Electric field gradients in MgB2 synthesized at high pressure: 111Cd TDPAC study and ab initio calculation

Tsvyashchenko, A. V.; Фомичева, Л.Н.; Magnitskaya, M. V.; Shirani, Ebrahim; Brudanin, V.; Filossofov, D.V.; Kochetov, O.; Lebedev, N.A.; Novgorodov, A.F.; Salamatin, A. V.; Korolev, Nikolay; Velichkov, A.; Timkin, V.; Менушенков, А. П.; Kuznetsov, A. V.; Shabanov, V.M.; Akselrod, Z. Z.

doi:10.1016/s0038-1098(01)00229-0

Cited by 16 publications

(23 citation statements)

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“…Finally there is also a report [6] of a negative 11 B shift of mere 5 ppm attributed to the core polarization. These large discrepancies most likely come from the choice of * Electronic address: mali@physik.unizh.ch different materials as references for the Knight shift, as well as from difficulties to measure the small 11 B Knight shift of a broad and in addition quadrupolarly shifted 11 B central line powder spectrum.As far as we know, there are no experimental data concerning the NMR quantities at the Mg site in MgB 2 , although theoretical predictions based on ab initio local density approximation (LDA) calculations exist for Mg Knight shift, 1/T 1 and EFG [7,8]. To some degree the lack of experimental Mg NMR data is understandable considering the fact that the only NMR active 25 Mg isotope has a small magnetic moment and low natural abundance.…”

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confidence: 99%

“…As far as we know, there are no experimental data concerning the NMR quantities at the Mg site in MgB 2 , although theoretical predictions based on ab initio local density approximation (LDA) calculations exist for Mg Knight shift, 1/T 1 and EFG [7,8]. To some degree the lack of experimental Mg NMR data is understandable considering the fact that the only NMR active 25 Mg isotope has a small magnetic moment and low natural abundance.…”

mentioning

confidence: 99%

“…As far as we know, there are no experimental data concerning the NMR quantities at the Mg site in MgB 2 , although theoretical predictions based on ab initio local density approximation (LDA) calculations exist for Mg Knight shift, 1/T 1 and EFG [7,8] The MgB 2 sample was prepared using stoichiometric amounts of magnesium and boron (99% and 99.99%, respectively) in a form of powder. Both components were thoroughly mixed and pressed into pellets.…”

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25MgNMR study of theMgB2superconductor

et al. 2002

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25 Mg NMR spectra and nuclear spin-lattice relaxation time, T1, have been measured in polycrystalline MgB2 with a superconducting transition temperature Tc = 39 K in zero magnetic field. From the first order and second order quadrupole perturbed NMR spectrum a quadrupole coupling frequency νQ = 222.0(1.5) kHz is obtained. T1T = 1090(50) sK and Knight shift Kc = 242(4) ppm are temperature independent in the normal conducting phase. The 25 Mg Korringa ratio equals to 0.95 which is very close to the ideal value of unity for s-electrons. The comparison of the experimental νQ, T1T , and Kc with the corresponding values obtained by LDA calculations shows an excellent agreement for all three quantities.PACS numbers: 74.70. Ad, 74.25.Jb, 74.25.Nf, 76.60.Cq, The recent discovery of superconductivity in MgB 2 with remarkably high T c = 39 K [1] has attracted much attention. In particular the observation of a sizeable boron [2] isotope effect strongly suggests that this simple layered intermetallic compound belongs to the conventional family of phonon mediated BCS superconductors. The relevant electron-phonon coupling constant is proportional to the density of states (DOS) at the Fermi level. So it is important to have experimental data of this quantity in MgB 2 .Nuclear magnetic resonance (NMR) in metals probes the DOS at the Fermi level. The measured quantities, the spin lattice relaxation rate, 1/T 1 , and the Knight shift, K, are related to the electron spin susceptibility (χ(q, ω)) of electrons close to the Fermi level, specifically 1/(T 1 T ) ∝ lim ω→0 q Imχ(q, ω)/ω, and K ∝ Reχ(0, 0). In case the atomic site symmetry in the crystal structure is less than cubic and the atom has a nuclear quadrupole moment as it applies for Mg and B in MgB 2 , quadrupolar disturbed NMR delivers in addition valuable information on the electric field gradient (EFG) at the specific nuclear site. Unlike 1/T 1 and K the EFG is determined by the distribution of all charges. Up to date only measurements of 1/T 1 , K, and of the quadrupole coupling to the EFG, expressed by quadrupole coupling frequency ν Q , of 11 B were performed [3,4,5,6]. While there is reasonable agreement among 11 B ν Q 's and relaxation rates, there is a considerable controversy concerning the 11 B Knight shifts. While some authors [4] report in the normal conducting state a small temperature independent isotropic shift of 175 ppm, others [5] report a smaller and even temperature dependent shift of approximately 60 ppm, which they attribute to the Fermi-contact interaction. Finally there is also a report [6] of a negative 11 B shift of mere 5 ppm attributed to the core polarization. These large discrepancies most likely come from the choice of * Electronic address: mali@physik.unizh.ch different materials as references for the Knight shift, as well as from difficulties to measure the small 11 B Knight shift of a broad and in addition quadrupolarly shifted 11 B central line powder spectrum.As far as we know, there are no experimental data concerning the NMR quantities at...

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mentioning

confidence: 99%

“…As far as we know, there are no experimental data concerning the NMR quantities at the Mg site in MgB 2 , although theoretical predictions based on ab initio local density approximation (LDA) calculations exist for Mg Knight shift, 1/T 1 and EFG [7,8] The MgB 2 sample was prepared using stoichiometric amounts of magnesium and boron (99% and 99.99%, respectively) in a form of powder. Both components were thoroughly mixed and pressed into pellets.…”

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25MgNMR study of theMgB2superconductor

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“…27͒ and −3.2 V / Å. 8 In order to investigate the effect of the cell parameters on the calculated EFG, the calculations were repeated with the optimized lattice constants at PW91 level, a = 3.090 Å, and c = 3.584 Å. The difference of calculated EFG with experimental and optimized lattice parameters was smaller than 0.1 V / Å 2 .…”

Section: Quantum Chemical Calculationsmentioning

confidence: 99%

“…5 Band structure calculations have shown that Mg atoms are substantially ionized and that the bands at the Fermi level derive mainly from B orbitals. [6][7][8] Hitherto conventional nuclear magnetic resonance ͑NMR͒ studies have been performed on 11 B ͑Refs. 9-13͒ and 25 Mg ͑Refs.…”

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confidence: 99%

Local electronic structure inMgB2fromB12
Indris
¹
,
Heitjans
²
,
Hattendorf³
et al. 2007
Phys. Rev. B

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We performed ␤-NMR spectroscopic studies on 12 B which was implanted into MgB 2 to get insight into the local electronic structure of this high-temperature superconducting material. By measuring electric field gradients we probed the electronic charge distribution anisotropy around boron in this solid and thus obtained experimental information about the bonding by p electrons. Besides the absolute value, the sign of the electric field gradient was also experimentally determined. By comparison with quantum chemical calculations, some of which were performed in the present work, and with results from conventional NMR spectroscopy on 11 B we were able to identify regular boron lattice sites as well as interstitial sites.

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Recent Advances in Solid-State 25Mg NMR Spectroscopy

Freitas

Smith

2012

Annual Reports on NMR Spectroscopy

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Electric field gradients in MgB2 synthesized at high pressure: 111Cd TDPAC study and ab initio calculation

Cited by 16 publications

References 23 publications

25MgNMR study of theMgB2superconductor

25MgNMR study of theMgB2superconductor

Local electronic structure inMgB2fromB12
Indris
¹
,
Heitjans
²
,
Hattendorf³
et al. 2007
Phys. Rev. B

Recent Advances in Solid-State 25Mg NMR Spectroscopy

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Electric field gradients in MgB2 synthesized at high pressure: 111Cd TDPAC study and ab initio calculation

Cited by 16 publications

References 23 publications

25MgNMR study of theMgB2superconductor

25MgNMR study of theMgB2superconductor

Local electronic structure inMgB2fromB12Indris1, Heitjans2, Hattendorf3 et al. 2007Phys. Rev. B

Recent Advances in Solid-State 25Mg NMR Spectroscopy

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About

Local electronic structure inMgB2fromB12
Indris
¹
,
Heitjans
²
,
Hattendorf³
et al. 2007
Phys. Rev. B