Soft X-ray Spectroscopy studies of ferrimagnetic Gd₆(Mn_1-x Co_x )₂₃

Truc Ly Nguyen^1,2*, Chueh- Cheng Yang³, Chia-Hsin Wang², Yaw-Wen Yang², H. J. Lin², Th. Mazet⁴, D. Malterre⁴, Y. C. Tseng^1,3, A. Chainani²

¹1. International College of Semiconductor Technology, National Chiao Tung University, Hsinchu 30010, Taiwan
²2. National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan
³3. Dept. of Materials Science Engineering, National Chiao Tung University, Hsinchu 30010, Taiwan
⁴4. Universitè de Lorraine, CNRS, Institut Jean Lamour, F-54000 Nancy, France

* Presenter:Truc Ly Nguyen, email:trucleenguyen@gmail.com

We study the electronic structure of the intermetallic series Gd₆(Mn_1-x Co_x )₂₃, x = 0.0 – 0.3, which shows a decrease in ferrimagnetic transition temperature from Tc = 489 K for x = 0.0, down to Tc = 118 K for x = 0.3 [1][2]. We have carried out X-ray photoemission spectroscopy (XPS), X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) studies of the series Gd₆(Mn_1-x Co_x )₂₃, x = 0.0, x = 0.2 and x = 0.3 at the Taiwan Light Source. XPS and XAS in combination with model calculations are employed to determine the valence configurations of Gd, Mn and Co in the series. The Mn 2p and Mn 3p XPS spectra show small systematic changes on Co substitution which can be reproduced by a systematic change of the hybridization strength in the model cluster calculations. The XPS valence band spectra show that the Gd 4f states occur at high binding energies, while the Mn 3d and Co 3d states are positioned at low binding energies. The Co 3d density of states shows a small increase at the Fermi level as a function of Co substitution. The Mn L-edge, Co L-edge and Gd M-edge XAS spectra for all compositions confirm that the local structure around the Mn, Co, and Gd ions do not change in the series Gd₆(Mn_1-x Co_x )₂₃. We could also obtain clear XMCD spectra of the Gd ions in the series which indicates nearly full Gd3+ spin magnetic moment of the Gd 4f7 configuration with S = 7/2 state. The Co L-edge XMCD spectra for x = 0.2 and x = 0.3 show that the net Co magnetic moment is antiferromagnetically coupled to the Gd magnetic moment. Further, the intensity of Co L-edge XMCD spectrum at x = 0.3 indicates a larger magnetic moment than at x= 0.2, suggesting the role of Co substitution in reducing the net magnetization and decreasing the ferrimagnetic Tc. We also report the XMCD spectra of Gd for x = 0.3 (Tc = 118 K) as a function of temperature at 25 K, 108 K, and 150 K. The Gd XMCD shows a systematic increase on decreasing temperature which follows a power-law dependence below Tc, indicative of a 3-D Heisenberg model for the magnetic behavior [3].

Keywords: Electronic structure, x-ray magnetic circular dichroism, ferrimagnetic order, x-ray photoemission, x-ray absorption