RESUMEN
We report ac susceptibility and continuous wave and pulsed EPR experiments performed on GdW10 and GdW30 polyoxometalate clusters, in which a Gd3+ ion is coordinated to different polyoxometalate moieties. Despite the isotropic character of gadolinium as a free ion, these molecules show slow magnetic relaxation at very low temperatures, characteristic of single molecule magnets. For Tâ²200 mK, the spin-lattice relaxation becomes dominated by pure quantum tunneling events, with rates that agree quantitatively with those predicted by the Prokof'ev and Stamp model [Phys. Rev. Lett. 80, 5794 (1998)]. The sign of the magnetic anisotropy, the energy level splittings, and the tunneling rates strongly depend on the molecular structure. We argue that GdW30 molecules are also promising spin qubits with a coherence figure of merit Q(M)â³50.
RESUMEN
The magnetic linear dichroism of the gadolinium 4f core level is studied in a time-resolved photoemission experiment employing laser pump- and synchrotron-radiation probe pulses. Upon optical excitation of the 5d6s valence electrons with femtosecond laser pulses, the magnetic order in the 4f spin system is reduced. Remarkably, the linear dichroism remains at 80% of the equilibrium contrast while the lattice temperature reaches the Curie temperature due to electron-phonon scattering. Contrasting itinerant ferromagnets, this shows that equilibration between the lattice and spin subsystems takes in Gd about 80 ps and is established in parallel with heat diffusion.