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Identification of the Chromophore in the Apatite Pigment [Sr 10 (PO 4 ) 6 (Cu x OH 1− x − y ) 2 ]: Linear OCuO − Featuring a Resonance Raman Effect, an Extreme Magnetic Anisotropy, and Slow Spin Relaxation
Author(s) -
Kazin Pavel E.,
Zykin Mikhail A.,
Zubavichus Yan V.,
Magdysyuk Oxana V.,
Dinnebier Robert E.,
Jansen Martin
Publication year - 2014
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201303136
Subject(s) - magnetization , paramagnetism , relaxation (psychology) , chemistry , diamagnetism , analytical chemistry (journal) , raman spectroscopy , crystallography , materials science , nuclear magnetic resonance , condensed matter physics , magnetic field , psychology , social psychology , physics , chromatography , quantum mechanics , optics
A new chromophore has been identified in copper‐doped apatite pigments having the general composition [Sr 10 (PO 4 ) 6 (Cu x OH 1− x − y ) 2 ], in which x =0.1, 0.3 and y =0.01–0.42. By using X‐ray absorption spectroscopy, low‐temperature magnetization measurements, and synchrotron X‐ray powder structure refinement, it has been shown that the oxygenated compounds contain simultaneously diamagnetic Cu 1+ and paramagnetic Cu 3+ with S =1. Cu 3+ is located at the same crystallographic position as Cu 1+ , being linearly coordinated by two oxygen atoms and forming the OCuO − anion. The Raman spectroscopy study of [A 10 (PO 4 ) 6 (Cu x OH 1− x − y ) 2 ,], in which A=Ca, Sr, Ba, reveals resonance bands at 651–656 cm −1 assigned to the symmetric stretching vibration ( ν 1 ) of OCuO − . The strontium apatite pigment exhibits a strong paramagnetic anisotropy with an unprecedentedly large negative zero‐field splitting parameter ( D ) of ≈−400 cm −1 . The extreme magnetic anisotropy causes slow magnetization relaxation with relaxation times ( τ ) up to 0.3 s at T =2 K, which relates the compounds to single‐ion magnets. At low temperature, τ is limited by a spin quantum‐tunneling, whereas at high temperature a thermally activated relaxation prevails with U eff ≈48 cm −1 . Strong dependence of τ on the paramagnetic center concentration at low temperature suggests that the spin‐spin relaxation dominates in the spin quantum‐tunneling process. The compound is the first example of a d‐metal‐based single‐ion magnet with S =1, the smallest spin at which an energy barrier arises for the spin flipping.