1. Field of the Invention
This invention relates in general to magnetic transducers for reading information signals from a magnetic medium and, in particular, to an improved magnetoresistive read transducer and a method for making the improved transducer.
2. Description of the Prior Art
The prior art discloses a magnetic transducer referred to as a magnetoresistive (MR) sensor or head which has been shown to be capable of reading data from a magnetic surface at great linear densities. An MR sensor detects magnetic field signals through the resistance changes of a read element made from a magnetoresistive material as a function of the amount and direction of magnetic flux being sensed by the element.
The prior art also teaches that in order for a MR sensor to operate optimally, two bias fields should be provided. In order to bias the material so that its response to a flux field is linear, a transverse bias field is generally provided. This bias field is normal to the plane of the magnetic media and parallel to the surface of the planar MR sensor.
The other bias field which is usually employed with MR sensors is referred to in the art as the longitudinal bias field, which extends parallel to the surface of the magnetic media and parallel to the lengthwise direction of the MR sensor. The function of the longitudinal bias field is to suppress Barkhausen noise, which originates from multi-domain activities in the MR sensor.
A MR sensor for reading information signals from a magnetic recording medium is described in U.S. Pat. No. 4,103,315 to Hempstead, et al., which is assigned to the same assignee as this application. The '315 patent describes a MR read sensor which utilizes antiferromagnetic-ferromagnetic exchange coupling to produce a uniform longitudinal bias in the MR layer of the sensor. The materials suggested by the '315 patent are nickel-iron (NiFe) as the ferromagnetic MR layer and a manganese (Mn) alloy as the antiferromagnetic layer. Of the possible Mn alloys, iron-manganese (FeMn) appears to exhibit the greatest ability to exchange couple with the NiFe layer, and the FeMn is deposited directly on the NiFe to obtain the exchange bias effect. The strength of the exchange bias field developed by the materials suggested in the '315 patent was sufficient to meet prior art requirements. However, the drive to increased recording density has led to the requirement for greater levels of exchange bias field.
The use of a thermal treatment to produce a new ternary antiferromagnetic material by diffusion between contacting layers of NiFe and FeMn is described in U.S. Pat. No. 4,809,109. This method produces a higher level of exchange bias field and an increase in the ordering temperature of the antiferromagnetic material. However, this method is not compatible with prior art manufacturing processes for thin film magnetic heads.
The prior art does not disclose an MR head which produces a high level of exchange bias which can be produced by a process which is compatible with prior art manufacturing processes for thin film magnetic heads.