Function
Researcher, head of Magnetism and frustration group

Research Interests
Magnetism and superconductivity of strongly correlated electronic systems, with a focus in recent years in geometrically frustrated magnetic systems (see here for more details).

CV
1985 Engineer diploma from Institut National Polytechnique de Grenoble
1990 PhD in physics, Institut National Polytechnique de Grenoble
2006 Habilitation à diriger des Recherches, Université Joseph Fourier, Grenoble

Scientific Publications
The list can be found here.
Book on muon spectroscopy: Muon Spin Rotation, Relaxation, and Resonance — Applications to Condensed Matter published at Oxford University Press (2011).

Miscellaneous
Member of the scientific committees of `Bulletin INAC' and `La feuille rouge' the two newsletters about the scientific activities of Institut Nanosciences et Cryogénie from CEA-Grenoble.
Member of the organizing committee of the Higher European Resarch Course for Users of Large Experimental Systems (Hercules), a yearly school for users of neutron and synchrotron radiation in the fields of physics and chemistry of condensed matter or biomolecular structure and dynamics.

Geometrical frustration in magnetic systems
Geometrical frustration is the inabiblity for a system to find a unique ground state due of its geometry. The archetypal geometrically frustrated system is based on antiferromagnetically spins located at the vertices of a triangle.

The ground state of such systems is characterized by a large degeneracy. We have experimentally found that spin dynamics persists in these systems down to extremely low temperature regardless the absence or the presence of long-range magnetic order. Examples of the former case are found in the pyrochlore Yb₂Ti₂O7 [1] and in the garnet Yb₃Ga₅O₁₂ [2] whereas the ordered systems are Gd₂Sn₂O₇ [3], Gd₂Ti₂O₇ [4] and Tb₂Sn₂O₇ [5]. In these three ordered systems the muon spin-lattice relaxation rate (see Refs. [6], [7] or [8] for an introduction to the technique) is found to reach a finite value in the ordered phase when the temperature appoaches 0, demonstrating the presence of persisting spin dynamics.

A short survey of this research activity can be found in a recent article [9] published in the Clefs CEA magazine.

In addition we have discovered that even when magnetic reflections are detected by neutron diffraction, the compound may not be ordered as in a classical compound [5]. In fact, it is characterized by a distribution of flutuations times and the compound can be visualized as an assembly of dynamical domains [10].

Other works related to magnetic frustration on a three-dimensional lattice include the effect of chemical disorder in the environment of the magnetic moment [11] and the discovery of a new spin ice system [12].

We have recently extended our interest to planar magnetic systems. As a first example, we have studied NiGa₂S₄. We have found that the compound is again characterized by a large distribution of fluctuation times [13]. In the sibling compound FeGa₂S₄ we have evidenced an exotic magnetic phase transition which is unnoticed in usual macroscopic measurements [14].

If you are interested in preparing a PhD thesis on this subject, please consult this website (french version).

Selected publications

[1] First order transition in the spin dynamics of geometrically frustrated Yb₂Ti₂O₇
J.A. Hodges, P. Bonville, A. Forget, A. Yaouanc, P. Dalmas de Réotier, G. André, M. Rams, K. Królas, C. Ritter, P.C.M. Gubbens, C.T. Kaiser, P.J.C. King, C. Baines
Physical Review Letters 88, 077204 (2002)

[2] Absence of magnetic order in Yb₃Ga₅O₁₂: relation between phase transition and entropy in geometrically frustrated materials
P. Dalmas de Réotier, A. Yaouanc, P.C.M. Gubbens, C.T. Kaiser, C. Baines, P.J.C. King
Physical Review Letters 91, 167201 (2003)

[3] Probing magnetic excitations, fluctuations and correlation lengths by muon spin relaxation and rotation techniques
P. Dalmas de Réotier, P.C.M. Gubbens, A. Yaouanc
Journal of Physics: Condensed Matter 16, S4687 (2004)

[4] Magnetic density of states at low energy in geometrically frustrated systems
A. Yaouanc, P. Dalmas de Réotier, V. Glazkov, C. Marin, P. Bonville, J.A. Hodges, P.C.M. Gubbens, S. Sakarya, C. Baines
Physical Review Letters 95, 047203 (2005)

[5] Spin dynamics and magnetic order in magnetically frustrated Tb₂Sn₂O₇
P. Dalmas de Réotier, A. Yaouanc, L. Keller, A. Cervellino, B. Roessli, C. Baines, A. Forget, C. Vaju, P.C.M. Gubbens, A. Amato, P.J.C. King
Physical Review Letters 96, 127202 (2006)

[6] Muon Spin Rotation, Relaxation, and Resonance; Applications to Condensed Matter
A. Yaouanc and P. Dalmas de Réotier
International Series of Monographs on Physics, Oxford University Press, Oxford, (2011)

[7] Muon Spin Rotation and Relaxation in Magnetic Materials
A. Yaouanc
Lecture at the Paul Scherrer Institute 2^nd Summer School, Zuoz, Switzerland, 13 August 2002

[8] Introduction to Muon Spin Rotation and Relaxation
P. Dalmas de Réotier
Lecture at the University of Vienna, Austria, 17 November 2010

[9] Order and disorder: frustrated magnetism sets the example
P. Dalmas de Réotier, A. Yaouanc
Clefs CEA 56, 88 (2007-2008)
French version: Ordre et désorde: le magnétisme frustré montre l'exemple

[10] Ground state of the geometrically frustrated compound Tb₂Sn₂O₇
Y. Chapuis, A. Yaouanc, P. Dalmas de Réotier, S. Pouget, P. Fouquet, A. Cervellino, A. Forget
Journal of Physics: Condensed Matter 19, 446206 (2007)

[11] Magnetic frustration in the disordered pyrochlore Yb₂GaSbO_{7
J.A. Hodges, P. Dalmas de Réotier, A. Yaouanc, P.C.M. Gubbens, P.J.C. King, C. Baines
Journal of Physics: Condensed Matter 23, 164217 (2011)}

[12] CdEr₂Se₄: A new erbium spin ice system in a spinel structure
J. Lago, I. Zivkovic, B.Z. Malkin, J. Rodriguez Fernandez, P. Ghigna, P. Dalmas de Réotier, A. Yaouanc, T. Rojo
Physical Review Letters 104, 247203 (2010)

[13] Short-range magnetic ordering process for the triangular-lattice compound NiGa₂S₄: A positive muon spin rotation and relaxation study
A. Yaouanc, P. Dalmas de Réotier, Y. Chapuis, C. Marin, G. Lapertot, A. Cervellino, A. Amato
Physical Review B77, 092403 (2008)

[14] Evidence for an exotic magnetic transition in the triangular spin system FeGa₂S₄
P. Dalmas de Réotier, A. Yaouanc, D. E. MacLaughlin, Songrui Zhao, T. Higo, S. Nakatsuji, Y. Nambu, C. Marin, G. Lapertot, A. Amato, C. Baines
Physical Review B85, 140407(R) (2012)