IEEE TRANSACTIONS ON MAGNETICS, VOL. 34, NO. 4, JULY 1998 2343 Spin Valve Heads with a Corrosion Resistant MnRh Exchange Layer Anabela Veloso, Student Member, IEEE, Paulo P. Freitas, Member, IEEE, Nuno J. Oliveira, Student Member, IEEE, Jo˜ ao Fernandes, and M´ ario Ferreira Abstract—A new exchange material, Mn Rh , is described, requiring no post-deposition anneal to obtain the antiferromag- netic phase and leading to spin valve sensors with good corrosion resistance, thermal stability up to 225 C, and good exchange coupling characteristics. Potentiodynamic polarization scans per- formed in a sodium sulfate electrolyte show that Mn Rh films exhibit a good corrosion resistance, comparable to that of Ni Fe , Mn Ir , and Mn Ni films but with higher corrosion potential. Spin valve structures prepared with this exchange material show an exchange coupling strength ( ) of 0.19 erg/cm . The blocking temperature ( ) of the as-deposited spin valve coupon samples is 235 C. Unshielded sensors with trackwidths – m and height – m were fabricated. The sensors show well-linearized magnetoresistance (MR) transfer curves, without hysteresis or Barkhausen noise and are thermally stable under consecutive 5 h anneals in vacuum up to 225 C. A shielded tape head device was fabricated showing a maximum output of 1.8 m / m, with potential for operating at linear densities near 100 kfci, at which a 580 / m output is measured. Index Terms—Corrosion resistance, exchange layers, magnetic recording/reading heads, magnetoresistive materials and devices, spin valve heads. I. INTRODUCTION S PIN valve heads require a corrosion resistant, thermally stable exchange film to keep the pinned ferromagnetic layer in a transverse orientation. Several exchange layers have been studied, including FeMn [1], TbCo [2], NiO [3], MnNi [4], Mn Ir [5], and Mn–Pt [6]. Corrosion resistance is normally compared with that of Ni Fe . From the previ- ously quoted literature, only MnNi based exchange layers [4] or NiO [7] exchange layers were shown to have better or comparable corrosion resistance with respect to that of NiFe. Corrosion resistance is important to maintain the ex- change during processing as well as during head performance. Thermal stability is controlled by the blocking temperature ( ) of the exchange bilayer. For safe head processing, should exceed the maximum temperature required during head Manuscript received January 30, 1998; revised March 26, 1998. This work was supported in part by a PRAXIS Project PRAXIS/3/3.1/TIT/11/94, and two of the authors, A. Veloso and N. J. Oliveira, were supported by PRAXIS Grants PRAXIS XXI/BD/9420/96 and PRAXIS/4/4.1/BD/1469, respectively. A. Veloso, P. P. Freitas, and N. J. Oliveira are with the Instituto de Engenharia de Sistemas e Computadores (INESC), 1000 Lisbon, Portugal, and the Physics Department, Instituto Superior T´ ecnico, 1000 Lisbon, Portugal (e- mail: anabela@pseudo.inesc.pt; ppf@eniac.inesc.pt). J. Fernandes and M. Ferreira are with the Chemical Engineering Depart- ment, Instituto Superior T´ ecnico, 1000 Lisbon, Portugal. Publisher Item Identifier S 0018-9464(98)04864-X. processing ( 240 C, for resist bake in write head fabrication [8]). For reliable head performance, the blocking temperature should exceed any thermal excursions occurring during the life of the head (thermal asperities). As the dimensions of the head shrink, the demagnetizing fields in the free and pinned layers increase. To keep the pinned layer from rotating under the demagnetizing fields, higher unidirectional exchange fields ( ) are needed. MnNi and Mn–Ni–Cr layers have the best thermal stability ( C) [4], show strong exchange (exchange constant erg/cm ) [4], and have a corrosion resistance only surpassed by NiO. However, in MnNi, the antiferromagnetic phase with a CuAu–I type ordered face-centered-tetragonal (fct) structure responsible for exchange requires several hours of post-deposition anneal at temperatures ranging from 260–300 C to be stabilized. NiO films provide very high corrosion resistance but lead to a high pinned layer coercivity ( ) comparable to and a relatively low exchange constant ( erg/cm ) [9]. In this paper, a new Mn–Rh exchange layer is described, which has a good corrosion resistance, shows good exchange coupling, does not require anneal for stabilization, and has a blocking temperature of 235 C. II. EXPERIMENTAL METHOD Spin valves with structure Si/Ta (50 ˚ A)/Ni Fe (60 ˚ A)/Co Fe (5 ˚ A)/Cu (23 ˚ A)/Co Fe (22 ˚ A)/Mn Rh (170 ˚ A)/Ta (50 ˚ A) were prepared in a load-locked magnetron sputtering system (Nordiko 2000) with a base pressure of 5 10 Torr, onto Si 100 substrates. A permanent magnet array in the deposition chamber created a 20 Oe field during the deposition, ensuring an easy axis in the pinned and free layers. For NiFe deposition a Ni–Fe19 wt% target was used. The CoFe layers were RF sputtered from a composite Co–Fe target leading to a film composition of Co Fe measured by proton induced X-ray emission (PIXE). Additional Mn Ir and Mn Ni films were prepared for posterior comparison of corrosion properties. The Mn Ni films were deposited from a composite Mn–Ni target. The starting MnRh and MnIr targets (20 at% Rh, 20 at% Ir) were obtained from MITSUI-Japan. Rutherford backscattering (RBS) analysis of Mn Rh films deposited at 3.0 mTorr indicates that at%. The corrosion resistance of the new exchange material was studied by potentiodynamic polarization experiments carried out at a scan rate of 500 V/s in a 0.1 N sodium sulfate electrolyte (concentration of 7.1 g/l ; pH = 7), and 0018–9464/98$10.00  1998 IEEE Authorized licensed use limited to: IEEE Xplore. Downloaded on April 15, 2009 at 15:19 from IEEE Xplore. Restrictions apply.