[14p-P10-1~98] 10 スピントロニクス・マグネティクス（ポスター）

▲ [14p-P10-56] Double hysteresis loop driven by exchange coupling in Cr₂O₃/Pt/Co positive exchange coupled thin film system

〇野崎 友大¹、Al-Mahdawi Muftah K. O.¹、Satya Prakash Pati¹、葉 術軍¹、佐橋 政司^1,2 (1.東北大院工、2.ImPACTプログラム)

キーワード：exchange bias, Cr2O3, domain

In exchange bias systems, when the antiferromagnet is multi-domain state, usually a single hysteresis loop with averaged exchange bias (H_ex) is observed. However, sometimes a double hysteresis loop with local H_ex is observed. The double hysteresis loop was explained in terms of the lateral ferromagnetic (FM) and antiferromagnetic (AFM) domain size [1]. When the FM domain size is smaller than or comparable to the AFM domain size, such a double hysteresis loop will be obtained. In Cr₂O₃/spacer/Co perpendicular exchange coupling system, a perpendicular exchange bias switching was achieved by using magnetoelectric effect of Cr₂O₃[2,3] or using positive exchange bias phenomena[4]. During such a switching, both the single and double hysteresis loop has been observed depend on the sample structure; when Pt spacer was used, single hysteresis loop was observed[2,4], while when Cr spacer was used, double hysteresis loop was observed[3]. In this study, we investigated the AFM multi-domain state of the Cr₂O₃/Pt/Co thin film system exhibiting positive exchange bias and observed both the single and double hysteresis loop, by changing Pt spacer thickness or measurements temperature. Our results indicate the single/double hysteresis loop state can be controlled by changing H_ex magnitude, even if the sample structure keep unchanged. We consider the conditions to obtain the double hysteresis loop state in terms of the energy of the system; there’s competition of energy to form domain wall in Co layer and to align Co parallel to Cr interface spin against exchange coupling. Larger H_ex make the latter energy increase, which become driving force to make domain wall in Co layer, results in the observation of the double hysteresis loop. That is, in other word, the AFM domain can be imprinted to neighbor FM domain if the H_ex magnitude is sufficiently large. Such a FM domain size control would have important role for the design of device applications.
This work was partly funded by JSPS KAKENHI Grant Number 16H05975 and ImPACT Program of Council for Science, Technology and Innovation (Cabinet Office, Japan Government).