Monica Amboage

I am interested in the study of the atomic structure modifications induced in solids by compression. I use high pressure as a means to tune the interplay between structural, electronic, and magnetic degrees of freedom of a variety of materials, with the aim to better understand their physical properties.

To generate high pressures a Diamond Anvil Cell is used, in which a small quantity of sample is contained in a metallic gasket and set in between two opposing brilliant-cut diamond anvils. The relatively small force applied to the diamonds is converted into a very high pressure on the sample due to the small size of the diamond culets. However, the small quantity of sample probed, and the need to access the sample through the diamonds, introduces great challenges to any type of measurement and implies the need for the large flux of a synchrotron radiation source.

One of my main research interests is the study of 3d transition metal perovskites. These systems are of great interest due to the rich variety of physical properties they display, such as metal-insulator transitions, spin-state transitions, or colossal magnetoresistance. Additionally, this structure is important geophysically as perovskite (MgFe)SiO₃ is the main component of the Earth’s mantle. I have studied mainly two systems: the nickel and cobalt perovskites. The rare earth (R) nickel perovskites RNiO₃ undergo a sharp insulator to metal transition as a function of temperature or pressure. The metallization process has been associated with the closing of a charge-transfer gap. Intense research efforts have been dedicated to the understanding of this electronic transition. The metallization temperature depends on the perovskite structure distortion through the Ni-O-Ni bonding angle value and consequently the Ni 3d-O 2p orbital hybridization, values which can be tuned by pressure. The cobalt perovskites RCoO₃ also exhibit metal-insulator transitions, and additionally cobalt ions Co³⁺ undergo spin-state transitions, from a non-magnetic low-spin ground state to an intermediate or high-spin state as temperature is increased. Pressure favours the low-spin configuration. We observe anomalous bulk modulus derivatives for LaCoO₃ and PrCoO₃, related to the pressure-induced intermediate-spin to low-spin transition.

Other materials I am currently studying crystallize in the spinel structure. For example spinel manganite MgMn₂O₄, in which Mn³⁺ shows Jahn-Teller effect and which has been studied at different levels of inversion, or semiconductors like spinel MnIn₂S₄, which displays nonlinear optical properties.

1. "Structural and optical high-pressure study of spinel-type MnIn2S4", F. J. Manjón, A. Segura, M. Amboage, J. Pellicer-Porres, J. F. Sánchez-Royo, J. P. Itié, A. M. Flank, P. Lagarde, A. Polian, V.V. Ursaki, and I. M. Tiginyanu, Phys. Stat. Sol. (b) 244, No. 1, 229–233 (2007)
2. "Volume expansion contribution to the magnetism of atomically disordered intermetallic alloys", J. Nogués, E. Apiñaniz, J. Sort, M. Amboage, M. d’Astuto, O. Mathon, R. Puzniak, S. Suriñach, J.S. Muñoz, M.D. Baró, F. Plazaola, F. Baudelet, Phys. Rev. B 74, 024407 (2006)
3. "High-pressure stability of the tetragonal spinel MgMn2O4: Role of inversion", Lorenzo Malavasi, Cristina Tealdi, Giorgio Flor and Monica Amboage, Phys. Rev. B 71, 174102 (2005)
4. "High pressure structural study of SmNiO3", M Amboage, M Hanfland, J A Alonso and M J Martínez-Lope, J. Phys.: Condens. Matter 17 (2005) S783-S788
5. "Pressure-induced Melting of Charge-Order in the Self-doped Mott Insulator YNiO3", J. L. García-Muñoz, M. Amboage, M. Hanfland, J. A. Alonso, M. J. Martínez-Lope and R. Mortimer, Phys. Rev. B 69, 094106 (2004).

Monica Amboage is Beamline scientist on the LOLA beam-line I20. Monica joined Diamond in October 2006 from the European Synchrotron Radiation Facility (ESRF) in Grenoble, France, where she developed her current research interest in the structural properties of matter under high pressure.