Magnetic anisotropy adjusted laminated magnetic thin films for magnetic recording
View Patent ↗Multiple embodiments of the invention are described which include at least two laminated ferromagnetic layers with differing magnetic anisotropy. The independent magnetic layer farther away from the recording head is selected to have a lower magnetic anisotropy to allow magnetic switching of the multiple magnetic layers to occur at approximately the same head write current even though the recording head field is reduced with increased distance from the head. The improved switching yields improved magnetic recording performance. Laminated magnetic media according to the invention can have a single peak in the normalized DC erase noise vs. head write current plot indicating that the magnetic transitions in the non-slave magnetic layers are written at the same head write current. As a result the magnetic pulse width (PW 50 ) is reduced, overwrite (OW) is improved and media signal-to-noise ratio (S o NR) is improved. Alternatively one or both of the laminated ferromagnetic layers can be replaced with an antiferromagnetically (AF) coupled layer structure that has an AFC-master and an AFC-slave layer separated by a spacer layer selected to antiferromagnetically couple the AFC-master and AFC-slave layers.
1. A thin film magnetic recording medium for use with a magnetic recording head comprising:
a layer stack on a substrate, said layer stack comprising;
a first antiferromagnetically coupled magnetic layer structure having a; and first AFC-master ferromagnetic layer and a first AFC-slave; ferromagnetic layer that are antiferromagnetically coupled across a first spacer layer, the first AFC-master ferromagnetic layer having a first magnetic anisotropy;
a second spacer layer adjacent to the first AFC-slave ferromagnetic layer; and
a second antiferromagnetically coupled magnetic layer structure, disposed below the first antiferromagnetically coupled magnetic layer structure and the second spacer layer, having a second AFC-master ferromagnetic layer and a second AFC-slave ferromagnetic layer that are antiferromagnetically coupled across a third spacer layer, the second AFC-master ferromagnetic layer having a second magnetic anisotropy that is lower than the first magnetic anisotropy by an amount selected to compensate for a lower magnetic field from the magnetic recording head due to a larger distance between the magnetic recording head and the second AFC-master ferromagnetic layer, the second antiferromagnetically coupled magnetic layer structure being disposed so that the second spacer layer separates the second AFC-master ferromagnetic layer from the first AFC-slave ferromagnetic layer.
2. The thin film magnetic recording medium of claim 1 wherein the first AEC-master ferromagnetic layer switches in response to a first magnetic field generated by a first write current magnitude in the magnetic recording head and the second AFC-master ferromagnetic layer switches in response to a second magnetic field generated by a second write current magnitude in the magnetic recording head and the first and second write current magnitudes are approximately equal.
3. The thin film magnetic recording medium of claim 1 wherein normalized DC erase noise plotted versus a write current in the magnetic recording head has a single peak.
4. The thin film magnetic recording medium of claim 1 wherein the first and second AFC-master ferromagnetic layers include cobalt and platinum and the second AFC-master ferromagnetic layer has a lower atomic percentage of platinum than the first AFC-master ferromagnetic layer.
5. The thin film magnetic recording medium of claim 1 wherein the first and second AFC-master ferromagnetic layers comprise cobalt, platinum, chromium and boron and the second AFC-master ferromagnetic layer has a lower atomic percentage of platinum than the first AFC-master ferromagnetic layer.
6. The thin film magnetic recording medium of claim 1 wherein the first AFC-master ferromagnetic layer has a magnetization which is higher than a magnetization of the second AFC-master ferromagnetic layer.