Hydrothermally assisted synthesis of YMnO

Abstract

In this work single phase hexagonal YMnO 3 powders were prepared starting from Y(CH 3 COO) 3 Á xH 2 O, Mn(CH 3 COO) 2 Á 4H 2 O, KMnO 4 and KOH using methods of conventional (280 1C for 6 h) or microwave assisted hydrothermal synthesis (200 1C for 2 h) followed by calcination at 1200 1C for 2 h. According to FESEM analysis the calcined powders consisted of submicronic YMnO 3 particles, which were uniform in shape and size. Ceramic samples were obtained by sintering the as-synthesized powders at 1400 1C for 2 h. XRD analysis confirmed the presence of the single phase hexagonal YMnO 3 . SEM analysis showed a dense and homogeneous microstructure with typical inter-and intra-grain cracks. Magnetic measurements indicated ferrimagnetic properties that were explained by non-stoichiometry of the obtained compound and an excess of manganese that was confirmed by ICP analysis.

Influence of the orthorhombic phase content on the dielectric and magnetic properties of YMnO3

“…In this phase, both ferroelectric and magnetic orders are intimately related, as the former is induced by the latter, therefore giving rise to similar order temperatures. Hence, the antiferromagnetic order type E of this phase has a Néel temperature T o N of about 40 K whereas the ferroelectric transition is about 30 K 1,4,5,28 .…”

“…However, although the complex coupling between orbital, spin, charge and lattice degrees of freedom in perovskites gives rise to remarkable properties such as ferroelectricity or colossal magnetoresistance, there are few examples of multiferroic perovskites. Therefore, manganites such as RMnO 3 (R as rareearth element) have been classified as an important type of multiferroic materials 4 .…”

“…phase stabilized by means of special synthesis methods, as mechanochemical synthesis, annealing at high pressures or synthesis at high temperatures 1,[4][5][6] . It is noteworthy that the multiferroic order in both structures has different sources, as it is also the case for HoMnO 3 7,8 .…”

“…While hexagonal YMnO 3 is a multiferroic type-I in which the source of ferroelectricity is not in the magnetic order, orthorhombic YMnO 3 is type-II, where the ferroelectricity is induced by the magnetism of the system 9 . The hexagonal h-YMO (space group P6 3 cm) presents antiferromagnetic order with a Néel temperature T h N about 70 K and ferroelectric order below a Curie temperature T C ≃ 920 K 4,[10][11][12][13][14] . The significant difference between both transition temperatures also indicates the ferroelectric order does not have a magnetic origin.…”

“…It has been recently reported FM contribution for both o-YMO and h-YMO phase, although its origin is not clear. Different authors have suggested that it could be due to a non-stoichiometry of oxygen, disorder allocated at grain boundaries, or an alternative explanation could be the double-exchange interaction, which is a characteristic mechanism in perovskite oxides [4][5][6][7]23,26,52,55 . This ferromagnetic contribution observed in 1/χ curves should be also evident in the hysteresis loops.…”