Magnetic resonance in Ge0.99Mn0.01 nanowires

The contributions of several different subsystems to the magnetic properties of Ge_0.99Mn_0.01 nanowires are distinguished. The ferromagnetic resonance spectrum is found to have four components, two of which have the same temperature dependence and a Lorentzian shape. Presumably, these components correspond to the excitation of spin waves in the Mn³⁺ ion subsystem under the simultaneous influence of exchange and dipole-dipole interactions. There is also another Lorentzian-shaped component corresponding to resonance in the subsystem of localized Mn²⁺ centers. The fourth spectrum component has an asymmetric Dyson shape and is related to the resonance of mobile paramagnetic centers. A correlation is found between the temperature dependences of the spectral parameters of the magnetic resonances of the localized centers (Mn³⁺ and Mn²⁺ ions) and the charge carrier subsystem. This correlation indicates that the ferromagnetic exchange between the localized centers is due to carrier spin transport.     

Magnetic,electrical transport and electron spin resonance studies of Fe-doped manganite LaMn0.7Fe0.3O3+δ

We have investigated the magnetic, electrical transport and electron spin resonance (ESR) properties of polycrystalline Fe-doped manganite LaMn_0.7Fe_0.3O_3+δ prepared by sol–gel method. A typical cluster-glass feature is presented by DC magnetization and AC susceptibility measurements and a sharp but shallow memory effect was observed. Symmetrical Lorentzian lines of the Mn/Fe spectra were detected above 120 K, where the sample is a paramagnetic (PM) insulator. When the temperature decreases from 120 K, magnetic clusters contributed from ferromagnetic (FM) interaction between Mn³⁺ and Mn³⁺/Fe³⁺ ions develop and coexist with PM phase. At lower temperature, these FM clusters compete with antiferromagnetic (AFM) ones between Fe³⁺ ions, which are associated with a distinct field-cooled (FC) effect in characteristic of cluster-glass state.     

Origin of the electron spin resonance signal in the manganites: from polarons to phase separation

In the manganites L_1?xM_xMnO₃ (L = La, Nd, Pr, …; M = Sr, Ba, Ca, …), the doping concentration introduces a mixed valence (Mn³⁺, Mn⁴⁺) which governs the magnetic and electric properties of the compound. Mn³⁺ (S = 2) is scarcely observed in electron spin resonance (ESR). In contrast, Mn⁴⁺ (S = 3/2), is a good ESR probe. However, X-band measurements show an enhanced Mn⁴⁺ susceptibility, which is the signature of some kind of coupling of the Mn⁴⁺ ions with the Mn³⁺ ions, but its exact nature is still controversial. We present multifrequency ESR experiments (9–385 GHz) obtained on different systems (La_1?δMnO₃, La_1?xMnO₃, La_1?xCa_xMnO₃, and Nd_1?xCa_xMnO₃) in the low-concentration range (0 <x< 0.33). In the paramagnetic regime, the Mn³⁺ spectrum cannot be observed because of fast relaxation. The signal arises from polarons, whose size, temperature and magnetic field dependences vary with M andx. The single line observed in the metallic compound evolves towards a double-peak structure visible at high frequency in La_0.97MnO₃. Its evolution with temperature below the magnetic transition reveals the presence of manganese ions in a different magnetic environment, i.e., phase separation. The magnetic order of the separated phase is not ferromagnetic. It is a more complex order, which depends substantially on the nature of the cation M.     

Atomic 6p-Tl0 centers in ferroelectric Rb2ZnCl4 crystals

Abstract

Several Tl⁰ (6s²6p ¹)-type paramagnetic centers, produced by low temperature X-ray irradiation, were observed and studied by electron spin resonance (ESR) in the orthorhombic ferroelectric phase of thallium doped Rb₂ZnCl₄ crystals. The centers were formed by electron trapping at Tl⁺ ions localized substitutionally at Rb⁺ sites. The number and properties of the observed centers account for the tripling of the unit cell in the ferroelectric phase.     

Exchange interaction of S state ions with charge carriers in SnTe

ESR investigations of Mn, Eu and Gd in highly degenerate SnTe - a p-type semiconductor with metallic behaviour - prove the existence of an exchange interaction between localized magnetic moments and charge carriers. The ratio of the exchange parameters J_Mn and J_Eu between charge carriers and Mn or Eu ions, respectively, amounts to |J_Mn/J_Eu| = 8 ± 1.5. The consequence this result has on long range spin-spin interaction via charge carriers as well as on hyperfine interaction is discussed.     

The transition from dynamics to statics in the electron-spin-resonance spectra of impurity Mn2+ ions in strontium titanate

The electron-spin-resonance (ESR) spectra of SrTiO₃:Mn single crystals have been investigated. Results unambiguously indicate that the impurity center formed by an Mn²⁺ ion has a dynamic nature. In the high temperature range (T > 100 K), ESR spectra of Mn²⁺ ions reveal cubic symmetry; the spectrum is found to broaden significantly with a decrease in temperature. Upon cooling to T < 10 K, low-symmetry centers of Mn²⁺ ions with a strong orientational dependence emerge in the spectra. Temperature evolution of the ESR spectrum can be described within the model of a dynamic off-center Mn²⁺ ion substituting for the Sr²⁺ ion, with a transition to the static regime at low temperatures with an average localization energy of ～2.4 ± 0.4 meV for Mn²⁺ centers due to random deformations.     

A Low Temperature (10 K) High-Frequency (208 GHz) EPR Study of the Non-Kramers Ion Mn3+ in a MnMo6Se8 Single Crystal

A high-frequency (208 GHz) electron paramagnetic resonance (EPR) study on Mn³⁺ (3d⁴, S = 2) ions embedded in a MnMo₆Se₈ single crystal has been performed at 10 K. The experimental spectra reveal the presence of only one set of EPR lines from Mn³⁺ ions, whose magnetic axes are oriented along the crystal axes. The spin-Hamiltonian parameters are evaluated by the method of least-squares, fitting all the observed line positions simultaneously, for the three orthogonal orientations of the external magnetic field. The symmetry of the spin Hamiltonian at the site of the Mn³⁺ ions has been deduced from the EPR spectra.     

Observation of helicon-excited electron paramagnetic resonance in a high-mobility semiconductor

Helicon waves can be exploited in EPR studies of localized magnetic moments in high-conductivity semiconductors when the free carriers have small effective mass and high mobility. In an electron plasma helicons have precisely the polarization required to elicit EPR, and the plasma background actually enhances the resonance intensity. Microwave transmission experiments on Hg_1-xMn_xTe, a narrow-gap semiconductor with localized Mn⁺⁺ magnetic moments, are described to illustrate this effect.     

Temperature dependence of phase separation and magnetic anisotropy by electron spin resonance in Pr<Subscript>0.6</Subscript> Ca<Subscript>0.4</Subscript> Mn<Subscript>0.9</Subscript> Ru<Subscript>0.1</Subscript>O<Subscript>3</Subscript>

Electron spin resonance (ESR) measurements have been performed on polycrystalline samples of Pr_0.6Ca_0.4Mn_1-xRu_xO₃ (x = 0, 0.1). The substitution of Ru in the Mn-site strengthens ferromagnetic interactions due to the double exchange between the Mn³⁺ and Mn⁴⁺ species and super-exchange between the Ru⁵⁺ and Mn³⁺ species. The temperature dependence of the ESR spectra indicates development of magnetic phase separation in Pr_0.6Ca_0.4Mn_0.9Ru_0.1O₃ in contrast with the un-doped sample.     

Submillimeter electron-nuclear excitation spectra in CsCdBr3:Ln3+ (Ln=Tm, Ho) crystals

The ESR spectra of single and pair impurity centers of thulium and holmium ions in CsCdBr₃:Tm³⁺ and CsCdBr₃:Ho³⁺ crystals are measured in the frequency range 160-400 GHz. Analysis of the characteristic features of the hyperfine structure of the ESR lines and analysis of the variations in the spectra as a function of the temperature and external magnetic field shows that the Ln³⁺ ions substitute for Cd²⁺ ions and predominantly form symmetric pair centers of the type Ln³⁺-(vacancy at a neighboring Cd²⁺ site)-Ln³⁺. The ESR spectra of CsCdBr₃: Ln³⁺ crystals are used to make a positive identification of the optical spectra of selective laser excitation. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 7, 535–540 (10 April 1997)     

ESR experiments with egg shells of chickens

The electron spin resonance spectra fromGallus domesticus egg shells exhibit a strong free radical singlet, a spectrum due to Mn²⁺ ions in a calcite site, a low field line line atg≈30/7 due to Mn²⁺ in a rhombic site, and spectral lines arising from Fe³⁺ ions. Details of the ESR spectral lines did not correlate with fertile, non-fertile or color type egg-shell characteristics.     

Theoretical studies of absorption spectra and microstructure of Ni2+ at the octahedral site of the NiFe2O4 nanoparticle

The optical absorption spectra, microstructure and electronic spin resonance parameters (electronic spin resonance (ESR) g factor) for Ni²⁺ ions at octahedral centers of nickel ferrite nanoparticles are calculated from the two-spin–orbit-parameter model. The effect of spin–orbital coupling of the central metal 3d⁸ ions and ligand oxygen ions has been taken into account in the full energy matrix and ESR g formula. The calculated results are in good agreement with the observed values. In addition, the microstructures of Ni²⁺ ions at octahedral centers in NiFe₂O₄ are reasonably determined from the calculations.     

Oxygen vacancy and dopant concentration dependent magnetic properties of Mn doped TiO2 nanoparticle

Mn doped TiO₂ nanoparticles are synthesized by sol–gel method. Incorporation of Mn shifts the diffraction peak of TiO₂ to lower angle. The position and width of the Raman peak and photoluminescence intensity of the doped nanoparticles varies with oxygen vacancy and Mn doping level. The electron spin resonance spectra of the Mn doped TiO₂ show peaks at g = 1.99 and 4.39, characteristic of Mn²⁺ state. Reduction in the emission intensity, on Mn doping, is owing to the increase of nonradiative oxygen vacancy centers. Mn doped TiO₂, with 2% Mn, shows ferromagnetic ordering at low applied field. Paramagnetic contribution increases as Mn loading increases to 4% and 6%. Temperature dependent magnetic measurement shows a small kink in the ZFC curve at about 40 K, characteristic of Mn₃O₄. The ferromagnetic ordering is possibly due to the interaction of the neighboring Mn²⁺ ions via oxygen vacancy (F⁺ center). Increase in Mn concentration increases the fraction of Mn₃O₄ phase and thereby increases the paramagnetic ordering.     

EPR/FMR Investigation of Mn-Doped SiCN Ceramics

SiCN magnetic ceramics doped with Mn²⁺ ions were synthesized at the pyrolysis temperature of 1,100° C, using CERASET™ as liquid polymer precursor and polymer manganese(II) acetylacetonate as dopant, and investigated by electron paramagnetic resonance (EPR)/ferromagnetic resonance (FMR) technique. The predominant source of ferromagnetism in SiCN samples doped with Mn ions, as synthesized here, is the ensemble of ferromagnetic nanoparticles of Mn₅Si₃C _x incorporated into the amorphous SiC/Mn structure. The fluctuation of magnetization due to ferromagnetic Mn₅Si₃C_x particles significantly broadens the EPR lines at the phase-transition temperature (363 K). This is the first fabrication of a SiCN/Mn ceramic, which exhibits room-temperature ferromagnetism.     

Study of ESR spectra of Ce<Superscript>3+</Superscript> ions in polycrystalline Sr<Subscript>2</Subscript>B<Subscript>5</Subscript>O<Subscript>9</Subscript>Br

ESR spectra of Ce³⁺ ions in polycrystalline Sr₂B₅O₉Br were studied, and the two crystallographic positions of the Ce³⁺ ion in this compound were identified on the basis of the data obtained. The ESR spectrum of Ce³⁺ ions with local charge compensation contains a broad line indicating the existence of several types of charge compensation. ESR spectra of Ce³⁺ ions in samples activated additionally by K⁺ ions are similar to those of the regular Ce³⁺ centers, which indicates that the effect of the univalent cation on Ce³⁺ is negligible.     

Spin-wave resonance in Ge<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> films exhibiting percolation ferromagnetism

Magnetic properties of Ge_{1 ? x} Mn _x (x = 0.02, 0.04, 0.08) thin films obtained by ion-implanting Mn⁺ ions into single-crystal Ge plates are investigated. The contributions of the subsystem of dispersed Mn²⁺ ions, Ge³Mn⁵ ferromagnetic clusters, and Mn-enriched ferromagnetic domains of Ge to the magnetic moment of Ge_{1 ? x} Mn _x films are distinguished. In the subsystem of dispersed Mn²⁺ ions in Ge_{1 ? x} Mn _x films at temperatures below 10 K, a spin-wave resonance is observed in the magnetically ordered state due to percolation ferromagnetism. It is established that, in the films with percolation ferromagnetism, the exchange integrals determined from static measurements correspond to those determined by dynamic measurements.     

Low-Temperature Phase Transition Detected by ESR in ����-(BEDT-TTF)2IBr2 Single Crystals

Hysteresis of the electron spin resonance (ESR) spectra of localized charge carriers has been observed in ????-(BEDT-TTF)₂IBr₂ single crystals in the temperature range of 15?C30?K. The first-order phase transition has been detected by ESR components. Two lines observed in the ESR spectrum correspond to low-temperature and high-temperature phases.     

Photocontrolled magnetic resonance plasticity of γ-irradiated KCl:Fe crystals

A photocontrolled resonance decrease in microhardness, which is due to the application of mutually perpendicular static and microwave fields, in γ-irradiated KCl:Fe crystals has been revealed. It has been found that the magnetic plasticity of unirradiated γ-KCl:Fe crystals is due to the resonance effect of magnetic fields on two types of impurity centers: first, centers containing Fe²⁺-ν _c ion-vacancy pairs and, second, centers containing Fe⁺ ions. The illumination of γ-KCl:Fe crystals with F-light (with a wavelength of λ = 500–600 nm) is accompanied by rearrangement of the spectrum of electron paramagnetic resonance detected by a change in microhardness. The effect of F-light on the spectrum of magnetic resonance plasticity is manifested as the suppression of the spectra of Fe²⁺-ν _c ions with effective g-factors of 7.0 and 3.5 due to their recombination with F-electrons and reconstruction to Fe⁺ centers with g-factors of 2.2 and 4.1.     

Structural and Mössbauer studies of nanocrystalline Mn<Superscript>4+</Superscript>-doped Li<Subscript>0.5</Subscript>Fe<Subscript>2.5</Subscript>O<Subscript>4</Subscript> particles prepared by mechanical milling

The structure and magnetic properties of spinel-related Mn⁴⁺-doped Li_0.5Fe_2.5O₄ nanocrystalline particles of the composition Li_0.5Fe_2.25Mn_0.1875O₄, prepared by milling a pristine sample for different times, were investigated. The average crystallite and particle size, respectively, decreased form ～40 nm to ～10 nm and ～2.5 μm to ～10 nm with increasing milling time from 0 h to 70 h. Rietveld refinement of the XRD data of the non-milled sample show the Mn⁴⁺ dopant ions to substitute for Fe³⁺ at the octahedral B-sites of the spinel-related structure. The Mössbauer spectra of the milled ferrites indicate that more particles turn superparamagnetic with increasing milling time. The Mössbauer data collected at 78 K suggest that while in the non-milled sample the Mn⁴⁺ ions substitute for Fe³⁺ at the octahedral B-sites, this is reversed as milling proceeds with doped Mn⁴⁺ ions, balancing Fe³⁺ vacancies and possibly Li⁺ ions progressively migrate to the tetrahedral A-sites. This is supported by the slight increase observed in the magnetization of the milled samples relative to that of the non-milled one. The magnetic data suggest that in addition to the increasing superparamagentic component of the milled particles, thermal spin reversal and/or spin canting effects are possible at the surface layers of the nanoparticles.     

EPR investigation of the accumulation of F+ centers in irradiated MgO:Mn crystals

According to electron paramagnetic resonance spectra of MgO:Mn crystals irradiated in a reactor, the dependences of the concentration of F⁺ centers on the irradiation dose and on the content of impurities have been obtained. The strong influence of paramagnetic Mn²⁺ ions on the efficiency of the accumulation of F⁺ centers is determined.