Collapse Of Antiferromagnetism Research Articles

Pressure-induced dimerization and collapse of antiferromagnetism in the Kitaev material α−Li2IrO3

We present magnetization measurements carried out on polycrystalline and single-crystalline samples of $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{Li}}_{2}{\mathrm{IrO}}_{3}$ under hydrostatic pressures up to 2 GPa and establish the temperature-pressure phase diagram of this material. The N\'eel temperature (${T}_{\mathrm{N}}$) of $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{Li}}_{2}{\mathrm{IrO}}_{3}$ is slightly enhanced upon compression with $d{T}_{\mathrm{N}}/dp$ = 1.5 K/GPa. Above 1.2 GPa, $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{Li}}_{2}{\mathrm{IrO}}_{3}$ undergoes a first-order phase transition toward a nonmagnetic dimerized phase, with no traces of the magnetic phase observed above 1.8 GPa at low temperatures. The critical pressure of the structural dimerization is strongly temperature dependent. This temperature dependence is well reproduced on the ab initio level by taking into account lower phonon entropy in the nonmagnetic phase. We further show that the initial increase in ${T}_{\mathrm{N}}$ of the magnetic phase is due to a weakening of the Kitaev interaction $K$ along with the enhancement of the Heisenberg term $J$ and off-diagonal anisotropy $\mathrm{\ensuremath{\Gamma}}$. Our study reveals a common thread in the interplay of magnetism and dimerization in pressured Kitaev materials.

Collapse of antiferromagnetism in hole doped La2CuO4 and electron doped Nd2CuO4

Loop-current magnetic moments of magnitude λ, reinforced by Cu2+ spin magnetic moments of magnitude μ, establish antiferromagnetism (AF) in pristine La2CuO4 and Nd2CuO4. Because of λ/μ ≈ 3, loop currents provide the major contribution (∼ 75%) to AF and Cu2+ spin magnets a minor contribution (∼ 25%). This disparity, combined with different mechanisms of destructing the respective moments by doping, explains both the precariousness of AF in hole doped La2−xAexCuO4 (Ae=Sr,Ba) and its robustness in electron doped Nd2−xCexCuO4.

Competition and/or coexistence of antiferromagnetism and superconductivity in CeRhIn5 and CeCoIn5

AbstractThe Ce compounds CeCoIn5 and CeRhIn5 are ideal model systems to study the competition of antiferromagnetism (AF) and superconductivity (SC). Here we discuss the pressure–temperature and magnetic field phase diagrams of both compounds. In CeRhIn5 the interesting observation is that in zero magnetic field a coexistence AF + SC phase exist inside the AF phase below the critical pressure $p_{\rm c}^{\rm *} \approx 2$ GPa. Above $p_{\rm c}^{\rm *} $ AF is suppressed in zero field but can be re‐induced by applying a magnetic field. The collapse of AF under pressure coincides with the abrupt change of the Fermi surface. In CeCoIn5 a new phase appears at low temperatures and high magnetic field (LTHF) which vanishes at the upper critical field Hc2. In both compounds the paramagnetic pair breaking effect dominates at low temperature. We discuss the evolution of the upper critical field under high pressure of both compounds and propose a simple picture of the glue of reentrant magnetism to the upper critical field in order to explain the interplay of antiferromagnetic order and SC.