J. C. Fernandes

Experimental observation of quantum entanglement in low-dimensional spin systems

We report macroscopic magnetic measurements carried out in order to detect and characterize field-induced quantum entanglement in low-dimensional spin systems. We analyze the pyroborate

Magnetic and transport properties of low-dimensional oxi-borates

\mathrm{Mg}\mathrm{Mn}{\mathrm{B}}_{2}{\mathrm{O}}_{5}

Strongly disordered Heisenberg spin-1 chains : vanadium warwickites

and the warwickite

Low-energy excitations in the random magnetic chain system MgTiBO4

\mathrm{Mg}\mathrm{Ti}\mathrm{O}\mathrm{B}{\mathrm{O}}_{3}

Transport properties of the transverse charge-density-wave system Fe3O2BO3

, systems with spin

Titanium-III warwickites: A family of one-dimensional disordered magnetic systems.

5∕2

Structural and magnetic properties of the oxyborate Co 5 Ti ( O 2 BO 3 ) 2

and

Electronic calculations on the MgTiOBO 3 warwickite: A real-space renormalization approach

1∕2

Geometrical and Fe–Fe interaction effects on the charge distribution of the Fe3O2BO3 ludwigite

, respectively. By using the magnetic susceptibility as an entanglement witness we are able to quantify entanglement as a function of temperature and magnetic field. In addition, we experimentally distinguish a system exhibiting a random singlet-phase state from one with the Griffiths phase. This analysis opens the possibility of a more detailed characterization of low-dimensional materials.

Magnetism and charge ordering in Fe3O2BO3 ludwigite

Abstract Transition metal oxi-borates present a variety of interesting physical behavior associated with the presence of low-dimensional sub-units (ribbons or walls) in their structure. When transition metal ions with incomplete shells and spin S= 1 2 occupy randomly the octahedral sites in the ribbons we observe the formation of a random singlet phase in these one-dimensional structures. The magnetic behavior of ribbons randomly occupied by transition ions of spin S=1 is also investigated. When the sub-units are walls, we observe the formation of independent magnetic sub-systems which order separately. Homo-metallic systems with mixed valence ions present different types of charge ordering depending on the relative strength of the electron–electron or electron–phonon interaction.