Unusual properties of the molecular nanomagnet Mn12ac

Abstract

Articles you may be interested inSlow magnetic relaxation and electron delocalization in an S = 9/2 iron(II/III) complex with two crystallographically inequivalent iron sites Resonant magnetic quantum tunneling through thermally activated states Thermally assisted macroscopic quantum resonance on a single-crystal of Mn 12 -acetateThe magnetic properties of the Mn 12 ac molecular cluster were studied by complex susceptibility and specific heat measurements. Extensive ac susceptibility measurements done under a magnetic field on good quality single crystals and zero field powder sample specific heat results indicate that the usual uniaxial Hamiltonian, as well as the recently proposed fourth order corrections, are not enough to account for all the observations. Very low temperature specific heat data indicate the presence of zero field splitting of the ground state which is much larger than expected. Finally, specific heat measurements done under a magnetic field permitted us to observe and measure the lattice spin relaxation by calorimetric methods with time constants that are in agreement with the magnetic relaxation measurements.

Measurement of the Relaxation Rate of the Magnetization inMn12O12-Acetate Using Proton NMR Echo

“…(1) as a function of temperature at 0.45 T are compared in Fig. 2 with the results obtained in Mn12 from magnetization [6] and specific heat [27] measurements. The NMR set of data shows little scatter and is in good agreement with the measurements obtained at approximately the same field H with the SQUID, confirming that we have a new microscopic method to study the relaxation of magnetization in molecular clusters.…”

Calorimetric Investigation of Phase Transitions Occurring in Molecule-Based Magnets

“…The temperature dependence of heat capacity of several Mn12 compounds was reported for polycrystalline samples − and for single crystals. − In several works, clear heat-capacity drops at T B were observed by application of magnetic field. ,, Because the dipolar fields exerted from neighboring molecules are also effective to remove the degeneracy of the ground doublet, the heat capacity under zero external field was closely examined to obtain the information on the freezing process . The results showed lowering of the T B and the blocking process over a certain temperature range.…”

Magnetic-Field-Dependent Heat Capacity of the Single-Molecule Magnet [Mn12O12(O2CEt)16(H2O)3]

“…Similar thermal anomalies were also found in Mn 12 Ac. 18,23 We shall discuss the origin of these thermal anomalies later.…”

“…The heat capacity due to the hyperfine interaction of the Mn nuclei C hf was actually observed in Mn 12 -Ac. 18,23 In the case of Mn 12 Pr, C hf is remarkably below 0.5 K. In the analysis of the results below 5 K in a zero magnetic field using eq 3, it was revealed that two kinds of spin clusters characterized by different D values should be incorporated into the model. This just corresponds to the Jahn-Teller isomers mentioned previously.…”

“…Whenever the magnetic field fulfills the condition of B ) nD/ gµ B (n being an integer), two Zeeman splitting energy levels belonging to different m s states coincide, and the QTM may occur. 13,14 Calorimetric 15-23 and magnetic 13,14,17,18,[24][25][26][27][28][29] studies hitherto done for single-molecule magnets fundamentally support the validity of the QTM mechanism. However, such studies have mostly addressed Mn 12 Ac and [Fe 8 O 2 (OH) 12 (tacn) 6 ]Br 8 ‚9H 2 O (tacn ) triazacyclononane).…”