NiP:Mn as a potential magnetic contacting material to Cd1−xMnxTe

Injection of spin-polarized current into spintronic devices is a challenge to the semiconductor physicists and technologists. II-VI compound semiconductors can act as the spin aligner on the top of GaAs light emitting diode. However, II-VI compound semiconductor like Cd_1−xMn_xTe is still suffering from contacting problem. Application of electroless deposited magnetic NiP:Mn contact would enhance efficient current injection into Cd_1−xMn_xTe than the standard gold contact. A technique for electroless deposition of NiP:Mn on Cd_1−xMn_xTe have been described here. The electronic and magnetic properties of the contact material NiP:Mn and the contact performance of NiP:Mn relative to evaporated gold have been evaluated. The contact fulfills the requirements of resistivity and ferromagnetism for application to Cd_1−xMn_xTe.     

Magnetic anisotropy of Tb1−xGdxMn6Sn6 compounds

Magnetization curves of Tb_1−xGd_xMn₆Sn₆ compounds (0?x?1) have been measured for aligned powder samples in the temperature range 4.2–300 K in pulsed magnetic fields up to 30 T. Temperature and concentration dependences of the magnetocrystalline anisotropy constants K₁ and K₂ and concentration dependence of the temperature of spontaneous spin-reorientation transition have been determined. Using these data, we estimated the contribution of the manganese and terbium atoms to the magnetic anisotropy of Tb_1−xGd_xMn₆Sn₆ and analyzed the origin of the appearance of field-induced first-order magnetic phase transition in these compounds.     

Magnetic field dependence of the energy levels in CdTe-Cd(Mn)Te double quantum well structures

We show that if the valence band offset between CdTe and Cd_1-xMn_xTe alloys is not too large, magneto-photoluminescence experiments performed on CdTe-Cd_1-xMn_xTe-Cd_1-yMn_yTe double quantum wells should yield direct informations on this offset: the structure changes from a type I configuration (where electron and hole are mostly localized within CdTe layer) prevailing at zero magnetic field to a type II configuration (electron in CdTe layer, hole in Cd_1-yMn_yTe layer) at large magnetic field.     

Thermoelectric power in ferromagnetic Pb0.16Sn0.72Mn0.12Te semiconductor

Thermoelectric power was studied in semimagnetic (diluted magnetic) Pb_1−x−ySn_yMn_xTe (x=0.12,y=0.72) semiconductor in the temperature range T=10–100 K covering both ferromagnetic and paramagnetic range of temperatures of this material. In addition to standard diffusion contribution to the thermoelectric power (α_D∝T), we found in PbSnMnTe an additional “magnetic” contribution (α_FM). Employing the effect of carrier-concentration-controlled ferromagnetism in PbSnMnTe, we demonstrate that the temperature dependence of α_FM(T) shows a clear maximum at the ferromagnetic Curie temperature. This experimental finding is discussed in terms of Kasuya model for the thermoelectric properties of diluted magnetic metallic systems with sd-exchange interaction.     

Room-temperature ferromagnetism in Sn1−xMnxO2 nanocrystalline thin films prepared by ultrasonic spray pyrolysis

Sn_1−xMn_xO₂ (x=0.01-0.05) thin films were synthesized on quartz substrate using an inexpensive ultrasonic spray pyrolysis technique. The influence of doping concentration and substrate temperature on structural and magnetic properties of Sn_1−xMn_xO₂ thin films was systematically investigated. X-ray diffraction (XRD) studies of these films reflect that the Mn³⁺ ions have substituted Sn⁴⁺ ions without changing the tetragonal rutile structure of pure SnO₂. A linear increase in c-axis lattice constant has been observed with corresponding increase in Mn concentration. No impurity phase was detected in XRD patterns even after doping 5 at% of Mn. A systematic change in magnetic behavior from ferromagnetic to paramagnetic was observed with increase in substrate temperature from 500 to 700 °C for Sn_1−xMn_xO₂ (x=0.01) films. Magnetic studies reveal room-temperature ferromagnetism (RTFM) with 3.61×10⁻⁴ emu saturation magnetization and 92 Oe coercivity in case of Sn_1−xMn_xO₂ (x=0.01) films deposited at 500 °C. However, paramagnetic behavior was observed for the films deposited at a higher substrate temperature of 700 °C. The presence of room-temperature ferromagnetism in these films was observed to have an intrinsic origin and could be obtained by controlling the substrate temperature and Mn doping concentration.     

Electrical and ferromagnetic properties of Tb-doped indium-tin oxide films fabricated by sol-gel method

The electrical and ferromagnetic properties of (In_0.9−xTb_xSn_0.1)₂O₃ and (In_0.99−yTb_0.01Sn_y)₂O₃ films fabricated by sol-gel method have been investigated. All the films show room temperature ferromagnetism. The magnetic moment per Tb ion of (In_0.9−xTb_xSn_0.1)₂O₃ films first increases and then decreases with the increasing Tb content. The variation of conductivity with Tb content is coincident with that of the magnetic moment. Furthermore, the conductivity and magnetic moment variations with Sn content y in (In_0.99−yTb_0.01Sn_y)₂O₃ films also have the similar trend. These results imply that the ferromagnetism may originate from the carrier-mediated mechanism.     

The large low-field magnetic entropy changes in Ni43Mn46Sn11−xSbx alloys

A series of Ni₄₃Mn₄₆Sn_11−xSb_x (x=0, 1, and 3) alloys were prepared by an arc melting method. The martensitic transition shifts to higher temperature with the increasing Sb content. The isothermal magnetization curves and Arrott plots around martensitic transition temperatures show a typical metamagnetic behavior. Under a low applied magnetic field of 10 kOe, large magnetic entropy changes around the martensitic transition temperature are 10.4, 8.9, and 7.3 J/kg K, for x=0, 1, and 3, respectively. The origin of the large magnetic entropy changes and potential application for Ni₄₃Mn₄₆Sn_11−xSb_x alloys as working substances in magnetic refrigeration are discussed.     

X-ray photoelectron study of Sn1−xMnxTe semimagnetic semiconductors

X-ray photoelectron (XPS) studies of core-levels in Sn_1−xMn_xTe (x < 0.1) semimagnetic semiconductors have been performed. The spectra were acquired under UHV conditions from the clean (as-cleaved or in-situ scraped) crystal surface. The single-phase NaCl structure of the alloys studied was verified by X-ray diffraction (XRD). The structure of Sn 3d and Te 3d core-levels in SnMnTe was found fully consistent with that of SnTe. Remarkable qualitative similarity of the Mn 2p spectrum of Sn_1−xMn_xTe (x = 0.09) with the case of zinc-blende MnTe [R.J. Iwanowski, M.H. Heinonen, E. Janik, Chem. Phys. Lett. 387 (2004) 110] has been shown: (1) the same binding energies (BEs) of the main contributions to the Mn 2p_3/2 line, related to Mn²⁺ state of the bulk MnTe bond; (2) occurrence of low BE component in the Mn 2p spectrum, indicative of clean-surface species containing reduced-valence Mn ions (i.e. Mn^q+, where 0 < q < 2); (3) strong satellites of the 2p_3/2 (Mn²⁺ related) parent lines. In SnMnTe, the highest intensity ratio of the satellite to main peak (ever reported for Mn 2p photoelectron spectrum) was revealed; this was interpreted in terms of the so-called charge-transfer model.     

Composition dependence of magnetic anisotropy and quadratic magnetooptical effect in epitaxial films of the Heusler alloy Co2MnGe

Magnetic anisotropy and magnetooptic Kerr effect for epitaxial films of Co_xMn_yGe_1−x−y grown on Ge (1 1 1) substrates have been studied systematically in the compositional vicinity of the Heusler alloy Co₂MnGe. A large quadratic magnetooptic Kerr effect has been observed within a narrow region of composition centered around the Co to Mn atomic ratio of 2. The effect has been used to probe and quantify the magnetic anisotropy of the system, which is shown to have a strong sixfold in-plane component accompanied by a weak uniaxial component at room temperature. These properties are shown to depend sensitively on atomic ratio between Co and Mn, indicating the presence of an intrinsic composition-driven phenomenon.     

Intracenter luminescence of Mn2+ in Cd1−x MnxTe and Cd1−x−y MnxMgyTe under intense optical pumping

A comparative analysis of the kinetic properties of intracenter 3d luminescence of Mn²⁺ ions in the dilute magnetic superconductors Cd_1?x Mn_xTe and Cd_1?x?y Mn_xMg_yTe is carried out. The influence of relative concentrations of the cation components on the position of the intracenter luminescence peak indicates that the introduction of magnesium enhances crystal field fluctuations. As a result, the processes facilitating nonlinear quenching of luminescence are suppressed. The kinetics of 3d-luminescence quenching in Cd_1?x Mn_xTe are accelerated considerably upon elevation of optical excitation level due to the evolution of cooperative processes in the system of excited manganese ions.     

First-principles study of electronic structure and magnetic properties of doped SnO2 (rutile) with single and double impurities

Using the augmented spherical wave method, the electronic structure and magnetic properties of the rutile SnO₂ doped with single and double impurities: Sn_1−xMn_xO₂, Sn_1−xW_xO₂, and Sn_1−2xMn_xW_xO₂ with x=0.0625, have been studied. The scalar-relativistic implementation with a generalized gradient approximation functional has been used for treating the effects of exchange and correlation. The ground state of Mn-, and W-doped SnO₂ systems have a total magnetic moments of 3 and 2 μ_B, respectively. The half-metallic nature appears in Sn_1−2xMn_xW_xO₂, which makes them suitable as spintronic systems with total magnetic moment of 5 μ_B. The advantages of doping SnO₂ with double impurities are investigated in this work. The total moment of the system, the local magnetic moments of the impurities, and their oxidation states are also discussed. Since there are two possible couplings between the impurities, we studied both configurations (ferromagnetic and antiferromagnetic) for double-impurities-doped SnO₂. Magnetic properties and interatomic exchange have been computed for various distances between Mn and W. The indirect exchange between double impurities has similarities with the Zener mechanism in transition metal oxides. Based on the interaction between localized moments, via hybridization between impurities orbitals with the host oxygen, a double exchange mechanism is proposed to explain the ferromagnetism of our system.     

Excitonic magnetic polaron dynamics of MBE grown CdTe/Cd1 − xMnxTe,Cd1 − xMnxTe/Cd1 − vMgyTe single quantum wells in magneti fields

Excitonic lifetimes in Cd_1 − xMn_Ue2Te, Cd_1 − xMg_xTe epilayers and CdTe/Cd_1 − xMn_xTe, Cd_1 − xMn_xTe/Cd_1 − vMg_yTe single quantum wells with different well widths and Mn, Mg compositions are investigated. The excitonic lifetimes are found to reduce drastically by applying external magnetic fields to samples with giant Zeeman splittings. The observed phenomenon is interpreted in terms of the PL decay time contribution from the long-life dark excitons which can convert to excitons for recombinations by a spin-flip process. We attribute the lifetime reduction to the depletion of dark excitons due to their crossing over the exciton energies for dipole allowed transitions in magnetic fields.     

The behavior of Shubinikov-de Haas oscillations in Hg1−x−yCdxMnyTe alloys

The transverse and longitudinal magnetoresistance are measured on a quaternary semimagnetic semiconductor, n-type Hg_1−x−yCd_xMn_yTe with 0.01 < x < 0.23 and y ≈ 0.14, at different temperatures. The peaks of the Landau-spin states are assigned using the selection rules already developed for HgCdTe. The Landau-spin states are modified by an exchange interaction between the Mn²⁺ ions localized spin and the band electrons, thus it becomes possible to compare directly the extent of the spin modification between the negative gap side and the open gap side of the new alloys.     

Ferromagnetic semiconductor Ge1−x−ySnxMnyTe with phase transformation of ferroelectric type

It is expected that joint existence of ferromagnetic properties and ferroelectric structural phase transition in diluted magnetic semiconductors IV-VI leads to new possibilities of these materials. Temperature of ferroelectric transition for such crystals can be tuned by the change of Sn/Ge ratio. Magnetic susceptibility, Hall effect, resistivity and thermoelectric power of Ge_1−x−ySn_xMn_yTe single crystals grown by Bridgeman method (x=0.083-0.115; y=0.025-0.124) were investigated within 4.2-300 K. An existence of FM ordering at T_C∼50 K probably due to indirect exchange interaction between Mn ions via degenerated hole gas was revealed. A divergence of magnetic moment temperature dependences at T?T_C in field-cooled and zero-field-cooled regimes is obliged to magnetic clusters which are responsible for superparamagnetism at T>T_C≈T_f (freezing temperature) and become ferromagnetic at T_C arranging spin glass state at T<T_f≈T_C. Phase transition of ferroelectric type at T≈46 K was revealed. Anomalous Hall effect which allows to determine magnetic moment was observed.     

Formation mechanism of ferromagnetism in Si1−xMnx diluted magnetic semiconductors

Si_1−xMn_x diluted magnetic semiconductor (DMS) bulks were formed by using an implantation and annealing method. Energy dispersive X-ray fluorescence, transmission electron microscopy (TEM), and double-crystal rocking X-ray diffraction (DCRXD) measurements showed that the grown materials were Si_1−xMn_x crystalline bulks. Hall effect measurements showed that annealed Si_1−xMn_x bulks were p-type semiconductors. The magnetization curve as a function of the magnetic field clearly showed that the ferromagnetism in the annealed Si_1−xMn_x bulks originated from the interaction between interstitial and substitutional Mn⁺ ions, which was confirmed by the DCRXD measurements. The magnetization curve as a function of the temperature showed that the ferromagnetic transition temperature was approximately 75 K. The present results can help to improve understanding of the formation mechanism of ferromagnetism in Si_1−xMn_x DMS bulks.     

A study of room-temperature ferromagnetism in transition metal and fluorine-doped spray-pyrolyzed SnO2 thin films

Room-temperature ferromagnetism has been observed in Co- or Mn-doped SnO₂ and Co- and F-co-doped SnO₂ thin films. A maximum magnetic moment of 0.80μ_B/Co ion has been observed for Sn_0.90Co_0.10O_1.925−δF_0.075 thin films, whereas in the case of Sn_1−xMn_xO_2−δ it was 0.18μ_B/Mn ion for x=0.10. The magnetization of both Sn_1−xCo_xO_2−δ and Sn_1−xCo_xO_2−y−δF_y thin films depends on the free carrier concentration. An anomalous Hall effect has been observed in the case of Co-doped SnO₂ films. However, the same was not observed in the case of Mn-doped SnO₂ thin films. Carrier-mediated interaction is convincingly proved to be the cause of ferromagnetism in the case of Co:SnO₂. It is, however, proposed that no carrier-mediated interaction exists in the case of Mn:SnO₂. Present studies indicate that dopants and hence electronic cloud-lattice interaction plays an important role in inducing ferromagnetism.     

Microstructure characterization and magnetic behavior of NiAlxFe2−xO4 and Ni1−yMnyAl0.2Fe1.8O4 ferrites

NiAl_xFe_2−xO₄ and Ni_1−yMn_yAl_0.2Fe_1.8O₄ ferrites were prepared by the conventional ceramic method and were characterized by X-ray diffraction, scanning electron microscopy, and magnetic measurements. The single spinel phase was confirmed for all prepared samples. A proper explanation of data is possible if the Al³⁺ ions are assumed to replace Fe³⁺ ions in the A and B sites simultaneously for NiAl_xFe_2−xO₄ ferrites, and if the Mn²⁺ ions are assumed to replace Ni²⁺ ions in the B sites for Ni_1−yMn_yAl_0.2Fe_1.8O₄ ferrites. Microstructural factors play an important role in the magnetic behavior of Ni_1−yMn_yAl_0.2Fe_1.8O₄ ferrites with large Mn²⁺ content.     

Magnetic field effect on transitions between direct and indirect excitons in diluted magnetic semiconductor double quantum wells

Transitions between direct and indirect excitons with change of magnetic field in double quantum well heterostructure Cd_1−xMg_xTe/Cd_1−yMg_yTe/Cd_1−xMg_xTe/Cd_1−zMn_zTe/Cd_1−xMg_xTe in external magnetic field are studied. The structure contains diluted magnetic semiconductor (Cd,Mn)Te layer that forms magnetic quantum well with the depth depending on the magnetic field intensity. Above some magnetic field the indirect exciton becomes the lowest excited state of the system. The indirect exciton lifetime exceeds by several orders of magnitude of the direct exciton one. The range of quantum well widths for which the indirect exciton is the exciton lowest state was estimated for the proposed system.     

Magnetic properties of the Ce2Fe17−xMnx helical magnets up to high magnetic fields

Magnetic properties of the Ce₂Fe_17−xMn_x, x=0–2, alloys in magnetic fields up to 40 T are reported. The compounds with x=0.5–1 are helical antiferromagnets and those with 1<x?2 are helical ferromagnets or helical antiferromagnets at low and high T, respectively. Mn ions in the system carry average magnetic moment of 3.0±0.2 μ_B that couple antiparallelly to the Fe moments. Easy-plane magnetic anisotropy in the Ce₂Fe_17−xMn_x compounds weakens upon substitution of Mn for Fe. The absolute value of the first anisotropy constant in the Ce₂Fe_17−xMn_x helical ferromagnets decreases slower with increasing temperature than that calculated from the third power of the spontaneous magnetization. Noticeable magnetic hysteresis in the Ce₂Fe_17−xMn_x, x=0.5–2, helical magnets over the whole range of magnetic fields reflects mainly irreversible deformation of the helical magnetic structure during the magnetization of the compounds. A contribution from short-range order (SRO) magnetic clusters to the magnetic hysteresis of the helical magnets has been also estimated.