Magnetism

Magnetism, and in particular quantum magnetism, constitutes a central issue in condensed matter physics. Intimately related to magnetic fields, this research subject is naturally one of key activities in a laboratory devoted to generation of especially high fields. Magnetism is pertinent to very different systems: in insulators (oxides, inorganic and organometallic spin systems), new physics often results from low-dimensional or frustrated magnetic exchange; in metals (heavy-fermions, iron-based and cuprate systems) magnetism is related with superconductivity and, via nesting effects, with the Fermi surface. Both insulating and metallic quantum magnets are the place of intense quantum magnetic fluctuations.

Figure : Schematic representation of overlaps between different research subjects that involve magnetism.

Most of strongly-correlated-electron systems, as heavy-fermion, iron-based, cuprate, and organic materials are metallic and magnetic, and sometimes superconducting. Magnetic materials include magnetically ordered systems as ferromagnets, antiferromagnets, helical magnets, spin-density wave magnets, but also paramagnetic systems where magnetic fluctuations are present and indicate nearby magnetic instabilities. The magnetic phase diagrams of these systems can be adjusted by tuning pressure, chemical doping, and/or, notably, magnetic field. Intense magnetic fields enable continuous tuning of systems’ properties, leading to (quantum) phase transitions between different “exotic” low-temperature phases and to associated quantum critical behaviour. These new and exotic states include field-induced AF phases, Bose-Einstein condensates, spin glasses, hidden orders, reentrant superconductivity etc. Their phase diagrams result from competing magnetic interactions, quantum criticality, often in relation with Fermi surface reconstructions and magneto-structural effects.

At LNCMI, these phenomena are accessed by a unique panel of experimental techniques, including microscopic (NMR, neutron diffraction, XMCD) and macroscopic (magnetization, magnetoresistivity, ultrasound) probes, under steady fields up to 36 T, non-destructive pulsed fields up to 90 T, and destructive pulsed fields up to 180 T. High magnetic fields can be combined to extreme conditions of low temperatures (3He and dilution fridges) and high pressures (Bridgman-type cells).