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Magnetic Nanosystems: Making, Measuring, Modeling and Manipulation

The scientific goal of this effort is to investigate pathways that connect quantum mechanical mechanisms governing nano-scale magnetism with macroscopic magnetic properties emerging as the system size increases from nano- to macro- length scales. The focus ranges from low-dimensional (confined and restricted geometries) magnetic systems to homogeneous systems exhibiting magnetic texture, from modeling to fabrication, measurement and manipulation. The key goals are to examine effects of quantum confinement and reduced dimensionality in magnetic nano- and meso-scale structures, study quantum coherence and spin coupling to the environment, investigate charge and spin currents in topologic insulators and examine out of equilibrium dynamics of quantum magnetism in these systems. Advanced experimental probes, such as novel optical magnetic field sensor based on nitrogen–vacancy (NV) centers in diamond (NV-magnetoScope) and spin-polarized scanning tunneling spectroscopy (SP-STM) are used to map magnetic and electronic properties, while x-ray magnetic circular dichroism and ultra-fast magneto-optical spectroscopies provide information on element-resolved local moment and non-equilibrium charge and spin dynamics, respectively.

This research is supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering.

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Key Scientific Personnel:

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  • Excited state of the solid-state emitter is shifted by random amount Δ from the desired position. The optical 180° control pulses are applied periodically, with a delay τ. In the rotating frame, each pulse swaps the ground and the excited state, reversing the detuning Δ → −Δ.

    Much like being slightly off the frequency of a radio station destroys radio reception, the quality of light-emitting technologies has, until now, been severely limited by random fluctuations in the frequency of the emitted photons.  Scientists demonstrated how this photon detuning can be suppressed using a series of short, controlled pulses applied to the emitter.  The elegant solution is robust and applicable for many quantum systems, removing a major roadblock on the way to implementing large-scale quantum networks.

  • Scientists have discovered that the rare earth element dysprosium grown on graphene — a one atom thick layer of carbon — forms triangular-shaped islands, whereas other magnetic metals form hexagonal-shaped islands. Based on the hexagonal closed packed (hcp) bulk crystal structure of dysprosium, hexagonal islands would also have been expected. Researchers used scanning tunneling microscopy to identify the crystal structure of dysprosium on graphene. The results indicate that dysprosium grows as face centered cubic (fcc) crystals on graphene rather than hcp.

  • Researchers have found a trick that could make writing data to a hard disk as much as a thousand times faster. Recording information in today’s magnetic memory and magneto-optical drives uses an external magnetic field and/or a laser that heats up tiny spots, one at a time, to the point where the magnetic field can switch the magnetic ordering, to store single binary digits. The speed of the magnetic switching is limited by how long it takes the laser to heat the spot close to its Curie point and the external field to reverse the magnetic region.

  • Magnetism behaves very strangely in compounds of lanthanum, strontium, cobalt and oxygen, and researchers have just attained new insight into the decades-old question of why. Pure LaCoO3 is a non-magnetic, narrow-gap semiconductor at low temperatures, but it acquires magnetic properties as the temperature is raised – in contrast with most materials, which tend to lose magnetism at higher temperatures. With strontium doping the magnetic properties become more prominent until, at 18% Sr, the compound becomes metallic and ferromagnetic, like iron.

  • Researchers have shown that it may be possible to make lasers using single-layer sheets of carbon atoms — the novel material known as graphene. Lasers are made from materials that can absorb ordinary light and then emit photons that have matching waves to provide high intensity.To generate laser power, a material must first undergo a population inversion where an excess of electrons is excited.

  • Researchers have overcome a fundamental obstacle to realizing the full potential of quantum computing.They developed a method to protect quantum information while simultaneously performing calculations. When a quantum bit (qubit) interacts with the environment its quantum information is quickly destroyed. Until now, methods to decouple individual qubits from the environment isolated the qubits from each other so they could not exchange information. The scientists devised a scheme that seamlessly integrates decoupling from the environment into the quantum computation process.

  • A new material has been made to behave in two distinct ways, helping to break down a significant barrier for understanding the mechanisms of high temperature superconductivity. Known high temperature superconductors fall into two different classes — layered cuprates and iron arsenides. The undoped, parent compounds of the cuprates are insulating, while the parent compounds of iron arsenide superconductors are metallic.

  • The discovery that transition-metal clusters can behave like tiny “magnets,” i.e. single-molecule magnets (SMMs), opens up the opportunity for their applications in information storage, quantum computing, and molecular spintronics devices. A major objective of our synthetic project is on the design and synthesis of such molecular nanomagnets, based on inorganic polyoxometalate ligands given the rigidity (which infers predictability) and diversity (which allows rational chemical design) of their ligand environments.

Publications


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