Exchange-biased spin valves combining a high magnetoresistance ratio with soft-magnetic behavior

\u3cp\u3eWe report on the preparation of bottom spin valves combining a high giant magnetoresistance effect (above 10%) with a soft-magnetic behavior (coercivities of a few hundreds of A/m). By optimization of film composition and preparation conditions, it is possible to obtain materials having magnetoresistance values around 16%, which display minor loop coercivities of 0.2 kA/m, and sensitivities of 11%/kA/m.\u3c/p\u3

Magnetoresistance in Ni\u3csub\u3e80\u3c/sub\u3eFe\u3csub\u3e20\u3c/sub\u3e/Cu/Ni \u3csub\u3e80\u3c/sub\u3eFe\u3csub\u3e20\u3c/sub\u3e/Fe\u3csub\u3e50\u3c/sub\u3eMn\u3csub\u3e50\u3c/sub\u3e spin valves with low coercivity and ultrahigh sensitivity

\u3cp\u3eWe present magnetoresistance measurements on Ni\u3csub\u3e80\u3c/sub\u3eFe \u3csub\u3e20\u3c/sub\u3e/Cu/Ni\u3csub\u3e80\u3c/sub\u3eFe\u3csub\u3e20\u3c/sub\u3e/Fe\u3csub\u3e50\u3c/sub\u3eMn\u3csub\u3e50\u3c/sub\u3e spin valves with crossed anisotropies: the easy magnetization direction of the unbiased Ni\u3csub\u3e80\u3c/sub\u3eFe\u3csub\u3e20\u3c/sub\u3e layer is perpendicular to the exchange biasing field which effectively works on the second Ni\u3csub\u3e80\u3c/sub\u3eFe \u3csub\u3e20\u3c/sub\u3e layer due to the interaction with the Fe\u3csub\u3e50\u3c/sub\u3eMn \u3csub\u3e50\u3c/sub\u3e layer. The hysteresis in the low-field magnetoresistance is less than 0.03 kA/m, which is ten times smaller than the hysteresis for similar materials with parallel anisotropies. The sensitivity (∂R/R \u3csub\u3e∞\u3c/sub\u3e)/∂H ranges from 8% to 18%/(kA/m), depending on the preparational method. To our knowledge this combination of very high sensitivity and very low coercivity has not been reported before.\u3c/p\u3

Giant magnetoresistance and its application in recording heads

A short overview is given of the giant magnetoresistance (GMR) effect and its device applications. As an example of present research topics, the optimization of the ferromagnetic-layer composition of spin valves for application in recording heads is discussed. The influence on output voltage and stability has been investigated in test structures and compared with material parameters that were experimentally obtained from unpatterned films. It is found that in practical applications a small addition of cobalt is advantageous, since, although the output voltage is decreased, it leads to an improvement in reproducibility, linearity, signal-to-noise ratio and dynamic range

Thermally assisted reversal of exchange biasing in NiO and FeMn based systems

The stability of the exchange bias field Heb has been studied for magnetron sputtered NiO/Ni66Co18Fe16 and Ni66Co18Fe16/FeMn bilayers. A forced antiparallel alignment of the ferromagnetic magnetization to Heb results in a gradual decrease of Heb as a function of time for NiO as well as FeMn based samples. The observed decrease of Heb increases with temperature and is interpreted as a thermally assisted reversal of magnetic domains in the antiferromagnetic layer

MBE-grown spin valves

\u3cp\u3eSpin valves were grown by vapour deposition in an MBE system, instead of the usual sputter deposition. Compared to sputtered samples, the GMR ratio Δ R / R was slightly lower and the exchange-bias field was halved. Also, the (111) texture was much less pronounced. The Ta buffer layer was studied by TEM analysis, providing new information about the required structure to initiate the (111) texture.\u3c/p\u3

Performance of Yoke type GMR heads

\u3cp\u3eYoke type spin valve giant magnetoresistive (GMR) heads with a track width of 70 and 10 µm are studied. The head design has the sensor on top. The output of the heads is found to be upto 10 times larger than similar heads with a 30 nm Ni-Fe MRE linearized using a barberpole. The crucial role of the free layer permeability μ\u3csub\u3er\u3c/sub\u3e and the ferromagnetic interlayer coupling with respect to the head performance is analysed. This is argued to give design rules for the GMR material. The applied FeMn exchange biasing is shown to become unreliable above T=105°C.\u3c/p\u3

1/f noise in anisotropic and giant magnetoresistive elements

Microfabricated magnetoresistive elements based on either the anisotropic or the giant magnetoresistance effect were tested for their frequency dependent resistance noise behavior at room temperature in a dc magnetic field, using a dc sense current. Thermal resistance noise was the dominant noise source above about 10 kHz. At low frequencies the resistance noise was found to be dominated by a 1/f contribution that depends on the applied magnetic field. The 1/f noise is relatively low and field independent when the element is in a saturated state and contains a relatively large and field dependent excess contribution when the magnetic field is in the sensitive field range of the element. The 1/f noise level observed in saturation is comparable to the 1/f noise level found in nonmagnetic metals; the excess noise has a magnetic origin. The variation of the excess noise level with the applied dc magnetic field can be explained qualitatively using a simple model based on thermal excitations of the magnetization direction