Magnetic Moments Of Mn Ions Research Articles

Investigation of pressure effects on [formula omitted

In the present work, the pressure effects on the electronic and magnetic properties of Mn x Ge 1 - x semiconductor have been investigated. The obtained results show that the lattice constant of Mn x Ge 1 - x increases with the Mn concentration increase. The magnetic moments of Mn ions decrease with increasing pressure. The interactions between Mn ions is a Ruderman–Kittel–Kasuya–Yosida like one over the whole pressure range applied. The role of the pressure actually increases the intensity of the interactions, and consequently the Curie temperature of Mn-doped Ge system increases with the pressure increase.

Emission properties of InGaAs/GaAs heterostructures with δ⟨Mn⟩-doped barrier

Light-emitting device heterostructures with a δ⟨Mn⟩-doped layer inserted between the Schottky contact and near-surface InGaAs/GaAs quantum well (QW) have been fabricated. The δ⟨Mn⟩-doped layer facilitates hole tunnelling from the Schottky contact to the QW and impedes that of QW electrons in the opposite direction. It leads to a highly enhanced electroluminescence signal from the InGaAs QW. An effective p–d exchange interaction of holes with magnetic moments of Mn ions is found to strongly enhance the effective hole g-factor and the circular polarization of the low (∼2 K) temperature emission up to 20% in magnetic fields of 1–2 T.

Hexagonal frustrated RMnO3 manganites (R = Y, Lu) under high pressure

The crystalline and magnetic structures of YMnO3 and LuMnO3 hexagonal manganites under pressures of 0–6 GPa and in the temperature range 10–295 K have been investigated by neutron diffraction. Application of pressure leads to a significant decrease in the ordered magnetic moment of Mn ions (at T = 10 K) from 3.27 (0 GPa) to 1.52 μB (5 GPa) for YMnO3 and from 2.48 (0 GPa) to 1.98 μB (6 GPa) for LuMnO3. Under high pressures, spin reorientation of Mn magnetic moments and a change in the symmetry of the antiferromagnetic structure are observed in YMnO3. The relationship between the triangular lattice distortion parameter and the symmetry of the triangular antiferromagnetic state of RMnO3 hexagonal manganites is discussed.

High-pressure effect on the crystal and magnetic structure of LuMnO3: Correlation between a distortion of the triangular lattice and the symmetry of the magnetic state in hexagonal frustrated manganites

The effect of a high pressure (up to 6 GPa) on the crystal and magnetic structure of the hexagonal manganite LuMnO3 is studied by neutron diffraction in the temperature range 10–295 K. It is found that, as the pressure increases, the ordered magnetic moment of Mn ions at T = 10 K decreases noticeably from 2.48 (0 GPa) to 1.98 μB (6 GPa). This decrease is due to an enhancement of the geometrical frustration effects on the triangular lattice. At the same time, the symmetry of the triangular antiferromagnetic state (the irreducible representation Γ2) remains unchanged. A correlation is revealed between the distortion parameter of the triangular lattice formed by Mn ions and the symmetry of the antiferromagnetic state of hexagonal manganites RMnO3. Based on this correlation, a generalized magnetic phase diagram of these compounds is constructed. The obtained phase diagram provides an explanation for the changes observed in the magnetic state of hexagonal manganites caused by high pressure and chemical substitution.

High-pressure effect on the crystal and magnetic structures of the frustrated antiferromagnet YMnO3

The high-pressure (to 5 GPa) effect on the crystal and magnetic structures of the hexagonal manganite YMnO3 is studied by neutron diffraction in the temperature range 10–295 K. A spin-liquid state due to magnetic frustration on the triangular lattice formed by Mn ions is observed in this compound at normal pressure and T > TN = 70 K, and an ordered triangular antiferromagnetic state with the symmetry of the irreducible representation Γ1 arises at T < TN. The high-pressure effect leads to a spin reorientation of Mn magnetic moments and a change in the symmetry of the antiferromagnetic structure, which can be described by a combination of the irreducible representations Γ1 and Γ2. In addition, it is observed that the ordered magnetic moment of Mn ions decreases from 3.27 μB (5 GPa) to 1.52 μB (5 GPa) at T = 10 K and diffuse scattering is enhanced at temperatures close to TN. These effects can be explained within the model of the coexistence of the ordered antiferromagnetic phase and the spin-liquid state, whose volume fraction increases with pressure due to the enhancement of frustration effects.

Crystal and magnetic structure of the Sm0.55Sr0.45MnO3 and (Nd0.545Tb0.455)0.55Sr0.45MnO3 manganites

Neutron diffraction data are presented for the 152Sm0.55Sr0.45MnO3 (SSM) and (Nd0.545Tb0.455)0.55Sr0.45MnO3 (NTSM) manganites. The Nd and Tb contents in the latter composition are such that the average radius of the A cation 〈rA〉 in these two compounds is the same. The difference in local tolerance factor fluctuations was about 10%. It was found that replacement of a rare-earth cation with leaving 〈rA〉 unchanged has practically no effect on the structural and transport properties; indeed, both compounds are metals at low temperatures, have the same crystal structure from liquid-helium to room temperature, and exhibit the same pattern of structural distortions at the onset of magnetic ordering. Magnetic moments of Mn ions in both compositions are ferromagnetically ordered at low temperatures, with TC=122 and 90 K for the SSM and NTSM, respectively. Below 80 K, the rare-earth cation moments in NTSM undergo additional ordering. In contrast to compositions that are close in Sr concentration (xSr=0.4, 0.5), which feature a phase-separated state with a mixture of the ferromagnetic metallic and antiferromagnetic insulator phases, the ground state of both studied compositions with xSr=0.45 is uniformly ferromagnetic and metallic.

Interaction of charge carriers with the localized magnetic moments of manganese atoms in p-GaInAsSb/p-InAs:Mn heterostructures

Transport properties of p-Ga1−xInxAsySb1−y/p-InAs:Mn heterostructures with undoped layers of solid solutions similar in composition to GaSb (x≲0.22) grown by liquid-phase epitaxy on substrates with a Mn concentration of (5–7)×1018 cm−3 are studied. It is ascertained that there is an electron channel at the interface (from the InAs side). The anomalous Hall effect and negative magnetoresistance are observed at relatively high temperatures (77–200) K. These phenomena can be attributed to the s-d-exchange interaction between Mn ions of the substrate and s electrons of the two-dimensional channel. The effective magnetic moment of Mn ions was evaluated as μ=200µB at T=77 K.

Jahn–Teller distortion and cluster-glass like behavior in La 0.875Ca 0.125MnO 3

Neutron diffraction and magnetization measurements were carried out on both powder and single crystal samples of La 0.875Ca 0.125MnO 3. At room temperature (RT), this sample is paramagnetic and single phase, with crystallographic symmetry Pnma (the longest axis is b-axis). Neutron powder diffraction shows that the average magnetic moment of Mn ions is 3.0 (1) μ B/Mn at 10 K, which is significantly less than an averaged moment estimated from the ratio of Mn 3+/Mn 4+ which amounts to 3.875 μ B for 12.5% Mn 4+, an indication of spin canting. The crystal structure is characterized by the ordering of two e g orbitals, being evidenced by the anomalous change of Mn–O bond lengths which starts from 100 K with decreasing temperature. Neutron diffraction measurement was carried out at 8 K and RT. Diffuse scattering at around 1/2 0 1/2 point was observed at 8 K but disappeared in the paramagnetic region.

Modulated magnetic orderingin the Cu-doped pseudoperovskite systemCaCuxMn3-xMn4O12

The crystal and magnetic structures of theCaCuxMn3-xMn4O12 compounds with x = 0.3 and0.7 were investigated by means of x-ray and neutron powderdiffraction. The crystal structure parameters of the x = 0.3compound at 60 K have been refined within the trigonal spacegroup R3̄. The magnetic moments of Mn ions in thex = 0.3 sample become ordered below 40 K. The magneticordering is modulated with a propagation vector (0,0,κ).A model of the magnetic structure which is in agreement with theexperimental data is proposed along with an estimation of thetemperature dependence of the magnetic moment value. Themagnetic ordering has a reduced correlation length of about250 Å. The x = 0.7 compound does not show any long-rangemagnetic ordering down to 1.5 K.

Magnetoluminescence of Zn(Mn)Se/Be(Mn)Te semimagnetic heterostructures with a type-II band alignment

Zn(Mn)Se/Be(Mn)Te semiconductor heterostructures with a type-II band alignment have been fabricated by molecular-beam epitaxy. Giant Zeeman splitting of the band states, caused by their interaction with the localized magnetic moments of Mn ions, has been observed for the spatially direct and indirect optical transitions. Strong p–d exchange interaction for the valence band states in (Be,Mn)Te has been demonstrated experimentally.

Ground state properties of a high-spin Mn12O12 molecule in an organic compound

The electronic structure and the magnetism of a Mn12O12 molecule at ground state have been studied by density functional theory with a local spin density approximation. We have found that the magnetic moments of Mn ions in the tetrahedron and those of Mn ions in the crown of the Mn12O12 molecule align antiferromagnetically. The average moment per Mn ion is about 3.07μB in the tetrahedron and 4.07μB in the crown. The total spin amounts to 20.0μB which is in agreement with recent experimental results. The significant difference of magnetic moments between Mn ions at two sites is attributed to the different exchange splitting of 3d orbitals. However, the charge difference between the two kinds of Mn ions is as small as 0.22 electrons. The charge density and the spin density exhibit strong directional dependence, which indicates the strong anisotropy in this molecule.

Crystalline and magnetic properties of MnAs under pressure

Lattice constants and magnetization in MnAs were measured under pressures up to 24 kbar at room temperature and 10 kbar at 80 K, respectively. Compresibilities in the MnP-type phase was obtained at pressures from 8 to 24 kbar. Magnetic moment of Mn ion was about 1.6 μ B under 8—10 kbar.

Antiparallel ordering of Mn and Nd magnetic moments in Nd 0.7Ba 0.3MnO 3

The crystal and magnetic structures of the giant magnetoresistive compound Nd 0.7Ba 0.3MnO 3 have been investigated by means of neutron powder diffraction. The nuclear structure remains orthorhombic within the temperature range 1.5–300 K. As expected from the higher size of Ba-ion radii, the buckling as well as the distortion of MnO 6 octahedra are less pronounced than in the parent compounds Nd 0.7A′ 0.3MnO 3 (A′ = Ca, Sr). At 1.5 K, we observe a ferromagnetic ordering of both Nd and Mn magnetic moments along the b-axis. However, Nd and Mn moments point in opposite directions. The saturated magnetic moment of Mn ions is 3.45 μ B, whereas the magnetic moment of Nd ions reaches 0.45 μ B at 1.5 K. The Curie temperatures are T C(Mn) = 142 K and T C(Nd) = 20 K.

A modulated magnetic structure in CaMn 7O 12

The magnetic structure of CaMn 7O 12 was investigated by neutron powder diffraction measurements in temperatures from 1.7 K to RT. We observed several magnetic reflections which appear around 86 K. Their 2θ positions shift considerably and get broader between 30 and 50 K, where an anomaly in magnetic susceptibility exists. These phenomena can be due to a modulated magnetic arrangement of the magnetic moments of Mn ions with a strongly temperature-dependent modulation period. An estimate of the value of the magnetic moments is given.

Magnetooptical Properties of GaAs:Mn

There are two basic issues which bring GaAs:Mn to be an interesting system. The first one is the problem of Mn dopant in III—V compounds, which has been studied for many years but the actual situation is not well understood yet [1-7]. The mostly accepted model assumes that the neutral Mn acceptor center is formed of Mn3+ core with tightly bound electron and a weakly bound hole (Mn 2+ + hole) [1] (the socalled magnetic acceptor complex (MAC)). This model explains the results of EPR experiments but fails to describe magnetization and susceptibility data [4]. On the other hand, randomly distributed, localized magnetic moments of Mn ions classify GaAs:Mn to the group of the socalled diluted magnetic Semiconduction (DMS) [7]. So far most of the research has been focused on II—VI DMS, whereas results for III—V compounds are very limited. In this communication we report the results of exchange-induced band splitting of bulk GaAs heavily doped with Mn. This study was done by means of the free exciton magnetospectroscopy. Reflectance and the degree of polarization of reflectance in Faraday configuration were measured at T = 2.0 K and magnetic field Β < 5 T for several crystals with different Mn concentration (below 0.1% mole). Additionally magnetization was measured at the same temperature and the field range using a SQUID magnetometer. The Ga1xMnxΑs crystals used in this work were grown by the Czochralski method. Single-phase crystals were obtained only for low Mn concentrations, x < 0.001. We selected three crystals with

Measurements of g-factor and exchange integral J in Hg 1−x Mn xTe by means of tunneling

In dynamic conductivity d I/d V vs. V of tunnel junctions HgMnTe/Al 2O 3/Pb the peaks at V = 0 in low magnetic fields and the dips in higher fields are observed. These zero bias anomalies (ZBA) are interpreted in terms of interaction between tunneling electrons and magnetic moments of Mn ions. From the dependence of ZBA on magnetic field the g-factor vs. H and the exchange integral J have been deduced.