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Thulium

169 Tm Mössbauer Spectroscopy J.M. Cadogan Department of Physics and Astronomy University of Manitoba Winnipeg, Manitoba, R3T 2N2 Canada E-mail: cadogan@physics.umanitoba.ca. Thulium. Thulium is a Lanthanide metal (“Rare-Earth”) with an atomic number of 69.

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Thulium

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  1. 169Tm Mössbauer SpectroscopyJ.M. CadoganDepartment of Physics and AstronomyUniversity of ManitobaWinnipeg, Manitoba, R3T 2N2CanadaE-mail: cadogan@physics.umanitoba.ca

  2. Thulium • Thulium is a Lanthanide metal (“Rare-Earth”) with an atomic number of 69. • Tm3+ has an outer electronic configuration of 4f12 and an electronic ground-state 3H6 (J=6, L=5, S=1) • The “free-ion” magnetic moment of Tm3+ is 7 mB.

  3. Experimental • The 169Tm source is made by neutron irradiation of 168Er • The intrinsic 169Tm linewidth is about 25 times larger than that of 57Fe. • The low recoil energy of 169Tm allows measurements up to ~ 1000 K.

  4. 169Tm: comparison with 57Fe

  5. The 169Tm Mössbauer transition is a 3/2 → 1/2 transition, the same as that of 57Fe. However, the energy splittings are 2 orders of magnitude larger.

  6. Some examples of 169Tm Mössbauer studies • Tm2Ge2O7 (5-fold symmetry ?) • TmFe2 (crystal-field effects and magnetic order) • Tm3Al2 &Tm2Al (exceptionally slow electronic relaxation)

  7. Tm2Ge2O7 • Thulium pyrogermanate (TmPG) is tetragonal P41212 • The Tm3+ site (8b) has triclinic symmetry and is coordinated by 7 O2− ions, forming a distorted pentagonal bipyramid • The Tm3+ triclinic crystal-field hamiltonian contains 27 terms. A pentagonal hamiltonian has only 5 terms (an obvious mathematical advantage) ! • Can the Tm3+ magnetism be described using 5-fold symmetry ? (A triclinic symmetry yields 13 non-magnetic singlets whereas a 5-fold symmetry permits 5 magnetic doublets and 3 non-magnetic singlets)

  8. 169Tm Mössbauer spectra of TmPG The 169Tm Mössbauer spectra of TmPG are broad quadrupole-split doublets. The temperature dependence of the quadrupole splitting can be fitted in terms of the Tm3+ crystal field Hamiltonian. Triclinic symmetry model QS (mm/s) 5-fold model Rel. Transmission (%) T(K) G. A. Stewart, J.M. Cadogan and A.V.J. Edge, J. Phys. Condensed Matter, 4, 1849-58 (1992) v (mm/s)

  9. 169Tm Mössbauer spectra of TmFe2 TmFe2 is a cubic Laves phase compound.The 169Tm Mössbauer spectra of TmFe2 are magnetically-split sextets corresponding to very large hyperfine fields (720 T at 1.3 K). Note the velocity scale: ± 700 mm/s. For comparison, the magnetic splitting of a-Fe (a standard calibration material for 57Fe work) is ± 5.3 mm/s – about the size of two dots on this picture ! Rel. Transmission (%) B. Bleaney, G.J. Bowden, J.M. Cadogan, R.K. Day and J.B. Dunlop. J. Phys. F: Metal Physics, 12, 795-811 (1982) v (mm/s)

  10. 169Tm Mössbauer spectra of TmFe2 The temperature dependences of the magnetic hyperfine field and the electric quadrupole splitting at the 169Tm nucleus can be fitted to yield the crystal-field and exchange parameters describing the magnetism of the Tm3+ ion. Reduced Quadrupole splitting Bhf (T) T(K) T(K) B. Bleaney, G.J. Bowden, J.M. Cadogan, R.K. Day and J.B. Dunlop. J. Phys. F: Metal Physics, 12, 795-811 (1982)

  11. 169Tm Mössbauer spectra of Tm3Al2Slow electronic relaxation Tm3Al2 is tetragonal (P42nm) with 3 Tm sites. The antiferromagnetic ordering temperature is 6 K. 169Tm Mössbauer spectroscopy shows a fully magnetically split sextet even up to 45 K, indicative of unusually slow electronic relaxation. 11.6 K 4.2 K 1.3 K 45 K 30 K 18 K Rel. Transmission (%) v (mm/s) v (mm/s) G.J. Bowden, J.M. Cadogan, R.K. Day and J.B. Dunlop. J. Phys. F: Metal Physics, 11, 503-510 (1981): Hyp Int., 39, 359-67 (1988)

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