Proof of the elusive high-temperature incommensurate phase in CuO by spherical neutron polarimetry

Abstract

CuO is the only known binary multiferroic compound, and due to its high transition temperature into the multiferroic state, it has been extensively studied. In comparison to other prototype multiferroics, the nature and even the existence of the high-temperature incommensurate paraelectric phase (AF3) were strongly debated—both experimentally and theoretically—since it is stable for only a few tenths of a kelvin just below the Néel temperature. Until now, there is no proof by neutron diffraction techniques owing to its very small ordered Cu magnetic moment. Here, we demonstrate the potential of spherical neutron polarimetry, first, in detecting magnetic structure changes, which are not or weakly manifest in the peak intensity and, second, in deducing the spin arrangement of the so far hypothetic AF3 phase. Our findings suggest two coexisting spin density waves emerging from an accidental degeneracy of the respective states implying a delicate energy balance in the spin Hamiltonian.

Future applications of the high-flux thermal neutron spectroscopy: the ever-green case of collective excitations in liquid metals

“…While the traditional area where neutron polarisation option offers unparalleled capability is the analysis of magnetic materials structure and dynamics [100][101][102][103], the application of this technique to the study of disordered non-magnetic systems remains largely unexploited. Indeed, if magnetic order is present, e.g.…”

Magnetic domains in two distinct antiferromagnetic phases of CuO

“…This monoclinic structure is characterized by zigzag Cu-O chains along the [ 10 1] direction with the Cu-O-Cu bond angle of 146°. Partly related to such a structure involving moderate magnetic frustration, this compound exhibits successive antiferromagnetic (AFM) phase transitions at T N1 = 213 K and T N2 = 230 K [3][4][5][6]. At temperature (T ) below T N1 , CuO shows a collinear AFM order, where the Cu moments point along the b axis with the commensurate (CM) propagation vector q CM (0.5, 0, −0.5), as depicted in the right panel of Fig.…”

Room-Temperature Type-II Multiferroic Phase Induced by Pressure in Cupric Oxide

“…1(d)) Several studies have demonstrated the existence of an additional phase (AF3) in an extremely narrow temperature range in the vicinity of the Néel temperature (T ∼ 230 K), [30][31][32], which is a nonpolar/nonferroelectric ICM phase. [33] As the dielectric permittivity reflects the fluctuation of the electric dipole moments around the ferroelectric phase transition, the observed dielectic anomaly is considered to correspond to the ferroelectric phase transition at T N2 . To extend the study to higher pressures, neu- GPa, the T N1 drops below the lowest attainable temperature of the experimental setup.…”