Magnetic devices like hard drives, magnetic random1 access memories , molecular2 magnets, and quantum computers depend on the manipulation of magnetic properties. In an atom, magnetism3 arises from the spin and orbital momentum4 of its electrons. Magnetic anisotropy（各向异性） describes how an atoms magnetic properties depend on the orientation5 of the electrons orbits relative to the structure of a material. It also provides directionality and stability to magnetization. Publishing in Science, researchers led by EPFL combine various experimental and computational methods to measure for the first time the energy needed to change the magnetic anisotropy of a single Cobalt atom. Their methodology and findings can impact a range of fields from fundamental studies of single atom and single molecule6 magnetism to the design of spintronic device architectures. Magnetism is used widely in technologies from hard drives to magnetic resonance7, and even in quantum computer designs. In theory, every atom or molecule has the potential to be magnetic, since this depends on the movement of its electrons. Electrons move in two ways: Spin, which can loosely be thought as spinning around themselves, and orbit, which refers to an electrons movement around the nucleus8 of its atom. The spin and orbital motion gives rise to the magnetization, similar to an electric current circulating in a coil and producing a magnetic field. The spinning direction of the electrons therefore defines the direction of the magnetization in a material.The magnetic properties of a material have a certain preference or stubbornness towards a specific direction. This phenomenon is referred to as magnetic anisotropy, and is described as the directional dependence9 of a materials magnetism. Changing this preference requires a certain amount of energy. The total energy corresponding to a materials magnetic anisotropy is a fundamental constraint10 to the downscaling of magnetic devices like MRAMs, computer hard drives and even quantum computers, which use different electron spin states as distinct information units, or qubits.The team of Harald Brune at EPFL, working with scientists at the ETH Zurich, Paul Scherrer Institute, and IBM Almaden Research Center, have developed a method to determine the maximum possible magnetic anisotropy for a single cobalt atom. Cobalt, which is classed as a transition metal, is widely used in the fabrication of permanent magnets as well as in magnetic recording11 materials for data storage applications.The researchers used a technique called inelastic（无弹性的） electron tunneling spectroscopy to probe the quantum spin states of a single cobalt（钴） atom bound to an MgO layer. The technique uses an atom-sized scanning tip that allows the passage of electrons to the bound cobalt atom. When electrons tunneled through, they transferred energy the cobalt atom, inducing changes in its spin properties.The experiments showed the maximum magnetic anisotropy energy of a single atom and the longest spin lifetime for a single transition metal atom. This large anisotropy leads to a remarkable12 magnetic moment, which has been determined13 with synchrotron-based measurements at the X-Treme beamline at the Swiss Light Source. Though fundamental, these findings open the way for a better understanding of magnetic anisotropy and present a single-atom model system that can be conceivably used as a future qubit.Quantum computing14 uses quantum states of matter, and magnetic properties are such a quantum state, says Harald Brune. They have a life-time, and you can use the individual suface adsorbed atoms to make qubits. Our system is a model for such a state. It allows us to optimize15 the quantum properties, and it is easier than previous ones, because we know exactly where the cobalt atom is in relation to the MgO layer.
点击收听单词发音
1 random adj.随机的；任意的；n.偶然的行动 参考例句： The list is arranged in a random order.名单排列不分先后。 On random inspection the meat was found to be bad.经抽查，发现肉变质了。
相关文章推荐
