Pressure-induced spin fluctuations and spin reorientation in hexagonal manganites

Abstract

The magnetic structures of hexagonal manganites YMnO3 and LuMnO3 have been studied by powder neutron diffraction up to 6 GPa in the temperature range 10–295 K. At ambient pressure, a triangular antiferromagnetic (AFM) state of a Γ1 irreducible representation is stable below TN = 70 K in YMnO3. Upon the application of high pressure, a spin reorientation is induced and the triangular AFM structure evolves from Γ1 to Γ1+Γ2 representations. On the other hand, in LuMnO3 the triangular AFM state of a Γ2 irreducible representation with TN≈90 K remains stable over the entire pressure range investigated. The ordered magnetic moment values decrease under pressure with dM/dP = −0.35 μB GPa−1 in YMnO3 and −0.08 μB GPa−1 in LuMnO3. Simultaneously, a considerable increase in diffuse scattering intensity was found in YMnO3, while it was much less pronounced for LuMnO3. Both features indicate the enhancement of spin fluctuations due to geometrical frustration effects and an increase in the volume fraction of the spin-liquid state coexisting with the ordered AFM phase. The characteristic spin correlation length is weakly affected by pressure. The relationship between the pressure-induced behaviour of magnetic structure and the structural characteristics of the quasi-two-dimensional (2D) triangular network formed by Mn and O ions in hexagonal RMnO3 is analysed.

The Magnetic Phase Transition and Universality Class of h-YMnO3 and h-(Y0.98Eu0.02)MnO3 Under Zero and Applied Pressure

“…Based on our elastic data and using the same approach as described above, we found that an applied pressure of 1.5 GPa increased the ordering temperature with 3.9 K from T N(0 GPa) = 71.3(5) K to T N(1.5GPa) = 75.2(5) K. This is in general agreement with earlier neutron diffraction studies by Kozlenko et al [14,19]. They showed that the pressure indeed increases the Néel temperature, and based on measurements at zero pressure and applied pressures of 6.7 GPa, they estimated a linear relationship of the form T N = 75.0 + 1.2p K, where p is the pressure in GPa, which extrapolates to T N = 76.8 K at p = 1.5 GPa.…”

“…[19] shows that the spin direction of the Mn 3+ ions turn gradually 90 • between 0 and 9 GPa, going from the pure Γ 1 structure over a mixed Γ 1 + Γ 2 structure to a pure Γ 2 structure at 9 GPa. The ordered moment decreases from 3.27 µ B at zero pressure to 1.52 µ B at 5 GPa.…”

“…However, at this low doping rate, YEMO is expected to have magnetic properties very similar to YMO [17,18], and including the YEMO data in the present study serves to reconfirm these earlier findings. For YMO, it was earlier found by neutron diffraction with up to 6 GPa pressure that the applied pressure increases the ordering temperature by approximately 1 K/GPa [13,14], but reduces the average ordered moment [19].…”

Disorder-driven spin-reorientation in multiferroic h-YMn1−xFexO3

“…7,12,21 Moreover, the neutron diffraction data of The change of magnetic structure on Fe-doping is but compositional analogue of the changes observed across the spin-reorientation temperature (T sr ) in e.g., ScMnO 3 and HoMnO 3 , 7,17 and in YMnO 3 under pressure. 16 Therefore, here we maidenly witness the chemically-driven spin- fig.9-inset, right y-axis). These results are consistent with our µ ord and Φ-angle analyses.…”

“…Kozlenko et.al. 16 in their pressure-dependent neutron diffraction study on YMnO 3 showed that on application of up to 6GPa external pressure, pure YMnO 3 also undergoes spin-reorientation transition, analogous to temperature domain (T sr ) 7,17 in ScMnO 3 and HoMnO 3 . Lee et al 18 found via high-resolution neutron diffraction that all structural parameters abruptly change at T N ; evidencing strong and direct spinlattice coupling.…”