Liuniu Tong

Study on Microstructural Characterization and Ferromagnetic Resonance in Sputtered Co/V Multilayers

The structure and magnetic properties of a series of rf sputtered ［Co(1.5nm)/V(d V )］ 20 (0.5nm≤d V ≤4nm)multilayers have been studied.The multilayers structure is found by X-ray diffraction,cross-section transmission electron microscopy,and high-resolution transmission electron microscopy to be polycrystalline with small individual columnar grains and has fairly strong fcc Co(111)and bcc V(110) texture in the film growth direction.The structural characterizations also show composition-modulated structure and severely alloyed effect.Ferromagnetic resonance measurements show relatively small g factors and 4π M eff values,which also indicates that multilayers are severely alloyed.Complicated spin wave resonance spectra were observed and analyzed.The evaluated small interlayer coupling constant shows the effect of weak exchange coupling between Co layers across V spacers.

Magnetic anisotropy and ferromagnetic resonance in Co/Pb multilayers

The magnetic properties of sputtered Co/Pb multilayers have been studied by vibrating-sample magnetometer (VSM), torque magnetometer and ferromagnetic resonance spectroscopy (FMR). Magnetic measurements show that with decreasing Pb layer thickness the perpendicular anisotropy field H u increases from 5.7 to 8.3 kOe. The interfacial anisotropy is obtained to be as small as K s = 0.006 erg/cm 2 . It is demonstrated that the increase of H u with decreasing Pb layer thickness is due to the variation of texture in h.c.p. Co along the [00.2] direction with spacer thickness. The in-plane magnetic hysteresis loops show a higher saturation field and smaller remanence ratio for thin spacer films which cannot be accounted for solely by H u and indicates the existence of antiferromagnetic (AFM) coupling between Co layers through Pb spacer. The interlayer coupling is also implied by the observation of spin wave resonance (SWR) in perpendicular FMR. From the SWR spectrum the effective exchange constant is obtained as A eff = 3.4 x 10 -7 erg/cm. A resonance peak appears on the high-field side of the uniform FMR mode, which is attributed to the AFM coupling of adjacent ferromagnetic layers producing an optical mode. The Pb layer thickness (t Pb ) dependence of the separation of the resonance fields, ΔH, between the optical mode anti uniform mode in the perpendicular FMR spectrum is fitted by ΔH = 2.80 exp (-(t Pb - 1))/1.78 (kOe) with a characteristic thickness of 1.78 nm. Thus, the coupling strength (J = M s t Co ΔH/2), in proportion to ΔH, decreases exponentially with Pb layer thickness, which is consistent qualitatively with the variation of the in-plane remanence ratio with spacer thickness.

Structure and magnetic properties of Co/V multilayers

Abstract Two series of Co/V multilayers were sputtered respectively with higher(series I) and lower(series II) deposition rates. X-ray diffraction patterns show that series II has better structural quality. The saturation magnetization ( M s ) and uniaxial perpendicular anisotropy constant ( K u ) oscillate simultaneously with vanadium thickness and no interlayer coupling was observed in series I, while spin-wave resonance and weak interlayer coupling were observed in series II. We attribute the difference to different degree of intermixing and alloy formation in the multilayers.

A study of interlayer coupling of Co/Pb multilayers

Abstract Interlayer coupling of Co/Pb multilayers was studied by magnetization and Magnetoresistance (MR) measurements and ferromagnetic-resonance (FMR). The Pb layer thickness dependence of coupling strength derived from the separation between the resonance fields of the `optical mode’ and uniform mode in perpendicular FMR spectra is consistent qualitatively with the variation of the in-plane remanence ratio and MR ratio with spacer thickness.

Concurrent variation of giant magnetoresistance and saturation Kerr rotation in NiCo/Cu multilayers

The dependences of magneto-optical effect, effective optical constants, and giant magnetoresistance (GMR) on the thickness of Cu layers were investigated in NiCo/Cu multilayers prepared by rf magnetron sputtering. A peak of saturation polar Kerr rotation θK, occurred simultaneously with that of GMR ratio when the Cu thickness is around 1.0 nm, where a clear drop of the effective optical constants n and k appeared. The peak of θK is mainly caused by the reduction of the effective optical constants, which dominate over the small drop of the effective off-diagonal elements of the dielectric tensor. The concurrent variation of GMR and θK is related to antiferromagnetic interlayer coupling, which may change the electron band structure and thus the optical and magneto-optical transitions of electrons.

Magnetooptical, optical and GMR effect in Ni–Co/Cu multilayers

Abstract A series of RF sputtered NiCo/Cu multilayers was prepared and the correlation of the interlayer coupling and magnetooptical Kerr effect (MOKE) was studied. A concurrent oscillation of the magnetoresistance ratio and the maximum Kerr rotation ( θ 2 k + η 2 k ) 1/2 with Cu layer thickness was observed. The oscillation of the Kerr rotation is attributed to changes in the band structure related to the antiferromagnetic interlayer coupling, leading to changes in the optical and magnetooptical transitions.

The magnetic properties of Co/Pb multilayers

The magnetic properties of sputtered Co/Pb multilayers have been studied. When d pb < 23 A, a perpendicular magnetic anisotropy (PMA) is found to increase with decreasing Pb thickness. The PMA is attributed mainly to the magnetocrystalline anisotropy. The observation of spin-wave resonance, and low in-plane remanence ratio suggests the existence of interlayer coupling in this system.

OSCILLATIONS OF INTERLAYER COUPLING AND MAGNETO-OPTICAL KERR EFFECT IN NICO/CU MULTILAYERS

A series of rf sputtered [NiCo(1.3 nm)/Cu(tCu)]25 multilayers with tCu=0.5–4.0 nm was prepared and the behavior of interlayer coupling, magnetoresistance, and magneto-optical Kerr effect was studied. A concurrent oscillation in the magnitude of the magnetoresistance and magneto-optical Kerr effect in visible wavelength range as a function of Cu layer thickness was observed. The changes of both the optical and magneto-optical transition due to interlayer coupling may be responsible for the magneto-optical activities.