Extreme conditions of intense magnetic field and high pressure are powerful tools to tune the microscopic interactions and explore the magnetic phase diagrams of strongly-correlated electrons systems, as heavy-fermion magnets.

An introduction to the LNCMI-Toulouse pulsed field facility will be given, with a focus on recent technical advances, as the generation of non-destructive pulsed fields up to 99 T, the combination of pulsed fields up to 60 T and high pressures up to 4 GPa, and the possibility to perform neutron diffraction under long-duration pulsed fields up to 40 T. Then I will show recent experimental studies performed using these new setups.

In a first part [1-3], I will present an investigation of the three-dimensional pressure – magnetic field – temperature phase diagram of the heavy-fermion antiferromagnet CeRh2Si2 thanks to our new pressure cells. This phase diagram shows a temperature- and pressure-dependent decoupling of the critical and pseudo-metamagnetic fields, at the borderlines of antiferromagnetism and strongly-correlated paramagnetism. It is representative of a class of heavy-fermion Ising antiferromagnets, where long-range magnetic ordering is decoupled from a maximum in the magnetic susceptibility. Recent neutron diffraction results obtained in phase AF3 between 25.5 and 26 T (at ambient pressure) will also be shown.

In a second part [4-5], I will present a neutron diffraction study – with our new 40-T magnet – of URu2Si2. This paramagnetic system is well-known for its mysterious “hidden-order” phase, which develops below T0 = 17.5 K, and can be destabilized under pressure or high magnetic field. We have shown that a spin-density wave is stabilized under a high magnetic field from 35 to 39 T applied along c. The interplay between the hidden order, the magnetic and Fermi surface properties of URu2Si2 will be discussed.

These works have been done in collaboration with Dai Aoki, Fabienne Duc, Frédéric Bourdarot, Rikio Settai, Daniel Braithwaite, Keitaro Kuwahara, Hiroyuki Nojiri, Naveen Kumar, Shuhei Kurahashi, Julien Billette, Paul Frings, Xavier Tonon, Eddy Lelièvre-Berna, Louis-Pierre Regnaut and Jacques Flouquet.
References:
1. “Development of Bridgman-Type Pressure Cell for Pulsed High Magnetic Field”, R. Settai, W. Knafo, D. Braithwaite, S. Kurahashi, D. Aoki, and J. Flouquet, Review of High Pressure Science and Technology / Koatsuryoku No Kagaku To Gijutsu 25, 325 (2015).

2. “Pressure cell for transport measurements under high pressure and low temperature in pulsed magnetic fields“, D. Braithwaite, W. Knafo, R. Settai, D. Aoki, S. Kurahashi, and J. Flouquet, Rev. Sci. Instrum. 87, 023907 (2016).

3. “ Three-dimensional critical phase diagram of the Ising antiferromagnet CeRh2Si2 under extreme conditions of pressure and magnetic field“, W. Knafo, R. Settai, D. Braithwaite, S. Kurahashi, D. Aoki, and J. Flouquet, Phys. Rev. B 95, 014411 (2017)

4. “Field-induced spin-density wave beyond hidden order in URu2Si2“, W. Knafo, F. Duc, F. Bourdarot, K. Kuwahara, H. Nojiri, D. Aoki, J. Billette, P. Frings, X. Tonon, E. Lelièvre-Berna, J. Flouquet, and L.-P. Regnault, Nature Commun. 7, 13075 (2016).