The interplay of magnetic exchange intra-coupling and memory effect in Fe-doped NiO nanoparticles

Ashish Gandhi^1*, R. Pradeep², Yu-Chen Yeh¹, Tai-Yue Li¹, Chi-Yuan Wang¹, Y. Hayakawa², Sheng Yun Wu¹

¹Department of Physics, National Dong Hwa University, Hualien, Taiwan
²Research Institute of Electronics, Shizuoka University, Hamamatsu, Japan

* Presenter:Ashish Gandhi, email:acg.gandhi@gmail.com

Diluted magnetic semiconductors (DMSs) at the nanoscale have attracted enhanced attention in the scientific community because of having both charges and spin degree of freedom in a single substance to realize a new class of spintronic devices.1 According to recent findings, the magnetic transition metal (TM) 3d ion doped oxide-DMS have shown room temperature (RT) ferromagnetism which opens up their potential applications in the advanced spintronic, optoelectronic, magneto-optoelectronic devices.2, 3 In the present work, we have used hydrothermal method to synthesize well separated hexagonal shaped Fe-doped NiO NPs. An enhanced lattice expansion and decrease in the microstrain, crystal size, and Ni occupancy is noted with the increase of Fe-concentration. The obtained values of (HC, Mr) at 300 K from 0, 1, 5 and 10 % Fe-doped NiO samples are (403 Oe, 0.026 emu/g), (585 Oe, 0.031 emu/g), (148 Oe, 0.008 emu/g) and (96 Oe, 4.5×10-5 emu/g), suggesting transformation of weak-FM like properties to SPM with Fe-concentration. From observed structural and magnetic properties, we argue that, initially 1 % Fe-doping in NiO has led to perfect incorporation of Fe3+ ions into the NiO lattice at the octahedral site, and above 1 %, the amount of Fe-ions at the interstitial site which resulting in the formation of (4:1)-cluster should increase with the increase of doping concentration. This results in the formation of core-shell type structure of Ni1-xFexO NPs such that the effect of Fe-doping has led to decrease of the disordered surface spins and the increase of uncompensated-core spins with Fe-concertation resulting in transformation spin-glassy system to cluster-glassy. An enhanced thermal magnetic memory effect is noted from cluster-glassy system possibly because of increased intra-particle interactions. The outcome of this study is important for future development of diluted magnetic semiconductor spintronic devices and understanding of their fundamental physics.

References: 1Ohno, H., Science 1998, 281, 951. 2Radovanovic, P. V.; Gamelin, D. R., Phys. Rev. Lett. 2003, 91, 157202. 3Quynh Hoa, N. T.; Lee, Z.; Kang, S.-H.; Radmilovic, V.; Kim, E.-T., Appl. Phys. Lett. 2008, 92, 122508.

Corresponding author: sywu@mail.ndhu.edu.tw (SYW)

ACKNOWLEDGMENTS: This work is partly supported by Ministry of Science and Technology (MOST) at Taiwan via the project numbers MOST-107-2112-M-259-005-MY3 and MOST-107-2811-M-259-005.

Keywords: Fe-doped NiO , spin-glassy, cluster-glassy, Memory effect, Exchange bias