Magnetic phase diagrams of multiferroic hexagonal RMnO₃ (R = Er, Yb, Tm, and Ho)

Abstract

Abstract:The magnetic phase diagrams of RMnO 3 (R = Er, Yb, Tm, Ho) are investigated up to 14 Tesla via magnetic and dielectric measurements. The stability range of the AFM order below the Néel temperature of the studied RMnO 3 extends to far higher magnetic fields than previously assumed. Magnetic irreversibility indicating the presence of a spontaneous magnetic moment is found near 50 K for R=Er, Yb, and Tm. At very low temperatures and low magnetic fields the phase boundary defined by the ordering of the rare earth moments is resolved. The sizable dielectric anomalies observed along all phase boundaries are evidence for strong spin-lattice coupling in the hexagonal RMnO 3 . In HoMnO 3 the strong magnetoelastic distortions are investigated in more detail via magnetostriction experiments up to 14 Tesla. The results are discussed based on existing data on magnetic symmetries and the interactions between the Mn-spins, the rare earth moments, and the lattice.

Phonons and hybrid modes in the high and low temperature far infrared dynamics of hexagonal TmMnO3

“…It is anticipated to also order magnetically at an unspecified lower temperature T N Th. « T N Mn [9,14] Here we present temperature dependent far-and mid-infrared emissivity and reflectivity of hexagonal Cooling further down to 80 K, and concurrent with the observation of no structural changes, the number of infrared active phonons remains constant.…”

“…[8] Its hexagonal crystal structure is built on corner-sharing bipyramids in which center lies the Mn 3+ ion surrounded by three in-plane oxygens. The MnO 5 polyhedra, with the two extra apical O 2-ions along the c axis, define a near triangular network in the ab plane where Mn 3+ longrange frustrated triangular antiferromagnetism, due to a ~120° spin arrangement, sets in at T N Mn~8 4 K. [9,10] In this lower temperature phase, TmMnO 3 has six formula units per unit cell. Neighboring spins are antiferromagnetic coupled via oxygen ions by superexchange interactions.…”

Магнитострикция гексагональных монокристаллов HoMnO-=SUB=-3-=/SUB=- и YMnO-=SUB=-3-=/SUB=-

“…Манганиты RMnO 3 (R = Gd-Lu, Y, Sc) являются мультиферроиками [6,7]. Эти материалы могут кристал-лизоваться в два структурных типа: ромбический или гексагональный.…”

“…Кроме того, в работе [8] было обнаружено, что гексагональный RMnO 3 с небольшим радиусом иона R становится орторомбическим, если одновременно применять высокое давление (4 GPa) и высокую температуру (1000 • C) [8]. Системы обоих ти-пов исследованы достаточно подробно [1,2,[6][7][8][9][10][11][12][13][14][15][16][17][18].…”

“…Магнитные фазовые диаграммы гексагонального RMnO 3 достаточно сложны, как было показано в [6,7,11]. В данных работах было сделано заключение, что эти системы имеют, по меньшей мере, два типа магнитного порядка, связанных с 4 f -и 3d-подсистемами.…”