Interaction of multiferroic properties and interfaces in hexagonal LuMnO₃ceramics

Abstract

A study on the underlying interaction mechanisms between lattice constants, magnetic and dielectric properties with inhomogeneities or internal interfaces in hexagonal, off-stoichiometric LuMnO 3 oxide is presented. By increasing Mn content the a-axis constant and volume of the unit cell, the antiferromagnetic (AFM) Néel temperature, T N , and frustration factor of the frustrated Mn 3+ trimmers in basal plane show decreasing trends. It was found that increasing annealing time improves properties of the lattices and progressively eliminates secondary phases for compositions within the solid solution stability limits. A magnetic contribution below T N is observed for all samples. Two regimes of magnetization below and above 45 K were observed in the AFM state. The magnetic contribution below T N is assigned to either secondary phase or internal interfaces like ferroelectric (FE) domain walls. Magneto-dielectric coupling at T N is preserved in offstoichiometric ceramics. The presence of a low temperature anomaly of the dielectric constant is correlated to composition of the solid solution in off-stoichiometric ceramics. Large FE domains are observed in PFM images of doped and un-doped ceramics, whereas atomic structure analysis indicates parallel formation of nano-sized FE domains. Combination of measured properties and microscopy images of micron-and nano-sized domains ascertain the role of lattice distortion and stability of solid solution on multiferroic properties.

Link of Weak Ferromagnetism to Emergence of Topological Vortices in Bulk Ceramics of h-LuMnxO3 Manganite

“…The composition of the LuMn x O 3 phase of both x = 1.04 and x = 1.08 samples ought to be almost identical as x = 1.04 represents the upper bound of the solid solution stability range of this phase. 4 When the annealing temperature of 1450 °C and 40 K/min cooling rate were used for testing the x = 0.94 sample of Lu excess, no vortex pattern at all was seen in PFM analysis. Annealing temperatures were increased in steps of 30 °C for sample x = 0.94 while the cooling rate was kept constant at 40 K/min.…”

“…Self-doping done both in LuMn x O 3 and in YMn x O 3 ceramics resulted in significant changes of the Curie−Weiss temperature T CW 4,17,18 but modified to a lesser extent the Neél temperature of AFM ordering. Values of T CW extracted from temperaturedependent magnetization measurements of as-sintered ceramics were of a given range from T CW = −760 °C (x = 0.92) to T CW = −528 °C (x = 1.08).…”

“…4 excess sides of LuMn x O 3 ceramics. 4 To shed further light on intercalation of broken Z 6 symmetry in FE walls in relation to multiferroic properties, the magnetic response of representative h-LuMn x O 3 samples containing different densities of FE vortices was investigated (Figure 5a−d). Zero-field-cooled temperature-dependent magnetization and field-cooled magnetization of x = 0.94, 1.00, 1.04, and 1.08 samples can be found in the Supporting Information, Figure S3a,b.…”

“…Difficulties in investigation of FE vortices arise from chemical shifts either in cation sites ,,, or in oxygen content. ,, Vacancy doping modifies unit cell and lattice parameters so that it changes the T C as much as T CW . Magnetic measurements in ceramics showed a much slenderer shift of antiferromagnetic ordering temperature, the frustration factor being dominated by changes in T CW .…”

“…Our research paid attention to the effect of vacancies in either the rare-earth site or Mn site in h-REMnO 3 ceramics. Lu or Mn vacancies in LuMn x O 3 ceramics remarkably change magnetic properties: inside the range of stability of the LuMn x O 3 solid solution in sintered ceramics, the Curie–Weiss temperature ( T CW ) increases with Mn/Lu = x ratio in comparison to reported values of T CW for the stoichiometric single crystal LuMnO 3 , the frustration factor ( f ) following the opposite trend . Otherwise, the Néel temperature ( T N ) and magneto-dielectric coupling temperature in those ceramics did not show much disparity in relation to what is already known of the stoichiometric composition.…”