for Giant Ma resistive Sensors

Ta 3 nm structures with crossed anisotropy. The ferromagnetic layers are weakly coupled. The measured GMR ratio is about 1.2% -smaller than the ratio derived from measurements on similar spin-valve structures. To explain the poor performance we studied the domains in the coupled ferromagnetic layers by Kerr microscopy. The magnetization processes are strongly influenced by the remaining weak ferromagnetic coupling and the occurrence of top laye bottom laye N14nFeioCom N14oFei nCo5o Ta 3 nm ,K,, Flg. I. Sketch of the investigated NiFeCo /CU /NiFeCo sandwich samples with crossed Of the magnetic anlsotroPy. compensated wall structures. These irregularities lead to reduced GMR ratios. Also the formation of 360°-walls can be observed. The samples were characterized by Ken magnetometry and magnetoresistance (MR) measurements. To distinguish I. INTRODUCTION between the GMR and anisotropic magnetoresistance (AMR) ECENTLY, Giant Magnetoresistance (GMR) effects R have been reported in many thin film systems. High sensitivities, interesting for sensor applications, are found in so-called spin-valves. Such systems are based on weakly coupled soft and hard magnetic layers. The hard layer can be pinned by several means, such as a coupled antiferromagnetic layer [l], its own coercivity [2], or an artificial antiferromagnet [3]. Here we discuss a system where induced crossed anisotropies are used to align the magnetization. A priori, such a system has advantages in terms of reduced complexity and improved thermal and chemical stability. We will present magnetoresistance measurements and domain observations on such samples and discuss effects to be overcome in order to make such a scheme effective. 11. EXPERIMENTAL Ni,,Fe,,Co,n(10 nm)/Cu(3.5 nm)/Ni,,Fe,,Co,,(lO nm)-sandwich structures were prepared on glass and silicon substrates with Ta seed layers. DC-magnetron sputtering at an Ar pressure of 5 mTorr in a multisource deposition apparatus at a base pressure below lo-* Torr was employed. The uniaxial magnetic anisotropy K,, was induced by an external magnetic field during deposition. The measured value of is typically about 1.5.103 J/m3. After deposition of the first ferromagnetic layer, anisotropies between the NiFeCo-layers. The ferromagnetic coupling constant derived from measurements on similar NiFeCoiCulNiFeCo /FeMn samples is 7.104 J/m2. The sample setup is shown in Fig. 1.