TY - JOUR
T1 - Boron composition dependence of magnetic anisotropy and tunnel magnetoresistance in MgO/CoFe(B) based stack structures
AU - Ikeda, Shoji
AU - Koizumi, Ryohei
AU - Sato, Hideo
AU - Yamanouchi, Michihiko
AU - Miura, Katsuya
AU - Mizunuma, Kotaro
AU - Gan, Huadong
AU - Matsukura, Fumihiro
AU - Ohno, Hideo
N1 - Funding Information:
This research was supported by the FIRST program of JSPS, Grant-in-Aid for Scientific Research (C)23560355, and the GCOE program at Tohoku University. The authors wish to thank R. Sasaki, I. Morita, T. Hirata, and H. Iwanuma for technical support in MTJ fabrication.
PY - 2012
Y1 - 2012
N2 - We investigated magnetic anisotropy and tunnel magnetoresistance (TMR) properties in MgO/(Co-0.25Fe-0.75-100-xB x stack structures with x=0, 15, 20, and 25 (in at.%). After annealing at 350 °C, the easy axis of magnetization switches from in-plane to perpendicular direction in 1.5-nm-thick CoFeB with the B composition near x=15. The effective magnetic anisotropy energy density (K-eff shows a maximum of 1.9× 10 5J/m 3 in the 1.5 nm-thick CoFeB film with x=20 annealed at 350 °C. K effis determined by the competition between contributions of interface anisotropy energy per effective CoFeB thickness (K i/t * , where t * is the effective CoFeB layer thickness) and demagnetization energy (-M 2 s/2μ-0. Bulk magnetic anisotropy energy (K-b is negligibly small with comparison to those two terms. To obtain MgO/ferromagnetic stack structure with a high K eff , materials and structures that reduce demagnetization energy while maintaining a high K i and a thin t * have to be explored. In MTJs with the higher B compositions, high TMR ratio is obtained at higher annealing temperature. High TMR ratio of 136% is observed in a MTJ with x=25 annealed at 350 °C.
AB - We investigated magnetic anisotropy and tunnel magnetoresistance (TMR) properties in MgO/(Co-0.25Fe-0.75-100-xB x stack structures with x=0, 15, 20, and 25 (in at.%). After annealing at 350 °C, the easy axis of magnetization switches from in-plane to perpendicular direction in 1.5-nm-thick CoFeB with the B composition near x=15. The effective magnetic anisotropy energy density (K-eff shows a maximum of 1.9× 10 5J/m 3 in the 1.5 nm-thick CoFeB film with x=20 annealed at 350 °C. K effis determined by the competition between contributions of interface anisotropy energy per effective CoFeB thickness (K i/t * , where t * is the effective CoFeB layer thickness) and demagnetization energy (-M 2 s/2μ-0. Bulk magnetic anisotropy energy (K-b is negligibly small with comparison to those two terms. To obtain MgO/ferromagnetic stack structure with a high K eff , materials and structures that reduce demagnetization energy while maintaining a high K i and a thin t * have to be explored. In MTJs with the higher B compositions, high TMR ratio is obtained at higher annealing temperature. High TMR ratio of 136% is observed in a MTJ with x=25 annealed at 350 °C.
KW - CoFeB composition
KW - MgO barrier
KW - perpendicular magnetic anisotropy
KW - tunnel magnetoresistance
UR - http://www.scopus.com/inward/record.url?scp=84867828281&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=84867828281&partnerID=8YFLogxK
U2 - 10.1109/TMAG.2012.2203588
DO - 10.1109/TMAG.2012.2203588
M3 - Article
AN - SCOPUS:84867828281
SN - 0018-9464
VL - 48
SP - 3829
EP - 3832
JO - IEEE Transactions on Magnetics
JF - IEEE Transactions on Magnetics
IS - 11
M1 - 6332756
ER -