X-Ray Magnetic Circular Dichroism Measurements in Ni up to 200 GPa: Resistant Ferromagnetism

Abstract

The structural stability of fcc Ni over a very large pressure range offers a unique opportunity to experimentally investigate how magnetism is modified by simple compression. K-edge x-ray magnetic circular dichroism (XMCD) shows that fcc Ni is ferromagnetic up to 200 GPa, contradicting recent predictions of an abrupt transition to a paramagnetic state at 160 GPa. Density functional theory calculations point out that the pressure evolution of the K-edge XMCD closely follows that of the p projected orbital moment rather than that of the total spin moment. The disappearance of magnetism in Ni is predicted to occur above 400 GPa.

Ion Beam Formation and Modification of Cobalt Nanoparticles

“…While multiple-scattering calculations for FCC Co predict the amplitude of the B feature should exceed that of the C feature [20,83], such a difference in relative amplitudes is not apparent in our XANES spectrum for FCC Co. However, the latter is consistent with XANES spectra for FCC Ni [84] and thin FCC Co films grown on (111) Cu substrates [85]. Figure 18(c) shows that the most obvious difference in the XANES spectra of our two standards is the more pronounced depression between features B and C for the FCC phase.…”

Hyperfine Splitting and Room-Temperature Ferromagnetism of Ni at Multimegabar Pressure

“…4, indeed persists up to 300 GPa. However, the magnetic moments calculated for T ¼ 0 K do not directly explain our experiments or x-ray magnetic circular dichroism measurements [13]. Such calculations do not answer the question if the moments, although finite, are still ordered.…”

“…However, in these cases, the collapse of ferromagnetism is associated with structural transitions of the crystal structure. In Ni, on the other hand, the ground state fcc structure is stable at least up to 200 GPa, as confirmed by the x-ray diffraction experiment [13], and it is predicted to be stable up to over 300 GPa [14].…”

“…The magnetic moment of Ni has previously been studied by x-ray magnetic circular dichroism [13,15,16] up to 200 GPa and indicates only a slight decrease. Extrapolation of the measured magnetic moment [16] to higher pressures implies a nonmagnetic phase above 250 GPa.…”

The Time-resolved and Extreme-conditions XAS (TEXAS) facility at the European Synchrotron Radiation Facility: the energy-dispersive X-ray absorption spectroscopy beamline ID24

“…The literature of the past few decades is full of pressure-induced electronic, magnetic and structural phase transitions: insulator-to-metal transitions, breakdown of ferromagnetism, onset of superconductivity, valence crossovers, triggering of chemical reactions, etc. (Minomura & Drickamer, 1962;Bastea et al, 2001;Citroni et al, 2002;Torchio et al, 2011;Gavriliuk et al, 2012). Reports of high magnetic field induced effects include new spin structures of anti-ferromagnetically coupled sublattices, magnetic quantum phase transitions, and various exotic phenomena such as non-Fermi liquid, unconventional superconductivity etc.…”