Macroscopic measurement of resonant magnetization tunneling in high-spin molecules
TL;DR: It is proposed that these effects are manifestations of thermally assisted, field-tuned resonant tunneling between quantum spin states, and attribute the observation of quantum-mechanical phenomena on a macroscopic scale to tunneling in a large (Avogadro's) number of magnetically identical molecules.
Abstract: We report the observation of steps at regular intervals of magnetic field in the hysteresis loop of a macroscopic sample of oriented M${\mathrm{n}}_{12}$${\mathrm{O}}_{12}$(C${\mathrm{H}}_{3}$COO${)}_{16}$(${\mathrm{H}}_{2}$O${)}_{4}$ crystals. The magnetic relaxation rate increases substantially when the field is tuned to a step. We propose that these effects are manifestations of thermally assisted, field-tuned resonant tunneling between quantum spin states, and attribute the observation of quantum-mechanical phenomena on a macroscopic scale to tunneling in a large (Avogadro's) number of magnetically identical molecules.
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TL;DR: This work reviews the first progress in the resulting field, molecular spintronics, which will enable the manipulation of spin and charges in electronic devices containing one or more molecules, and discusses the advantages over more conventional materials, and the potential applications in information storage and processing.
Abstract: A revolution in electronics is in view, with the contemporary evolution of the two novel disciplines of spintronics and molecular electronics. A fundamental link between these two fields can be established using molecular magnetic materials and, in particular, single-molecule magnets. Here, we review the first progress in the resulting field, molecular spintronics, which will enable the manipulation of spin and charges in electronic devices containing one or more molecules. We discuss the advantages over more conventional materials, and the potential applications in information storage and processing. We also outline current challenges in the field, and propose convenient schemes to overcome them.
2,694 citations
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...Moreover, their molecular nature leads to appealing quantum effects of the static and dynamic magnetic propertie...
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TL;DR: In this article, an implementation of Grover's algorithm that uses molecular magnets was proposed, which can be used to build dense and efficient memory devices based on the Grover algorithm, in which one single crystal can serve as a storage unit of a dynamic random access memory device.
Abstract: Shor and Grover demonstrated that a quantum computer can outperform any classical computer in factoring numbers1 and in searching a database2 by exploiting the parallelism of quantum mechanics. Whereas Shor's algorithm requires both superposition and entanglement of a many-particle system3, the superposition of single-particle quantum states is sufficient for Grover's algorithm4. Recently, the latter has been successfully implemented5 using Rydberg atoms. Here we propose an implementation of Grover's algorithm that uses molecular magnets6,7,8,9,10, which are solid-state systems with a large spin; their spin eigenstates make them natural candidates for single-particle systems. We show theoretically that molecular magnets can be used to build dense and efficient memory devices based on the Grover algorithm. In particular, one single crystal can serve as a storage unit of a dynamic random access memory device. Fast electron spin resonance pulses can be used to decode and read out stored numbers of up to 105, with access times as short as 10-10 seconds. We show that our proposal should be feasible using the molecular magnets Fe8 and Mn12.
2,378 citations
TL;DR: Double-decker phthalocyanine complexes with Tb3+ or Dy3+ showed slow magnetization relaxation as a single-molecular property and a significant temperature rise results from a mechanism in the relaxation process different from that in the transition-metal-cluster SMMs.
Abstract: Double-decker phthalocyanine complexes with Tb3+ or Dy3+ showed slow magnetization relaxation as a single-molecular property. The temperature ranges in which the behavior was observed were far higher than that of the transition-metal-cluster single-molecule magnets (SMMs). The significant temperature rise results from a mechanism in the relaxation process different from that in the transition-metal-cluster SMMs. The effective energy barrier for reversal of the magnetic moment is determined by the ligand field around a lanthanide ion, which gives the lowest degenerate substate a large |Jz| value and large energy separations from the rest of the substates in the ground-state multiplets.
2,124 citations
TL;DR: In this article, the results of low-temperature experiments on a single crystal composed of superparamagnetic manganese clusters (Mn12-ac) were reported, which clearly demonstrate the existence of quantum-mechanical tunnelling of the bulk magnetization.
Abstract: THE precise manner in which quantum-mechanical behaviour at the microscopic level underlies classical behaviour at the macroscopic level remains unclear, despite seventy years of theoretical investigation. Experimentally, the crossover between these regimes can be explored by looking for signatures of quantum-mechanical behaviour—such as tunneling—in macroscopic systems1. Magnetic systems (such as small grains, spin glasses and thin films) are often investigated in this way2–12 because transitions between different magnetic states can be closely monitored. But transitions between states can be induced by thermal fluctuations, as well as by tunnelling, and definitive identification of macroscopic tunnelling events in these complex systems is therefore difficult13. Here we report the results of low-temperature experiments on a single crystal composed of super-paramagnetic manganese clusters (Mn12-ac), which clearly demonstrate the existence of quantum-mechanical tunnelling of the bulk magnetization. In an applied magnetic field, the magnetization shows hysteresis loops with a distinct 'staircase' structure: the steps occur at values of the applied field where the energies of different collective spin states of the manganese clusters coincide. At these special values of the field, relaxation from one spin state to another is enhanced above the thermally activated rate by the action of resonant quantum-mechanical tunnelling. These observations corroborate the results of similar experiments performed recently on a system of oriented crystallites made from a powdered sample4.
1,542 citations
TL;DR: In this paper, it was shown that even smaller particles can be used either by working at lower temperatures or by taking advantage of the onset of quantum size effects, which can make nanomagnets candidates for the construction of quantum computers.
Abstract: Magnets are widely used in a large number of applications, and their market is larger than that of semiconductors. Information storage is certainly one of the most important uses of magnets, and the lower limit to the size of the memory elements is provided by the superparamagnetic size, below which information cannot be permanently stored because the magnetization freely fluctuates. This occurs at room temperature for particles in the range of 10–100 nm, owing to the nature of the material. However, even smaller particles can in principle be used either by working at lower temperatures or by taking advantage of the onset of quantum size effects, which can make nanomagnets candidates for the construction of quantum computers.
1,372 citations
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01 Jan 1993
TL;DR: In this paper, the authors present an introduction to the theory and a summary of the results thereof of Quantum Tunneling of Magnetization (QTM) and discuss the role of dissipation in QTM.
Abstract: In the past couple of years, interest in Quantum Tunneling of Magnetization (QTM) has grown significantly. Since the phenomenon had tended to be regarded as a mere curiosity and mathematical game for theorists to play around with, QTM had to wait for the recent experimental work being carried out at Grenoble, Barcelona, and IBM-Yorktown in order to be of great interest to experimentalists at large. Most of the basic theoretical groundwork has been laid; we present an introduction to the theory and a summary of the results thereof. We look forward to experimentalists to refine techniques of preparing and characterizing samples, making magnetic measurements, and, with the help of theoretical analysis, improving on our ability to analyze and interpret data from magnetization measurements. We can be sure that QTM is manifested in experimental results only when we have carried out a thorough analysis of the full range of manifestations of classical processes. In this regard, we discuss the work of Bernard Barbara and this author in developing further the theory of magnetic relaxation in composites by introducing the barrier plot, which is a surface plot of the distribution of energy barriers with respect to both the energy and the applied field. Next, we discuss the domain wall junction, which has great potential in exhibiting QTM. Finally, we discuss the role of dissipation in QTM.
127 citations