Time domain magnetization dynamics study to estimate interlayer exchange coupling constant in Nd-Fe-B/Ni^sub 80^Fe^sub 20^ films

• Published in: Journal of magnetism and magnetic materials Vol. 468; p. 273
• Main Authors: Mandal, R, Ogawa, D, Tamazawa, Y, Ishioka, K, Shima, T, Kato, T, Iwata, S, Takahashi, YK, Hirosawa, S, Hono, K
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier BV 15.12.2018
• Subjects: Anisotropy; Coercivity; Coupling; Decoupling; Exchanging; Ferrous alloys; Interlayers; Kerr magnetooptical effect; Magnetic fields; Magnetic materials; Magnetic resonance; Neodymium; Nickel; Reduction; Studies; Thin films
• ISSN: 0304-8853; 1873-4766

Interlayer exchange coupling (Jex) between a hard magnetic Nd-Fe-B layer and a soft magnetic Ni80Fe20 layer is studied by means of time-resolved magneto-optical Kerr effect (TRMOKE) microscope. Whereas a single 16 nm thick Nd-Fe-B layer without Ni80Fe20 showed high coercivity of μ0Hc = 2 T and resonance frequency of fr = 161 GHz at external bias magnetic field of μ0Hb = 2 T due to the high anisotropy field, those of the bi-layer Nd-Fe-B (16 nm)/Ni80Fe20 (5 nm) are dramatically reduced to μ0Hc = 1.34 T and fr = 74.4 GHz. When the Nd-Fe-B and Ni80Fe20 are separated by a 1 nm thick non-magnetic Mo layer, by contrast, the coercivity recovered partially to μ0Hc = 1.9 T but the frequency further reduced to fr = 63.4 GHz. We derived Jex based on a simple macrospin model, whose value reduced from 3.9 ± 0.1 mJ/m2 for the bi-layer without the Mo layer to 0.1 ± 0.1 mJ/mP with the Mo layer. The reduction in Jex suggested that the interlayer exchange decoupling between the Nd-Fe-B and the Ni80Fe20 layers was responsible to the recovery of μ0Hc and the reduction of fr by the insertion of the non-magnetic layer. We successfully estimated the interlayer exchange coupling constant in the hard/soft magnetic bilayer system by TRMOKE and macrospin-modeling, which had been previously difficult because of its high anisotropy and high coercivity. This method is applicable also to the quantitative estimation of the intergranular exchange coupling.