Hysteresis effects in the phase diagram of multiferroicGdMnO3

Abstract

We present high-resolution thermal expansion α(T ) and magnetostriction ∆L(H)/L measurements of GdMnO3, which develops an incommensurate antiferromagnetic order (ICAFM) below TN ≃ 42 K and transforms into a canted A-type antiferromagnet (cAFM) below Tc ≃ 20 K. In addition, a ferroelectric polarization P||a is observed below TFE for finite magnetic fields applied along the b direction. In zero magnetic field we find a strongly anisotropic thermal expansion with certain, rather broad anomalous features. In finite magnetic fields, however, very strong anomalies arise at Tc for fields applied along each of the orthorhombic axes and at TFE for fields along the b axis. Both phase transitions are of first-order type and strongly hysteretic. We observe a down-bending of the ICAFM-to-cAFM phase boundary Tc(H) for low magnetic fields and our data give evidence for coexisting phases in the low-field low-temperature range.The recent discovery of very large magnetoelectric effects in the rare-earth manganites RMnO 3 has reopened the field of the so-called multiferroic materials. 1,2 Multiferroic means, that several ferro-type orders like ferromagnetism, ferroelectricity or ferroelastivity coexist. The rare-earth manganites RMnO 3 may be grouped into the hexagonal ones (R= Ho,. . . , Lu) and those with orthorhombically distorted perovskite structures (R= La,. . . , Dy). The hexagonal RMnO 3 show both, ferroelectric and magnetic order, but the respective ordering temperatures differ by an order of magnitude, T FE ≃ 1000 K and T N ≃ 100 K. 3 In contrast, RMnO 3 with R = Gd, Tb, and Dy possess comparable transition temperatures for the magnetic and the ferroelectric ordering. 1,2 Both, TbMnO 3 and DyMnO 3 develop an incommensurate antiferromagnetic order (ICAFM) below about 40 K. The incommensurability continuously changes upon cooling and becomes almost constant below T c ≃ 28 K and ≃ 19 K for R = Tb and Dy, respectively. The transition to this long-wavelength incommensurate antiferromagnetic (LT-ICAFM) phase is accompanied by ferroelectric (FE) ordering with a polarization P||c, which flops to P||a above a critical magnetic field applied along the a or b direction, while it is suppressed for large fields along c. 4 GdMnO 3 also shows an ICAFM order below T N ≃ 42 K and a second transition at T c ≃ 23 K. Based on the observed weak ferromagnetism 5,6 and on X-ray diffraction studies 7 a canted A-type antiferromagnetic ordering (cAFM) has been proposed for T < T c , but a direct magnetic structure determination has not yet been published. Both transition temperatures weakly increase in a magnetic field. 4 Concerning the FE polarization, contradictory results have been reported. Kuwahara et al. 8 find a finite polarization below 13 K, while Kimura et al. 4 observe FE order only between 5 K and 8 K. The magnitude of P is much smaller than in TbMnO 3 and DyMnO 3 and the direction is P||a. Moreover, there are no magneticfield-induced polarization flops. Instead the polarization is stabilized by a magnetic field along b, while it is i...

Structural and insulator-to-metal phase transition at 50 GPa in GdMnO3

“…[16][17][18] Its phase diagram has been extensively studied as a function of external parameters: Temperature, doping, and high magnetic fields. 16,18,19 Pressure has only been explored up to 1 GPa through a pressure-dependent study of the dielectric constant at low temperatures. 20 Here, we report a pressure-dependent investigation of the lattice dynamics and crystal structure of GdMnO 3 at room temperature up to 53.2 GPa, through Raman spectroscopy and x-ray powder diffraction.…”

Structural anomalies at the magnetic and ferroelectric transitions inRMn2O5(R=Cruz1, Yen2, Lorenz3 et al. 2006Phys. Rev. B

“…9 Strong lattice anomalies have also been observed in GdMnO 3 at the transition into the FE phase that happens in this multiferroic compound at higher magnetic fields. 16 The superexchange interactions between neighboring Mn 3+ and Mn 4+ ions in the a-b plane are all AFM and the smallest closed loop of neighboring Mn spins involves five ions. Therefore, magnetic frustration must exist as, for example, revealed by the spin order in HoMn 2 O 5 displayed in the inset of Fig.…”

Coupling Between Spins and Phonons Towards Ferroelectricity in Magnetoelectric Systems

“…Published online 23 Ferroelectric materials have been and still are widely used in many applications, that have moved from sonar towards breakthrough technologies such as memories or optical devices. This book is a part of a four volume collection (covering material aspects, physical effects, characterization and modeling, and applications) and focuses on the underlying mechanisms of ferroelectric materials, including general ferroelectric effect, piezoelectricity, optical properties, and multiferroic and magnetoelectric devices.…”

“…We should highlight the importance of this result as it definitely confirms assumptions forwarded in previously published works carried out in orthorhombically distorted rareearth maganites. [17][18][19][20][21][22][23][24][25][26] What makes them a very interesting set of materials is the fact that they share a common GdFeO 3 -distortion, where the tilt angle of the MnO 6 octahedra becomes larger when the rare-earth radius decreases. This behaviour is illustrated in Figure 6 for several undoped rare-earth manganites and the Eu 1-x Y x MnO 3 doped system.…”