Oxyde de magnésium

Résumé

L'oxyde de magnésium, communément appelé magnésie, a pour formule MgO et se présente sous la forme de poudre blanche très fortement basique absorbant l'eau et le dioxyde de carbone présents dans l'atmosphère. Étymologie « Magnésie » vient de Magnesia (l'actuelle Manisa), une région de l'ancienne Anatolie où l'on trouvait beaucoup de sa forme naturelle la périclase, ce minéral étant là mélangé avec de la magnétite et ce mélange était vendu sous le vocable de « pierres de magnésia » ce qui se contracta en « magnésie » d'une part et donna son nom aux magnétites d'autre part afin de les distinguer. Structure L'oxyde de magnésium est un cristal ionique. L'oxyde de magnésium a une structure comparable à celle du chlorure de sodium. Cela se traduit par

Un réseau d'anion oxygène formant une structure de type cubique à faces centrées
Un réseau de cation magnésium occupant l'ensemble des sites octaèdriques.

L'oxyde de magnésium est un matériau mod

Source officielle

https://fr.wikipedia.org/wiki/Oxyde_de_magn%C3%A9sium

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The single-atom bit represents the ultimate limit of the classical approach to high-density magnetic storage media. So far, the smallest individually addressable bistable magnetic bits have consisted of 3-12 atoms(1-3). Long magnetic relaxation times have been demonstrated for single lanthanide atoms in molecular magnets(4-12), for lanthanides diluted in bulk crystals(13), and recently for ensembles of holmium (Ho) atoms supported on magnesium oxide (MgO)(14). These experiments suggest a path towards data storage at the atomic limit, but the way in which individual magnetic centres are accessed remains unclear. Here we demonstrate the reading and writing of the magnetism of individual Ho atoms on MgO, and show that they independently retain their magnetic information over many hours. We read the Ho states using tunnel magnetoresistance(15,16) and write the states with current pulses using a scanning tunnelling microscope. The magnetic origin of the long-lived states is confirmed by single-atom electron spin resonance(17) on a nearby iron sensor atom, which also shows that Ho has a large out-of-plane moment of 10.1 +/- 0.1 Bohr magnetons on this surface. To demonstrate independent reading and writing, we built an atomic-scale structure with two Ho bits, to which we write the four possible states and which we read out both magnetoresistively and remotely by electron spin resonance. The high magnetic stability combined with electrical reading and writing shows that single-atom magnetic memory is indeed possible.

Nature Publishing Group2017

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Spin resonance provides the high-energy resolution needed to determine biological and material structures by sensing weak magnetic interactions(1). In recent years, there have been notable achievements in detecting(2) and coherently controlling(3-7) individual atomic-scale spin centres for sensitive local magnetometry(8-10). However, positioning the spin sensor and characterizing spin-spin interactions with sub-nanometre precision have remained outstanding challenges(11,12). Here, we use individual Fe atoms as an electron spin resonance (ESR) sensor in a scanning tunnelling microscope to measure the magnetic field emanating from nearby spins with atomic-scale precision. On artificially built assemblies of magnetic atoms (Fe and Co) on a magnesium oxide surface, we measure that the interaction energy between the ESR sensor and an adatom shows an inverse-cube distance dependence (r(-3.01+/-0.04)). This demonstrates that the atoms are predominantly coupled by the magnetic dipole-dipole interaction, which, according to our observations, dominates for atom separations greater than 1 nm. This dipolar sensor can determine the magnetic moments of individual adatoms with high accuracy. The achieved atomic-scale spatial resolution in remote sensing of spins may ultimately allow the structural imaging of individual magnetic molecules, nanostructures and spin-labelled biomolecules.

Nature Publishing Group2017

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Quantum spin networks having engineered geometries and interactions are eagerly pursued for quantum simulation and access to emergent quantum phenomena such as spin liquids. Spin-1/2 centers are particularly desirable, because they readily manifest coherent quantum fluctuations. Here we introduce a controllable spin-1/2 architecture consisting of titanium atoms on a magnesium oxide surface. We tailor the spin interactions by atomic-precision positioning using a scanning tunneling microscope (STM) and subsequently perform electron spin resonance on individual atoms to drive transitions into and out of quantum eigenstates of the coupled-spin system. Interactions between the atoms are mapped over a range of distances extending from highly anisotropic dipole coupling to strong exchange coupling. The local magnetic field of the magnetic STM tip serves to precisely tune the superposition states of a pair of spins. The precise control of the spin-spin interactions and ability to probe the states of the coupled-spin network by addressing individual spins will enable the exploration of quantum many-body systems based on networks of spin-1/2 atoms on surfaces.

American Physical Society2017

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