Tuning the spin coherence time of Cu(II)−(bis)oxamato and Cu(II)−(bis)oxamidato complexes by advanced ESR pulse protocols

Abstract

We have investigated with the pulsed ESR technique at X- and Q-band frequencies the coherence and relaxation of Cu spins S = 1/2 in single crystals of diamagnetically diluted mononuclear [n-Bu4N]2[Cu(opba)] (1%) in the host lattice of [n-Bu4N]2[Ni(opba)] (99%, opba = o-phenylenebis(oxamato)) and of diamagnetically diluted mononuclear [n-Bu4N]2[Cu(opbon-Pr2)] (1%) in the host lattice of [n-Bu4N]2[Ni(opbon-Pr2)] (99%, opbon-Pr2 = o-phenylenebis(N(propyl)oxamidato)). For that we have measured the electron spin dephasing time T m at different temperatures with the two-pulse primary echo and with the special Carr–Purcell–Meiboom–Gill (CPMG) multiple microwave pulse sequence. Application of the CPMG protocol has led to a substantial increase of the spin coherence lifetime in both complexes as compared to the primary echo results. It shows the efficiency of the suppression of the electron spin decoherence channel in the studied complexes arising due to spectral diffusion induced by a random modulation of the hyperfine interaction with the nuclear spins. We argue that this method can be used as a test for the relevance of the spectral diffusion for the electron spin decoherence. Our results have revealed a prominent role of the opba4– and opbon-Pr2 4– ligands for the dephasing of the Cu spins. The presence of additional 14N nuclei and protons in [Cu(opbon-Pr2)]2– as compared to [Cu(opba)]2– yields significantly shorter T m times. Such a detrimental effect of the opbon-Pr2 4− ligands has to be considered when discussing a potential application of the Cu(II)−(bis)oxamato and Cu(II)−(bis)oxamidato complexes as building blocks of more complex molecular structures in prototype spintronic devices. Furthermore, in our work we propose an improved CPMG pulse protocol that enables elimination of unwanted echoes that inevitably appear in the case of inhomogeneously broadened ESR spectra due to the selective excitation of electron spins.

Coherent spin dynamics of solitons in the organic spin chain compounds(o-DMTTF)2X(X=Cl,Br)

“…It is worthwhile mentioning that, within the temperature range of our CPMG investigation between 3.6 and 16 K, the strength of deviations of the CPMG decay curves from a monoexponential behavior increase with decreasing temperature. This could point towards a temperature-dependence of the spin decoherence mechanism, for instance by virtue of temperature dependent spin-lattice relaxation of the (electron or nuclear) spins [35,36]. In conclusion, it is possible to effectively enhance the spin coherence of the solitons in (o -DMTTF) 2 Br by applying a CPMG pulse sequence.…”

“…Such an enhancement has been theoretically predicted and experimentally observed, for instance, in molecular magnets (see, e.g., Refs. [35,36] and references therein) and was attributed to contributions of certain spectral diffusion processes, caused by a stochastic modulation of the hyperfine interactions, to the decoherence of the spins which are strongly suppressed by the CPMG pulse sequence. In this case, however, the shape of the relaxation curves of the spin echoes is expected to be converted from a stretched-exponential behavior in the case of the primary echo method towards a monoexponential decay in the case of CPMG measurements [36].…”

When Molecular Magnetism Meets Supramolecular Chemistry: Multifunctional and Multiresponsive Dicopper(II) Metallacyclophanes as Proof-of-Concept for Single-Molecule Spintronics and Quantum Computing Technologies?

“…One further step in this area will be the use of oxamato-based dicopper(II) metallacyclophanes as basic logic units (quantum gates) for the future generation of quantum computers (Figure 9b). The recent work by Rüffer and Kataev on the quantum coherence (QC) properties of related mononuclear oxamato-containing copper(II) complexes is particularly encouraging, as it shows that sufficiently long spin coherence times for quantum gate operations can be achieved in these simple systems [178]. However, this is not an easy task because it implies the rational design of very weakly interacting ("entangled") and potentially switchable molecules before applications could be envisaged, as illustrated by the impressive work of Winpenny on supramolecular arrays of metal rings [75][76][77][78][79].…”

The interplay between spin densities and magnetic superexchange interactions: case studies of mono- and trinuclear bis(oxamato)-type complexes

“…This presentation of our results should not end without reference to further studies of such diamagnetically diluted single crystals. We have recently shown the means of manipulating and enhancing the electron spin coherence of 2@1 and 10@9 at different temperatures by applying special microwave pulse sequences in an ESR experiment [ 51 ]. We aim to obtain with such experiments further insights into an understanding of mononuclear type- II and bis(oxamidato) complexes with respect to their electron spin dynamics, spin coherence and relaxation processes as well as their possible applications in molecular electronic devices.…”