (TILMM) in monosilicides of 3d transition metals

Features of the formation of temperature-induced local magnetic moments (TILMM) and their influence on the magnetic and thermophysical characteristics of iron, cobalt, and manganese monosilicides are investigated. The results obtained for magnetic susceptibility and specific heat measurements are discussed within the framework of spin-fluctuation theory. Temperature-concentration dependences are established for the TILMM absolute value for mutual solid solutions Fe_1–xCo_xSi and Fe_1–yMn_ySi. It is shown that for a number of the alloys studied the saturation of the TILMM absolute value does not occur, while the anomalous behavior of the polytherm of their physical properties is associated with features of the band structure.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 18–23, April, 1988.     

Giant dipole resonance in 4d photo absorption of atomic barium

We calculate the photoabsorption cross section for the 4d¹⁰ and 5p⁶ shells of atomic barium using the random phase approximation (RPAE) including relaxation. For both shells the oscillator strength goes mainly into a collective vibration of the entire shell.     

Interaction between the magnetic moments of the 3d and the 4f electrons in manganite, probed by Ga substitution

The substitution of Ga for Mn in manganite Nd_0.6Dy_0.1Sr_0.3MnO₃ with a ferromagnetic (FM) ground state has been performed to study the influence of the Mn-sublattice magnetic ordering on the magnetic rare-earth sublattice. It is found that the substitution of Mn³⁺ with Ga³⁺ ions results in a sharp decrease of T_C, reflecting the reduction of the double-exchange interactions strength J_Mn-Mn. At the same time, a depinning effect of the rare-earth magnetic moment has been observed. This behavior unambiguously proves that the exchange interaction between Mn and rare-earth ions J_Mn-R strongly influences the rare-earth magnetic ordering at temperatures below T_C and stabilizes the rare-earth magnetic ground state.     

Hyperon magnetic moments in QCD

Hyperon magnetic moments are calculated in a model-free way using the QCD sum rules. The results are in agreement with experiment.