Structure to generate low Hc in Tunnel Valve Free layer
Original Publication Date: 2002-Apr-14
Included in the Prior Art Database: 2003-Jun-21
High magnetoresistance magnetic tunnel junction structures have recently been reported in publications (e.g. W. Wulfhekel et al., Appl. Phys. Lett., 78, 509 (2001)). These structures use BCC Fe free and pinned layers along with a MgO barrier to generate high magnetoresistance. One possible structure is: PtMn/Fe/MgO/CoFe/NiFe/Ta. ABCC pinned layer structure may raise the Hc of the free layer through undesired crystal orientation. This high Hc in the free layer can induce magnetic noise. It is known that a "Cu" underlayer improves the Hc of the CoFe ferromagnetic film (US patent 5688605). I disclose the following structure to achieve low Hc in the tunnel valve free layer using ABCC crytal structure. PtMn/Fe/MgO/CoFe/CoZrNb/Cu/CoFe/Cu/Ta CoZrNb is an amorphous alloy and stops the epitaxial growth influence of layers below it. This essentially provides a fresh surface for the growth of desired crytal orientation (e.g. FCC). I further use "Cu" on top of this layer to lower the Hc in materials grown above CoZrNb/Cu layers. The CoFe layer next to MgO barrier is usually very thin 5 to 10 A). The purpose of this layer is to yield high magnetoresistance. The other ferromagnetic layers: CoZrNb and CoFe grown on top of it lead to low Hc for the entire free layer. The "Cu" layer between CoZrNb and CoFe can couple them ferromagnetically or antiferromagnetically depending on the thickness of the "Cu" layer. Therefore net magnetic thickness of the free layer can be adjusted by this method.