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- ItemTuning the spin coherence time of Cu(II)−(bis)oxamato and Cu(II)−(bis)oxamidato complexes by advanced ESR pulse protocols(Frankfurt, M. : Beilstein-Institut zur Förderung der Chemischen Wissenschaften, 2017-4-27) Zaripov, Ruslan; Vavilova, Evgeniya; Khairuzhdinov, Iskander; Salikhov, Kev; Voronkova, Violeta; Abdulmalic, Mohammad A.; Meva, Francois E.; Weheabby, Saddam; Rüffer, Tobias; Büchner, Bernd; Kataev, VladislavWe 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 Tm 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-Pr24– 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 Tm times. Such a detrimental effect of the opbon-Pr24− 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.
- ItemProbing the magnetic superexchange couplings between terminal CuII ions in heterotrinuclear bis(oxamidato) type complexes(Frankfurt, M. : Beilstein-Institut zur Förderung der Chemischen Wissenschaften, 2017-4-6) Abdulmalic, Mohammad A.; Weheabby, Saddam; Meva, Francois E.; Aliabadi, Azar; Kataev, Vladislav; Büchner, Bernd; Schleife, Frederik; Kersting, Berthold; Rüffer, TobiasThe reaction of one equivalent of [n-Bu4N]2[Ni(opboR2)] with two equivalents of [Cu(pmdta)(X)2] afforded the heterotrinuclear CuIINiIICuII containing bis(oxamidato) type complexes [Cu2Ni(opboR2)(pmdta)2]X2 (R = Me, X = NO3– (1); R = Et, X = ClO4– (2); R = n-Pr, X = NO3– (3); opboR2 = o-phenylenebis(NR-substituted oxamidato); pmdta = N,N,N’,N”,N”-pentamethyldiethylenetriamine). The identities of the heterotrinuclear complexes 1–3 were established by IR spectroscopy, elemental analysis and single-crystal X-ray diffraction studies, which revealed the cationic complex fragments [Cu2Ni(opboR2)(pmdta)2]2+ as not involved in any further intermolecular interactions. As a consequence thereof, the complexes 1–3 possess terminal paramagnetic [Cu(pmdta)]2+ fragments separated by [NiII(opboR2)]2– bridging units representing diamagnetic SNi = 0 states. The magnetic field dependence of the magnetization M(H) of 1–3 at T = 1.8 K has been determined and is shown to be highly reproducible with the Brillouin function for an ideal paramagnetic spin = 1/2 system, verifying experimentally that no magnetic superexchange couplings exists between the terminal paramagnetic [Cu(pmdta)]2+ fragments. Susceptibility measurements versus temperature of 1–3 between 1.8–300 K were performed to reinforce the statement of the absence of magnetic superexchange couplings in these three heterotrinuclear complexes.
- ItemOrbital reconstruction in nonpolar tetravalent transition-metal oxide layers(London : Nature Publishing Group, 2015) Bogdanov, Nikolay A.; Katukuri, Vamshi M.; Romhányi, Judit; Yushankhai, Viktor; Kataev, Vladislav; Büchner, Bernd; van den Brink, Jeroen; Hozoi, LiviuA promising route to tailoring the electronic properties of quantum materials and devices rests on the idea of orbital engineering in multilayered oxide heterostructures. Here we show that the interplay of interlayer charge imbalance and ligand distortions provides a knob for tuning the sequence of electronic levels even in intrinsically stacked oxides. We resolve in this regard the d-level structure of layered Sr2IrO4 by electron spin resonance. While canonical ligand-field theory predicts g
- ItemInsights into the Spin–Orbital Entanglement in Complex Iridium Oxides from High-Field ESR Spectroscopy(Wien [u.a.] : Springer, 2021) Kataev, VladislavComplex iridium oxides have attracted recently a substantial interdisciplinary attention due to an intimate entanglement of spin and orbital degrees of freedom which may give rise to a novel spin–orbital Mott insulating behavior and exotic quantum spin liquid phases. Electron spin resonance (ESR) spectroscopy is known to be an instructive tool for studying the spin–orbital coupling (SOC) effects as it can directly access the relevant parameters sensitive to SOC, such as the g factor tensor, magnetic anisotropy gaps and spin dynamics. In this article, a systematic study at the Leibniz IFW Dresden of the static and dynamic properties of selected Ir-based materials with multi-frequency high-field ESR spectroscopy will be reviewed. Specifically, evidence for a surprisingly isotropic antiferromagnetic spin dynamics and the inversion of the orbital states in the prototypical spin–orbital Mott insulator Sr 2IrO 4, observation of the collective resonance modes in the family of double perovskites La 2BIrO 6 (B = Cu, Co) and the origin of the unexpected magnetism in the double perovskite Ba 2YIrO 6 will be highlighted. © 2021, The Author(s).