Spin–phonon interaction and Size effect on multiferroics YbMn₂O₅ nanorods
Chun-Chuen Yang1*, Wei-Jhe Shih1, Ting-Wei Hsu1, Yung-Hsiang Tung1, Kuen-Song Lin2, Yang Yuan Chen3
1Department of Physics, Chung Yuan Christian University, Chung-Li, Taiwan
2Department of Chemical Engineering and Materials Science, Yuan Ze University, Chung-Li, Taiwan
3Institute of Physics, Academia Sinica, Taipei, Taiwan
* presenting author:Chun-Chuen Yang, email:chunchuenyang@cycu.edu.tw
Six sizes of YbMn₂O₂ nanorods were fabricated by hydrothermal method with 240, 500, 700, 800, 900, and 1000 °C annealing temperatures. All samples are crystallized in orthorhombic with space group Pbam phase. TEM images and SAED patterns show sample sizes and direction of crystalline of six annealing temperatures, which are labeled in the form of radial ×axial length (r>×C>) as 26(8) nm×50(23) nm, 28(8) nm×49(20), 28(8) nm×50(19) nm, 29(8) nm×48(19) nm, 60(18) nm×98(34)nm, and 59(15) nm×96(32) nm, respectively。All the axial length of nanorods is parallel to c axis of the crystal.
Magnetic susceptibility show an antiferromagnetic (AFM) peak at 38 ~ 40K only in C> = 98 and 96 nm samples. The hysteresis curve at 2K also show the coercivity exist only at these two large samples. These observations implied a critical size of YbMn2O5 is between C> = 50 and 96 nm.
Variable temperature Raman spectrum of C> = 50, 98, and 96 nm samples show the offset apart from the their evolution trend of Raman peaks, as warming at zero applied magnetic field at T = 130 ~ 170K, T = 100 ~ 240K, and T = 80 ~ 130K, respectively. The 0.2 T applied magnetic suppressed the offset and implied the existence of spin-phonon interactions.

Keywords: spin-phonon, multiferroics, nanorod, RMn2O5, YbMn2O5