X-Band ESR and51V NMR study of the Haldane system PbNi2−xMgxV2O8

The temperature and angular dependence of the X-band electron spin resonance (ESR) and⁵¹V nuclear magnetic resonance (NMR) spectra have been measured in a recently discovered Haldenegap system, PbNi_2-xMg_xV₂O₈ (0≤x≤0.24). The angular dependence of the ESR signal suggests that both the spin diffusion as well as the magnetic anisotropy determine the electronic spin correlation functions. However, in doped samples the magnetic anisotropy increasingly dominates the spin dynamics on cooling. The huge broadening of the⁵¹V NMR spectra in doped samples at low temperatures provides evidence for localized magnetic moments in the vicinity of the Mg impurities. Locally distorted structure around each Mg impurity may slightly modify the magnetic interactions and be potentially responsible for the antiferromagnetic ordering (belowT _N≈ 3.5K) in doped compositions.     

The ground-state magnetic moments of odd-mass Hf isotopes

In this paper the Quasiparticle-Phonon Nuclear Model (QPNM), based on QRPA (Quasiparticle Random Phase Approximation) phonons, has been utilized to investigate spin polarization effects on the groundstate magnetic properties such as intrinsic magnetic moment (g _K ) and effective spin gyromagnetic factor (g _s ^eff. ) of odd-mass deformed ^165–179Hf isotopes with K > 1/2. Investigations of the spin polarization effects of the even core on the magnetic moments show that the spin gyromagnetic factors (g _s ) of the nucleons in the nucleus differ noticeably from the corresponding values for free nucleons and that the spin-spin interactions play an important role in the re-normalization of g _s factors of the odd-mass ^165–179Hf isotopes. In addition, some theoretical predictions are presented for the magnetic moments of ¹⁶⁵Hf, ¹⁶⁷Hf, and ¹⁶⁹Hf, whose ground state magnetic moments haven’t been experimentally determined yet.     

Dielectric and proton relaxation from ammonium ion motion in alum

Dielectric losses and proton spin lattice relaxation T₁ and T_1? give identical correlation times in NH₄Al(SO₄)₂ · 12H₂O from 75 to 200 K. This is explained as hopping of NH⁺₄ between two positions with different orientations and electric dipole moments.     

Measurement of the electric quadrupole moments of 26–29Na

The nuclear electric quadrupole moments of the isotopes ²⁶Na, ²⁷Na, ²⁸Na and ²⁹Na were measured by -NMR spectroscopy in single crystals of LiNbO₃ and NaNO₃. High degrees of nuclear polarization were produced by optical pumping of the sodium atoms in a fast beam with a collinear laser beam. The polarized nuclei were implanted into the crystals and NMR signals were observed in the -decay asymmetries. Preparatory measurements also yielded improved values for the magnetic moments of ^27-31Na and confirmed the spin I=3/2 for ³¹Na. The results are discussed in comparison with large-basis shell model calculations. Received: 1 February 2000 / Accepted: 3 April 2000     

Local magnetization of Co andMn impurities in the reentrant spin glass Au0.82Fe0.18

The low-temperature nuclear orientation technique has been used to study the magnetic behaviour of⁶⁰Co and⁵⁴Mn impurity atoms in the reentrant spin glass Au_0.82Fe_0.18. The results obtained for⁶⁰Co indicate that Co moments follow the distribution of Fe directions. In contrast, Mn moments show a spread directional distribution. These results are the consequence of the different character of Mn-Fe andFe-Fe interactions at short distances.     

Evidence of reduction in spin disorder by Ho3+ doping in La0.7Ca0.3MnO

We have shown in a recent study that substitution of Ho³⁺ ions (4f¹⁰; magnetic momen _μB) in La_0.7Ca_0.3MnO₃ causes significant reduction in electrical resistivity compared with Y³⁺ (4d⁰; non-magnetic) ion substitution. This reduction in resistivity was attributed to the reduced spin disorder scattering in La_0.7Ca_0.3MnO₃ samples containing magnetic Ho³⁺. We have estimated the Mn-spin canting angles in Ho³⁺ - and Y³⁺-doped La_0.7Ca_0.3MnO₃ compounds from the resistivity data using the magnetic localization model. We find that the canting angles of the Mn spins in the Ho³⁺ doped compounds are smaller than those obtained for the Y³⁺-doped compounds for all compositions and at all applied magnetic fields, showing clearly a reduction in the spin disorder in the former. The difference between the T _C values for Ho³⁺ - and Y³⁺-doped compounds for all compositions may be attributed to the presence of an internal field due to Ho³⁺ doping. This internal field may be responsible for the decrease in spin disorder in the Ho³⁺-doped compounds. The increase in the canting angles with increase in Ho³⁺ and Y³⁺ content could be attributed to the decrease in the strength of the ferromagnetic exchange interactions. A strong ferromagnetic coupling (as discussed recently by the present authors and co-workers) of Ho³⁺ moments with the Mn moments is responsible for the observed behaviour.     

Enhanced superhyperfine interaction on Ru3+ in Tm3Al5O12 and on Ru3+ and Yb3+ in Tm3Ga5O12

Measurements of the enhanced superhyperfine interaction linking the electron spin of an impurity EPR ion and the nuclear moments of Van Vleck host lattice ions are reported for Ru³⁺ in Tm₃Al₅O₁₂ and for Ru³⁺ and Yb³⁺ in Tm₃Ga₅O₁₂. The Ru³⁺ results appear to be the first reported where this interaction is large enough to give rise to a well resolved superhyperfine structure. For Yb³⁺ the observed temperature dependent line narrowing evidences the role of Tm spin fluctuations.     

Application of M?ssbauer spectroscopy in magnetism

An overview is provided on our recent work that applies ⁵⁷Fe M?ssbauer spectroscopy to specific problems in nanomagnetism. ⁵⁷Fe conversion electron M?ssbauer spectroscopy (CEMS) in conjunction with the ⁵⁷Fe probe layer technique as well as ⁵⁷Fe nuclear resonant scattering (NRS) were employed for the study of various nanoscale layered systems: (i) metastable fct-Fe; a strongly enhanced hyperfine magnetic field B_hf of ～39?T at 25?K was observed in ultrahigh vacuum (UHV) on uncoated three-monolayers thick epitaxial face-centered tetragonal (fct) ⁵⁷Fe(110) ultrathin films grown by molecular-beam epitaxy (MBE) on vicinal Pd(110) substrates; this indicates the presence of enhanced Fe local moments, μ_Fe, as predicted theoretically; (ii) Fe spin structure; by applying magnetic fields, the Fe spin structure during magnetization reversal in layered (Sm–Co)/Fe exchange spring magnets and in exchange-biased Fe/MnF₂ bilayers was proven to be non-collinear and depth-dependent; (iii) ferromagnet/semiconductor interfaces for electrical spin injection; CEMS was used as a diagnostic tool for the investigation of magnetism at the buried interface of Fe electrical contacts on the clean surface of GaAs(001) and GaAs(001)-based spin light-emitting diodes (spin LED) with in-plane or out-of-plane Fe spin orientation; the measured rather large average hyperfine field of ～27?T at 295?K and the distribution of hyperfine magnetic fields, P(B_hf), provide evidence for the absence of magnetically “dead” layers and the existence of relatively large Fe moments (μ_Fe ～ 1.8?μ_B) at the ferromagnet/semiconductor interface. - Finally, a short outlook is given for potential applications of M?ssbauer spectroscopy on topical subjects of nanomagnetism/spintronics.     

Boundary effects in finite Heisenberg antiferromagneticS = 1 chains:89Y NMR in Y2BaNi1−xMgxO5

By means of⁸⁹Y nuclear magnetic resonance (NMR) spectra direct evidence of staggered magnetization induced by a uniform field has been obtained in the Heisenberg antiferromagneticS = 1 chain Y₂BaNi_1?xMg_xO₅. A correspondence between the resonance lines and the lattice positions is established, providing an image of the alternating magnetic moments that develop around the Mg impurities at the chain boundaries. The amplitude of these moments is found to decrease exponentially from the edges, with a characteristic decay distance equal to the magnetic correlation length numerically evaluated for an infinite chain. While the magnetization pertaining to ions far from the boundaries behaves as in typical gapped systems, the edge spins exhibit anS = 1/2 Curie-like deviation. These results promote the NMR approach to access the spin-spin correlation function in antiferro-magnetic quantum spin systems at finite temperatures.     

First-principles investigation of the electronic structure and magnetism of Heusler alloys CoMnSb and Co2MnSb

The spin-polarized electronic band structures, density of states (DOS), and magnetic properties of Co-Mn-based Heusler alloys CoMnSb and Co₂MnSb have been studied by first-principles method. The calculations were performed by using the full-potential linearized augmented plane wave (FP-LAPW) within the spin-polarized density functional theory and generalized gradient approximation (GGA). Calculated electronic band structures and the density of states are discussed in terms of the contribution of Co 3d⁷4s², Mn 3d⁵4s², and Sb 5s²5p³ partial density of states and the spin magnetic moments were also calculated. The results reveal that both CoMnSb and Co₂MnSb have stable ferromagnetic ground state. They are ideal half-metallic (HM) ferromagnet at their equilibrium lattice constants. The calculated total spin magnetic moments are 3μ_B for CoMnSb and 6μ_B for Co₂MnSb per unit cell, which agree with the Slater-Pauling rule quite well.     

Critical nuclear relaxation in cobalt metal

Nuclear magnetic resonance of cobalt metal was investigated in the paramagnetic and ferromagnetic states and in the critical region below T_c. The Knight shift and spin lattice relaxation times were measured in the paramagnetic phase in the solid and liquid states from 1578 K to 1825 K. The resonant frequency, spin-lattice and spin-spin relaxation times were measured in the ferromagnetic phase from room temperature to 1385 K. The main part of (T₁T)^-1 results from fluctuating orbital moments in both phases except near T_c where this process forms the background for critical spin relaxation. The critical exponents for T^-1₁ and for the magnetization in the ferromagnetic state were found to be n' = 0.96 ± 0.07 and β = 0.308 ± 0.012, respectively.     

First-principles research on influence of C dopants on magnetic and electric properties of rocksalt MgS

<正>The 2×2×1 rocksalt C-doped MgS supercells are optimized and their magnetic and electric properties,including the half-metallicity,the conductivity and the supercell magnetic moments,are calculated or analysed by the first-principles researches based on the density functional theory.Results show that the concentration of C-dopants may cause important influence on the magnetic and the electric properties of rocksalt MgS.C dopants are inclined to have a scattering distribution.MgC_(0.0625)S_(0.9375),~aMgC_(0.1250)S_(0.8750) and MgC_(0.1875)S_(0.8125) have evident half-metallicity. They have wide spin energy gaps,thus high Curie temperature possibly.Their supercell magnetic moments are near to integral numbers 2.0,4.0 and 6.0μB.The main reason for spin polarization and half-metallicity of C-doped MgS is that there are sp hybridized orbitals in ligand compound ML_6 caused by covalent interaction between C-ions and Mg-ions.     

Li NMR in lithium borate glasses

In anticipation of using fluctuations in the nuclear dipolar and quadrupolar interaction as a probe of lithium ion motion in lithium borate glasses, the static values of these interactions were measured using a variety of echo techniques. The static quadrupolar echo spectrum of ⁷Li and a calculation of the dipolar interaction in crystalline Li₂B₄O₇ (same chemical composition as the glass under study) were used to estimate the strength of the two interactions. These indicate that the dipolar and quadrupolar interactions for ⁶Li will be of similar size and the dipolar interaction will be dominated by the unlike spin interaction between the ⁶Li and the ¹⁰B, ¹¹B spins. An appropriate theoretical model is proposed and explicit expressions for the echo amplitude are calculated in terms of the dipolar and quadrupolar second moments. This single spin model takes into account the quadrupolar interaction but treats the dipolar interaction as an effective magnetic field. Experimental results are presented which show the essential validity of the model and measurements lead to reasonable values for the dipolar and quadrupolar second moments. The relative merits of the various echo techniques are discussed.     

6Li NMR in lithium borate glasses

In anticipation of using fluctuations in the nuclear dipolar and quadrupolar interaction as a probe of lithium ion motion in lithium borate glasses, the static values of these interactions were measured using a variety of echo techniques. The static quadrupolar echo spectrum of ⁷Li and a calculation of the dipolar interaction in crystalline Li₂B₄O₇ (same chemical composition as the glass under study) were used to estimate the strength of the two interactions. These indicate that the dipolar and quadrupolar interactions for ⁶Li will be of similar size and the dipolar interaction will be dominated by the unlike spin interaction between the ⁶Li and the ¹⁰B, ¹¹B spins. An appropriate theoretical model is proposed and explicit expressions for the echo amplitude are calculated in terms of the dipolar and quadrupolar second moments. This single spin model takes into account the quadrupolar interaction but treats the dipolar interaction as an effective magnetic field. Experimental results are presented which show the essential validity of the model and measurements lead to reasonable values for the dipolar and quadrupolar second moments. The relative merits of the various echo techniques are discussed.     

Transferred hyperfine field in the pseudo-binary compound Y(Fe,Mn)2

The NMR of⁸⁹Y in Y(Fe_1−xMn_x)₂ has been observed. Two kinds of Mn moments were estimated by analyzing the⁸⁹Y hyperfine field: (1) the low spin state with about 0.6 μ_B in antiparallel to Fe moment and (2) the high spin state with about 2.8 μ_B in parallel to Fe moment. The magnetizations estimated from NMR results are in good agreement with those of magnetization measurements.     

Temperature dependence of the intrinsic Faraday rotation of ErFeO3

The Faraday rotation of ErFeO₃ as a function of temperature was measured from ambient down to the spin reorientation region (90 to 100°K) at a wavelength of 6070 Å. The intrinsic Faraday rotation increases gradually with decreasing temperature and then drops rapidly to zero in the spin reorientation region. It is concluded that the contribution of the polarized Er³⁺ magnetic moments to the measured rotation is negligible and that the Faraday effect is due almost entirely to the magnetic moments of the Fe³⁺ ions.     

Proton spin relaxation of butenes and butane in CaNaA zeolites

Using nmr pulse techniques the temperature dependence of proton spin relaxation times T₁ and T₂ of n-butene and butane molecules adsorbed on CaNaA zeolites with different content of Ca⁺⁺ ions has been investigated. The observed diminution of correlation times with rising degree of Ca⁺⁺ exchange can only be explained if translational motions, i.e. jumps between the supercages, dominate the proton spin relaxation of the adsorbates. Peculiarities in the microdynamical behaviour of the various n-butenes are in accordance with the model of electrostatic interactions between molecular dipole moments and electric fields in A zeolites as proposed by Tempère and Imelik in order to explain the stereoselectivity of the isomerization of n-butenes in A zeolites. Applying Torrey's well-known theory of nmr relaxation as dominated by translational jumps with arbitrary lengths, the mean time between two subsequent jumps has been estimated. In combination with measurements of self-diffusion coefficients by Kärger and Renner, these values lead to mean jump lengths which are reasonable compared with the distance of two neighbouring large zeolitic cavities. In order to interpret the methyl reorientation which dominates the longitudinal proton spin relaxation of the adsorbed hydrocarbons at lower temperatures, a model for calculating the intermolecular contribution to the relaxation rate has been discussed.     

Electronic states and spectroscopic properties of MgH in absence and presence of spin–orbit coupling − a configuration interaction study

Electronic spectrum of astrophysically important molecule magnesium hydride (MgH) has been studied using configuration interaction methodology excluding and including spin–orbit coupling. Potential energy curves of several spin-independent (Λ?S) electronic states have been constructed and spectroscopic constants of low-lying bound Λ?S states within 8.2 eV of term energy are reported in the first stage of calculations. The X²Σ⁺ is identified as the ground state in the Λ?S level. In the subsequent stage, the spin–orbit interaction has been incorporated and its effects on the potential energy curves and spectroscopic features of different electronic states of the species have been investigated. The X²Σ⁺_1/2 is identified as the spin–orbit (Ω) ground state of the species. Transition moments of several dipole-allowed transitions are computed in both the stages and radiative lifetimes of the corresponding excited states are computed. Electric dipole moments (µ) for a number of low-lying bound Λ?S states as well as several low-lying Ω-states are also calculated in the present study.     

Magnetic properties of nickel and platinum quaternary borocarbides

The zero‐field μ⁺SR technique is employed to study the magnetic properties of the non‐superconducting borocarbides Sm_1-xLu_xNi₂B₂C (x=0.0,\ 0.2) and NdPt_1.5Au_0.6B₂C. Coherent ordering of the Sm electronic moments appears below T_N=9.86(3) and 4.15(3) K for the x=0.0 and 0.2 compositions, respectively. No long range order of the Nd₃₊ moments is found in NdPt_1.5Au_0.6B₂C down to 80 mK. Freezing of the electronic moments into a spin‐glass state occurs at T_f\approx 1.2 K. A stretched exponential decay of the μ⁺ spin polarisation is observed above T_f with the exponent \beta smoothly decreasing on approaching T_f from above, reminiscent of the behaviour in other spin glasses. This revised version was published online in July 2006 with corrections to the Cover Date.