Magnetic phase transitions in double hexagonal close packed neodymium metal-commensurate in two dimensions

Abstract

In elemental neodymium. a series of phase ansitions between multi-q modulated magnetic structures tnkes place below the magnetic ordering temperature TN. Based on extensive neulron diffraction studies of the temperature dependence of the length md orientation of the modulation vectors associated with these structures we suggest thal there exists a simple phenomenological relationship between the symmetry of the double hexagonal crystal lattice and the symmehy of the corresponding magnetic lattice. The model has a resemblance w the situation found for monolayer h l m on solid surfaces (orientational epitaxy) when considering the spin system as the adsorbate and the atomic structure as the subslrate. In one dimension, the modulaled magnetic structures are sequences of a commensurate to incommensurate Vansition Followed by incommensunle to incommensurate vansitions followed by an incommensurate lo commensmte transition. However, i n two dimensions. all the modulated magnetic sWcNres are equally well described 3s higher-order Commensmle to "mensurale msitions. where the magnetic unit cell is commensumte with the crystallographic unit cell, but rotated by some angle around the hexagonal axis with respect to the crystallographic unit cell. The rotation angle as well as the magnetic unit cell depend on temperature. The data suggest lhat the rotation angle is zem whenever there is B change from one type of multi-q structure to another. i.e.. in this case, the magnetic and the crystallogmphic unit cells are commensurate in both one and two dimensions. Previous and recent results for the light rare earth metals neodymium and praseodymium and alloys thereof, which lend supporl w this mterpremion. are reviewed.

Self-induced spin glass state in elemental and crystalline neodymium

“…1G with the defined Q vectors from these Q-pockets. The corresponding Q-space images are a direct visualization of the multi-Q nature acquired over the spatial area of the given images, and they provide a quantitative comparison to previous neutron diffraction studies (18)(19)(20)(21)(24)(25)(26). The spectral weight around these pockets, as well as blurring of the intensity of the Q states in largerscale images (Fig.…”

“…Despite more than 50 years of investigations, there is still no consensus on the magnetic ground state of Nd and the origin of the complexity reported in various experimental observations (18)(19)(20)(21)(22)(23)(24)(25)(26). Below the Néel temperature (T N ), neutron diffraction allowed observation of the onset of static multi-Q states with decreasing temperature.…”

“…In Fig. 3D, we present the simulated peaks of S(Q) in comparison with (i) the observed range of spectral weight from the Q-pockets Q A , Q B , and Q C in the SP-STM experiments [applied magnetic field (B z ) = 0 for both pristine zero-field cooled samples and samples after being exposed to magnetic field] and (ii) reported neutron diffraction data (21,25). By comparison, the SP-STM and neutron diffraction data agreed well with the simulated results in regions of lower Q values.…”

Epitaxial Ce and the magnetism of single-crystal Ce/Nd superlattices

“…Below 19.1 K, the moments tilt away from the a* direction to give a 2-q structure. 8 Further modulated struc-tures occur below 10 K corresponding to the onset of order on the cubic sites. The 4-q magnetic structure is adopted at low temperature as a result of the coupling between the cubic and the hexagonal sites.…”

“…Both the hexagonal and the cubic structures involve moments lying in the basal plane with the ordering being commensurate and incommensurate, respectively, for the two types of site. 9,8 In other Nd-based superlattices such as Pr/Nd ͑Ref. 10͒ and La/Nd ͑Ref.…”