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We report the magnetism of a ferromagnetic two phase mixture system by investigating the microstructural evolution and relevant property changes as a function of alloy composition in CoFeSiB film. The crystal structure evolved from an amorphous to hcp Co nanocrystal embedded two-phase mixture when Co concentration exceeded the critical amount (~75 at.%) confirmed through TEM and XRD. Very low coercivity value was observed in the amorphous samples. The soft magnetic properties are due to the fact that the magnetic moments of Co-rich phase are exchange-coupled via the amorphous matrix, as a consequence the magnetic anisotropies are averaged out in the amorphous system. Meanwhile, beyond 75 at. % of Co, an abrupt increase in coercivity was observed in the nanocrystalline samples where highly anisotropic Co nanocrystals were precipitated. The hard magnetic properties resulted from the magnetic decoupling (breaking of the nanocrystal-amorphous matrix-nanocrystal coupling chain) because the exchange forces are not able to overcome the magnetocrystaline anisotropy. We also found that antiferromagnetic exchange coupling existed at the nanocrystal-amorphous matrix interfaces. [ABSTRACT FROM AUTHOR]

The three kinds of double-barrier magnetic tunnel junction (DMTJ) with or without amorphous ferromagnetic Co70.5 Fe4.5Si15B10 (in at. %) free-layer were investigated to understand the effect of the free-layer on the bias voltage dependence of tunneling magnetoresistance (TMR) ratio. The DMTJ structure consisted of Ta 45/Ru 9.5/IrMn 10/CoFe 7/AlOx/free-layer 7/AlOx/CoFe 7/IrMn 10/Ru 60 (thickness in um). Various free layers, such as CoFe 7, CoFeSiB 7, and CoFe 1.5/CoFeSiB 4/CoFe 1.5 were prepared and compared. The roughness values of the interface between free-layer and tunnel barrier were continued by using the techniques of X-ray reflectivity and transmission electron microscopy. As a result, the amorphous free-layer made the interface roughness of DMTJ smoother, reducing the interlayer coupling field and suppressing the bias voltage dependence of TMR ratio at a given voltage. [ABSTRACT FROM AUTHOR]

A synthetic antiferromagnet (SAF) structure comprising two ferromagnetic amorphous CoFeSiB layers was employed as a free layer in magnetic tunnel junctions (MTJs) to enhance magnetotransport and magnetization switching performance. In Si-Si02 ha 45/Ru 9.5/IrMn 10/CoFe 7/AIO[subx]1.5/CoFeSiB t (t = 3.5,4.0,4.5, 5.0)/Ru 1.0/CoFeSiB 7-t/Ru 60 (nm) MTJ structures, the tunneling magnetoresistance (TMR) ratio, interlayer coupling field, and switching field all showed layer thickness dependence for 3.5 nm ⩽ t ⩽ 5 nm. When the CoFeSiB t layer (a lower ferromagnetic layer in the SAF structure) became thinner, a lower TMR ratio with a lower switching field was observed. Whereas, when the CoFeSiB t layer became thicker, a higher junction resistance with a lower interlayer coupling field was observed. This was resulted from the decrement of saturation magnetization and the smooth tunnel barrier/free-layer interface formation, respectively. [ABSTRACT FROM AUTHOR]

Magnetic tunnel junctions (MTJs), which consisted of amorphous CoFeSiB layers, were investigated. The CoFeSiB layers were used to substitute for the traditionally used CoFe and/or NiFe layers with an emphasis given on understanding the effect of the amorphous free layer on the switching characteristics of the MTJs. CoFeSiB has a lower saturation magnetization (Ms : 560 emu/cm³) and a higher anisotropy constant (Ku : 2 800 erg/cm³) than CoFe and NiFe, respectively. An exchange coupling energy (Jex) of -0.003 erg/cm² was observed by inserting a 1.0 nm Ru layer in between CoFeSiB layers. In the Si-SiO2-Ta 45/Ru 9.5/IrMn 10/CoFe 7/AlOx/CoFeSiB 7 or CoFeSiB (t)/Ru 1.0/CoFeSiB (7-t)/Ru 60 (in nanometers) MTJs structure, it was found that the size dependence of the switching field originated in the lower Jex using the experimental and simulation results. The CoFeSiB synthetic antiferromagnet structures were proved to be beneficial for the switching characteristics such as reducing the coercivity (Hc) and increasing the sensitivity in micrometer size, even in submicrometer sized elements. [ABSTRACT FROM AUTHOR]

Presents a study which fabricated a spin-valve by direct current magnetron sputtering with stacks of tantalum-nickel iron-iridium manganese-cobalt iron--copper-copper iron-nickel iron-tantalum. Experimental procedure; Results and discussion; Conclusion.