Jang Roh Rhee

Magnetization switching and tunneling magnetoresistance effects of synthetic antiferromagnet free layers consisting of amorphous NiFeSiB

MTJs with the synthetic antiferromagnetic (SAF) free layer consisting of CoFeSiB/Ru/CoFeSiB were prepared because a SAF structure can reduce the magnetostatic coupling. Magnetic switching and tunneling magnetoresistance (TMR) ratio of MTJs were investigated by experiment and by simulation. SAF structures show lower TMR ratio and coercivity (H/sub c/) than single free layer due to low net magnetic moment. The CoFeSiB SAF structure was found to have lower exchange energy.

Magnetoresistance and magnetization switching characteristics of magnetic tunnel junctions with amorphous CoFeSiB single and synthetic antiferromagnet free layers

To obtain low switching field (Hsw) we introduced amorphous ferromagnetic Co70.5Fe4.5Si15B10 single and synthetic antiferromagnet (SAF) free layers in magnetic tunnel junctions (MTJs). The switching characteristics for MTJs with structures 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 nanometer) were investigated and compared to MTJs with Co75Fe25 and Ni80Fe20 free layers. CoFeSiB showed a lower saturation magnetization of 560emu∕cm3 and a higher anisotropy constant of 2800erg∕cm3 than CoFe and NiFe, respectively. An exchange coupling energy (Jex) of −0.003erg∕cm2 was observed by inserting a 1.0nm Ru layer in between CoFeSiB layers. In the CoFeSiB single and SAF free layer MTJs, it was found that the size dependence of the Hsw originated from the lower Jex experimentally and by micromagnetic simulation based on the Landau-Lisfschitz-Gilbert equation. The CoFeSiB SAF structures showed lower Hsw than that of NiFe, CoFe, and CoFeSiB single structures. The Co...

Bias voltage dependence of magnetic tunnel junctions comprising double barriers and amorphous NiFeSiB layers

A double-barrier magnetic tunnel junction (DMTJ) comprising an amorphous ferromagnetic NiFeSiB was investigated to reduce bias voltage dependence of tunneling magnetoresistance (TMR) ratio. The typical DMTJ structures were Ta45∕Ru9.5∕IrMn10∕CoFe7∕AlOx∕free layer7∕AlOx∕CoFe7∕IrMn10∕Ru60 (in nanometers). Various free layers such as CoFe 7, NiFeSiB 7, CoFe3.5∕NiFeSiB3.5, and NiFeSiB3.5∕CoFe3.5 were prepared and compared. The NiFeSiB-used DMTJ shows a low root-mean-square surface roughness of 0.17 nm, a resistance of about 860Ω, a Vh (voltage where the TMR ratio becomes half of its nonbiased value) of 1.1 V, and a high junction breakdown voltage of 2.0 V. The DMTJ with an amorphous NiFeSiB free layer offers smooth surface roughness resulting in reduced interlayer coupling field and bias voltage dependence.

Structural and Magnetic Properties of Amorphous and Nanocrystalline CoFeSiB Thin Films

We have studied the structural, magnetic, and transport properties of CoFeSiB films with various Co compositions. Here, we focus on two amorphous Co₇₄Fe₄Si₁₄B₈ and nanocrystalline Co₇₈Fe₂Si₁₂B₈ thin films. Our results show that the amorphous film is a typical soft magnetic material, while the nanocrystalline film has a large saturation field. We conjecture that in the nanocrystalline film, the super-paramagnetism of nanocrystalline phase or antiferromagnetic exchange at the boundary between the amorphous and nanocrystalline phases causes the large saturation field.

Bias voltage dependence of magnetic of tunnel junctions comprising double barriers and CoFe/NiFeSiB/CoFe free layer

The typical double-barrier magnetic tunnel junction (DMTJ) structure examined in this paper consists of a Ta 45/Ru 9.5/IrMn 10/CoFe 7/AlO_x/free layer/AlO_x/CoFe 7/IrMn 10/Ru 60 (nm). The free layer consists of an Ni₁₆Fe₆₂Si₈B₁₄ 7 nm, Co₉₀Fe₁₀ (fcc) 7 nm, or CoFe t₁/NiFeSiB t₂/CoFe t₁ layer in which the thicknesses t₁ and t₂ are varied. The DMTJ with an NiFeSiB-free layer had a tunneling magnetoresistance (TMR) of 28%, an area-resistance product (RA) of 86 k Omega mum², a coercivity (H_c) of 11 Oe, and an interlayer coupling field (H_i) of 20 Oe. To improve the TMR ratio and RA, a DMTJ comprising an amorphous NiFeSiB layer that could partially substitute for the CoFe free layer was investigated. This hybrid DMTJ had a TMR of 30%, an RA of 68 k Omegamu m², and a H_c of 11 Oe, but an increased H_i of 37 Oe. We confirmed by atomic force microscopy and transmission electron microscopy that H_i increased as the thickness of NiFeSiB decreased. When the amorphous NiFeSiB layer was thick, it was effective in retarding the columnar growth which usually induces a wavy interface. However, if the NiFeSiB layer was thin, the roughness was increased and H_i became large because of the magnetostatic Neacuteel coupling

Structural and magnetic properties of amorphous and nanocrystalline CoFeSiB thin films

We have studied the structural, magnetic, and transport properties of CoFeSiB films with various Co compositions. Here, we focus on two amorphous Co 74 Fe 4 Si 14 B 8 and nanocrystalline Co 78 Fe 2 Si 12 B 8 thin films. Our results show that the amorphous film is a typical soft magnetic material, while the nanocrystalline film has a large saturation field. We conjecture that in the nanocrystalline film, the superparamagnetism of nanocrystalline phase or antiferromagnetic exchange at the boundary between the amorphous and nanocrystalline phases causes the large saturation field.