Experimental studies on magnetic interaction and anisotropy in 3d-4f heterometallic systems

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Single molecular magnets (SMMs) attract lots of attention as zero-dimensional quantum magnetic systems and potential candidates for quantum storage applications. Since the main characteristic of SMMs is induced by the magnetic anisotropy barrier, many efforts focus on the enlargement of magnetic anisotropy of the SMM candidate complexes. So far many complexes involving 3d transition metal ions have been studied because 3d ions show a reasonable anisotropy induced by spin-orbit coupling and ligand field, and they may evolve strong exchange coupling. However, orbital quenching in 3d transition metal ions causes a limit of magnetic anisotropy. Recently, lanthanides where unquenched orbital moments provide large spin-orbit coupling and strong anisotropy have been suggested for improved SMMs. One of the disadvantages of 4f complexes is weak magnetic exchange coupling which induces fast relaxation of magnetization even though large anisotropy barrier is raised. Moreover, magnetic tunneling at zero-magnetic field in weakly coupled SMM complexes is a critical deficient for quantum storage applications. In order to overcome these issues, 3d-4f heterometallic complexes are suggested as the extended 3d orbitals in transition metal ions can yield enhanced coupling strengths. However, for these systems magneto-structural correlations for optimizing magnetic exchange and magnetic anisotropy are not yet well developed. In the project at hand, relevant magnetic parameters, such as 3d-4f magnetic coupling and magnetic anisotropy, will be experimentally studied on a variety of 3d-4f complexes. The main experimental method will be tunable high-frequency/high-field electron paramagnetic resonance (EPR) spectroscopy which will be accompanied by static and pulsed field magnetization measurements. To be specific, Fe2Ln2 (Ln = Dy, Gd, Y), CrDy6, Fe10Ln10 (Ln = Gd, Y), various Co2Dy2 (plus Co2Y2 and Zn2Dy2), Cu4Ln4 (Ln = Dy, Y), Ni2Ln2 (Ln = Dy, Tb, Ho, Lu) and Ln monomers with triangular arranged radicals (Ln = Y, Gd, Dy) provided by synthetic chemistry groups for this project will be studied in order to precisely determine the strength of 3d-4f magnetic interaction as well as magnetic anisotropy. Comparison with Ln = Gd,Y provides information on the anisotropy size and type and on magnetic interaction in the 3d-subsystems. Collaboration with theorists will yield magneto-structural correlations, aiming at determining routes to maximize the exchange interaction between 3d and 4f moments. We will work out general principles describing the relation between the exchange interaction and effective barrier of the complexes. Depending on the cw-EPR results of promising complexes (e.g. Dy6Cr) T1- and T2-relaxation times will be studied in order to determine their spin dynamics and to exploit their potential for quantum device applications.