Magnetism in Ce 2Fe 17 at pressures up to 70 kbar

Abstract

The magnetic phase diagram of Ce 2Fe 17 at ambient pressure shows a ferromagnetic (FM) phase transforming into an incommensurate helical antiferromagnetic (AFM) one above Θ T=97 K, and becoming paramagnetic above T N=214 K. The FM ground state is highly unstable, d Θ T/d P=−24 K/kbar, whereas T N only moderately decreases with pressure P, d T N/d P=−1.7 K/kbar. Hence, pressures of the order of 100 kbar are necessary to suppress the magnetic ordered state in Ce 2Fe 17. The suppression of the FM phase under pressure is accompanied by the appearance of a new incommensurate antiferromagnetic (AFM1) phase at low temperatures. To investigate the stability of the magnetic state and the behaviour of the new pressure-induced AFM1 phase, powder neutron diffraction measurements were performed with P ⩽ 70 kbar. This completed the magnetic phase diagram of Ce 2Fe 17 in that region. The results clearly show that the pressure dependence of the Néel temperature is linear up to 25 kbar. The strong decrease in the intensity of the magnetic (0 0 0) + satellite with P gives clear evidence for the volume dependence of the Fe magnetic moments. Simultaneously, the incommensurate propagation vector τ =(0, 0, τ z) increases with pressure, reaching 0.72 r.l.u. at 4 K and 70 kbar. The results show the anisotropic behaviour of the exchange interactions between Fe moments in Ce 2Fe 17 and their complex dependence on volume changes.