Spin-lattice relaxation of individual lanthanide ions via quantum tunneling Fernando LUIS Orlando December 20 th 2010 Quantum Coherent Properties of Spins-III Workshop
Spin-lattice relaxation T Spin ensemble Thermal bath (phonons) Spin-lattice interaction h P. Curie P. Ehrenfest (1892)(1919) P. Curie, Comptes Rendus Acad. Sci. (France) (1892) P. Ehrenfest, Leiden Commun. Suppl. 4b (1919).
Phonon emission and absorption Equilibrium E cb E ba Kronig, R. de L., Physica 6, 33 (1939). Van Vleck, J. H., Phys. Rev. 57, 426 (1940). R. Orbach, Proc. Roy. Soc. (London) A264, 456 (1961) Orbach Direct 1/ (s -1 ) 1/T (K -1 )
Phonon emission and absorption Equilibrium E cb E ba Van Vleck (1940) Kronig, R. de L., Physica 6, 33 (1939). Van Vleck, J. H., Phys. Rev. 57, 426 (1940). R. Orbach, Proc. Roy. Soc. (London) A264, 456 (1961)
Mononuclear single-molecule magnets LnW 10 LnW 30 Lanthanide (Er, Ho, Gd, Tm…) Polyoxometalate moiety Some outstanding characteristics… Simple (just 1 magnetic atom) Weak interactions Magnetic solubility Nuclear-spin free systems Control over parameters M. A. AlDamen et al, J. Am. Chem. Soc. 130, 8874 (2008) 17.9 Å
Tailoring the magnetic anisotropy by chemistry: the case of Gd GdW 10 GdW 30 Gd: [Xe]4f 7 L = 0, S = 7/2 ? Model crystal-field probe
GdW 10 S = 7/2 g = 2 GdW 30 S = 7/2 g = 2
GdW 10 S = 7/2 g = 2 GdW 30 S = 7/2 g = 2 B 20 /k B = K B 44 /k B 4 K B 20 /k B = K B 22 /k B K
Easy axis JzJz /k B = K /k B = K JyJy Easy plane 4 K 0.5 K
M. J. Martíınez-Pérez, J. Sesé, F. Luis, D. Drung, T. Schurig, Rev. Sci. Instrum. 81, (2010). GdW 10 GdW 30
Long-range magnetic order: T N 20 mK dip /k B 0.02 K Above T N, T follows Curie-Weiss law is a SLR time
T > 0.1 K: Thermally activated Agrees with Orbach process 10 9 T < 0.1 K: Independent of T 8-9 orders of magnitude faster than direct processes
J = 15/2 g = 6/5 ~ 45 K B 20 /k B = K; B 40 /k B = K; B 60 /k B = 1.67 K B 44 /k B 1.8 K Strong uniaxial anisotropy Spin-lattice relaxation and quantum tunneling the case of Er ErW 10 SMM behaviour below 5 K AF order at T N = 80 mK M. Aldamen et al., Inorg. Chem. 48, 3467 (2009) F. Luis et al., Phys Rev. B 82, (R) (2010)
10 9 F. Luis et al., Phys Rev. B 82, (R) (2010)
What about tunneling then? /k B K dip 0.08 K Tunneling Direct process N. V. Prokof’ev and P. C. E. Stamp, Phys. Rev. Lett. 80, 5794 (1998).
Effect of a magnetic field dip = - Zeeman Zeeman
Effect of a magnetic field dip = - Zeeman Zeeman Direct process
Spin concentration Er x Y 1-x W 10 Er Y
Er 3+ : Kramers ion (J = 15/2) = 0 at zero field H dipx are required to break Kramers degeneracy Increasing dipx x x dip x tun x tun x 2
Hyperfine interactions 167 ErW 10 I = Er, 166 Er 168 Er, 170 Er I = 7/2 A/k B = -6 K 167 Er 0
Hyperfine interactions 167 ErW 10 dip = - hyperfine
Strong hyperfine interactions HoW 10 (1) (2)
T > T N T < T N dip >> Relaxation vs long-range order: ErW 10 T N = 81 mK The onset of long-range order blocks QT and relaxation
Aging: monitoring the growth of spin-spin correlations time t 1 t 2 t 3
T Spin ensemble Thermal bath (phonons) -1 QT spin reversal vs spin lattice relaxation QT flips the spins but conserves energy of the spin ensemble How is energy exchanged with the thermal bath then?
Zeeman bath Dipolar bath Phonon bath dir tun SR Collective emission of phonons: phonon superradiance H. N. V. Temperley, Proc. Camb. Phil. Soc. 35, 256 (1939). E. M. Chudnovsky and D. A. Garanin, Phys. Rev. Lett. 93, (2004).
Conclusions Mononuclear SMM: tailoring the energy level structure with chemistry magnetic coolers, qubits, … Nearly quantitative agreement between measured tunneling rates and theory Quantum spin tunneling provides a very efficient mechanism of spin-lattice relaxation Puzzle: energy flow between spins and the lattice ?
Javier Sesé Mª José Martínez David Zueco Agustín Camon Marco Evangelisti Oscar Montero Enrique Burzurí Thomas Schurig Dietmar Drung Salvador Cardona- Serra Carlos Martí-Gastaldo Juan Modesto Clemente Eugenio Coronado Joris van Slageren Christoph Schlegel