Studies of Ga NMR and NQR in SrGa 4
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Studies of Ga NMR and NQR in SrGa4 H. Niki · N. Higa · S. Nakamura · H. Kuroshima · T. Toji · M. Yogi · A. Nakamura · M. Hedo · T. Nakama · ¯ Y. Onuki · H. Harima
© Springer International Publishing Switzerland 2014
Abstract In order to microscopically investigate the properties in SrGa4 , the Ga NMR measurements of a powder sample were carried out. The Ga NMR spectra corresponding to Ga(I) and Ga(II) sites are obtained. The NMR spectra of 69&71 Ga (a nuclear spinI = 3/2) in the powder sample of SrGa4 do not take a typical powder pattern caused by the NQR interaction, but take the spectra consisting of three well resolved resonance-lines, which indicates that the nonuniform distribution of crystal orientation in the powder sample occurs because of the magnetic anisotropy. From the analysis of the Ga NMR spectrum, it is found that the ab-plane of the crystal is parallel to the external magnetic field, which would be attributed to the anisotropy of the magnetic susceptibility with the easy axis parallel to the ab-plane. This result is also confirmed by the 69 Ga NQR in SrGa4 . The Knight shifts of the 69 Ga(I) and 69 Ga(II) shift slightly to the negative side with decreasing temperature due to the core polarization of the d-electrons. The values of the Knight shift of the 69 Ga(I) and 69 Ga(II) are 0.01 and –0.11 % at 4.2 K, and 0.09 and –0.08 % at 300 K, respectively. The values of the 1/T1 T of the NMR of both 69 Ga(I) and 69 Ga(II) are almost constant between 4.2 and 100 K, whose values are 1.5 s−1 K−1 at 69 Ga(I) and 0.12 s−1 K−1 at 69 Ga(II), while the 1/T1 T slightly increases above 100 K with increasing temperature. The value of T1 of 69 Ga(I) is one order of magnitude less than that of 69 Ga(II). Keywords NMR · NQR · SrGa4 · Spin-lattice relaxation time · Knight shift
Proceedings of the 5th Joint International Conference on Hyperfine Interactions and International Symposium on Nuclear Quadrupole Interactions (HFI/NQI 2014) Canberra, Australia, 21–26 September 2014 H. Niki () · N. Higa · S. Nakamura · H. Kuroshima · T. Toji · M. Yogi · A. Nakamura · M. Hedo · ¯ T. Nakama · Y. Onuki Faculty of Science, University of the Ryukyus, 1 Senbaru, Nishihara, Okinawa 903-0213, Japan e-mail: [email protected] H. Harima Faculty of Science, Kobe University, Nada-ku, Kobe 657-8501, Japan
H. Niki et al.
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Fig. 1 a Crystal structure of EuGa4 . b Antiferromagnetic structure of EuGa4 . The arrows indicate the direction of magnetic moment which lies in the ab-plane
1 Introduction Strong electron correlations in rare-earth-based compounds induce various interesting physical phenomena such as heavy-electron behavior, multipole order, unconventional superconductivity, spin or valence quantum critical fluctuations, and non-Fermi liquid behavior [1–3]. Eu is a rare-earth element known to have two kinds of valence states: Eu2+ (4f 7 ) and Eu3+ (4f 6 ). The divalent Eu state is magnetic (J = S = 7/2, L = 0), where J is the total angular momentum, S is the spin angular momentum, and L is the orbital angular momentu
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