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

单分子磁体作为零维量子磁系统和潜在的量子存储应用，引起了人们的极大关注。由于SMM的主要特征是由磁各向异性势垒引起的，因此许多努力都集中在扩大SMM候选络合物的磁各向异性上。由于3d离子在自旋-轨道耦合和配位场的作用下表现出合理的各向异性，并可能演化为强的交换耦合，因此人们对3d过渡金属离子的配合物进行了大量的研究。然而，3d过渡金属离子的轨道猝灭导致了磁各向异性的极限。最近，具有大的自旋-轨道耦合和强各向异性的非猝灭轨道矩的镧系元素被建议用于改进的SMM。4f络合物的缺点之一是弱的磁交换耦合，即使提高了很大的各向异性势垒，也会导致磁化强度的快速松弛。此外，弱耦合SMM络合物在零磁场下的磁隧穿是量子存储应用的一个严重缺陷。为了克服这些问题，人们提出了3D-4F异金属配合物，因为过渡金属离子中扩展的3D轨道可以产生更强的耦合强度。然而，对于这些体系来说，用于优化磁交换和磁各向异性的磁结构关联还没有得到很好的发展。在手头的项目中，相关的磁参数，如3D-4F磁耦合和磁各向异性，将在各种3D-4F络合物上进行实验研究。主要的实验方法将是可调谐的高频/高场电子顺磁共振(EPR)谱，伴随着静态和脉冲场磁化测量。具体地说，本项目将研究合成化学基团提供的Fe2Ln2(Ln=Dy，Gd，Y)，CrDy6，Fe10Ln10(Ln=Gd，Y)，各种Co2Dy2(加上Co2Y2和Zn2Dy2)，Cu4Ln4(Ln=Dy，Y)，Ni2Ln2(Ln=Dy，Tb，Ho，Lu)和具有三角排列基团(Ln=Y，Gd，Dy)的Ln单体，以精确确定3D-4f磁相互作用的强度和磁各向异性。与Ln=Gd相比，Y提供了关于3D子系统中各向异性大小和类型以及磁相互作用的信息。与理论家的合作将产生磁-结构关联，旨在确定路线，以最大化3D和4F矩之间的交换互动。我们将制定出描述交换相互作用与络合物有效势垒之间关系的一般原理。根据有希望的配合物(如Dy6Cr)的CW-EPR结果，将研究它们的T1和T2弛豫时间，以确定它们的自旋动力学，并开发它们在量子器件中的应用潜力。

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.