The polarized Raman spectra of orthorhombic RMnO3 series (R=La,Pr,Nd,Sm,Eu,Gd,Tb,Dy,Ho,Y) were studied at room temperature.The variation of phonon frequencies with R ionic radius rR as a whole confirms the commonly accepted Raman line assignments with two noticeable exceptions: (1) with decreasing rR the stretching Ag(1) and bending Ag(3) modes strongly mix for R=Sm to Tb, while for further decrease or rR (R=Dy,Ho,Y) the Ag(3) mode is observed at higher frequency than Ag(1) mode; (2) similar distortion-dependent mode mixing takes place for the rotational Ag(2) and O1(x) [Ag( 7)] modes. The mode mixing is particularly strong for the RMnO3 compounds with rR values close to the transition from A-type to incommensurate sinusoidal antiferromagnetic ordering at low temperatures. The frequency of rotational Ag(2) and Ag(4) modes scales to the angles of MnO6 [101] and [010] rotations, respectively, and could be used as a measure of their value.

International audienceOver the last two decades, the research activities on magnetocalorics have been exponentially increased, leading to the discovery of a wide category of materials including intermetallics and oxides. Even though the reported materials were found to show excellent magnetocaloric properties on a laboratory scale, only a restricted family among them could be upscaled toward industrial levels and implemented as refrigerants in magnetic cooling devices. On the other hand, in the most of the reported reviews, the magnetocaloric materials are usually discussed in terms of their adiabatic temperature and entropy changes (ΔTad and ΔS), which is not enough to get more insight about their large scale applicability. In this review, not only the fundamental properties of the recently reported magnetocaloric materials but also their thermodynamic performance in functional devices are discussed. The reviewed families particularly include Gd1-xRx alloys, LaFe13-xSix, MnFeP1-xAsx, and R1-xAxMnO3 (R=lanthanide and A=divalent alkaline earth)–based compounds. Other relevant practical aspects such as mechanical stability, synthesis, and corrosion issues are discussed. In addition, the intrinsic and extrinsic parameters that play a crucial role in the control of magnetic and magnetocaloric properties are regarded. In order to reproduce the needed magnetocaloric parameters, some practical models are proposed. Finally, the concepts of the rotating magnetocaloric effect and multilayered magnetocalorics are introduced

Magnetic and magnetocaloric properties of HoMn2O5 single crystals were investigated. HoMn2O5 undergoes a large conventional magnetocaloric effect around 10 K. The magnetocaloric effect was found to present a giant anisotropy. Consequently, a large magnetocaloric effect (−ΔSR,max= 12.43 J/kg K for 7 T) can be obtained simply by rotating the single crystal HoMn2O5 within the cb plane in constant magnetic field instead of moving it in and out of the magnetic field zone. This can open the way for the implementation of compact, simplified, and efficient rotary magnetic refrigerators.

We report and compare the structural, the magnetic, and the optical properties of ordered La 2 NiMnO 6 thin films and its disordered LaNi 0.5 Mn 0.5 O 3 counterpart. An x-ray diffraction ͑XRD͒ study reveals that the B-site Ni/Mn ordering induces additional XRD reflections as the crystal symmetry is transformed from a pseudocubic perovskite unit cell in the disordered phase to a monoclinic form with larger lattice parameters for the ordered phase. Polarized Raman-spectroscopy studies reveal that the ordered samples are characterized by additional phonon excitations that are absent in the disordered phase. The appearance of these additional phonon excitations is interpreted as the clearest signature of Brillouin-zone folding as a result of the long-range Ni/Mn ordering in La 2 NiMnO 6 . Both ordered and disordered materials display a single ferromagnetic-to-paramagnetic transition. The ordered films display also a saturation magnetization close to 4.8 B / f.u. and a transition temperature ͑FM-T c ͒ around 270 K while the disordered ones have only a 3.7 B / f.u. saturation magnetization and a FM-T c around 138 K. The differences in their magnetic behaviors are understood based on the distinct local electronic configurations of their Ni/Mn cations.