Data Storage Systems Center

Spin dependent heat transfer. Using a microbridge structure with GMR films and modified 3 omega method, spin dependent thermal conductivity change is observed.

It is big challenge to measure thermal conductivity in normal direction for 100nm metal films such as CoFe using the transient thermoreflectance method. The thermal resistance of the 100nm thick metal films is too small and difficult to detect the difference from the reference signals. However, using thermal barrier such as SiNx films, the thermal decay is amplified and the thermal conductivity of CoFe films was successfully measured.

It is big challenge to measure thermal conductivity in normal direction for 100nm metal films such as CoFe using the transient thermoreflectance method. The thermal resistance of the 100nm thick metal films is too small and difficult to detect the difference from the reference signals. However, using thermal barrier such as SiNx films, the thermal decay is amplified and the thermal conductivity of CoFe films was successfully measured.

Accurate simulation models are essential to the progress of the TMR head. With continual improvement and modifications, micromagnetic simulations can provide insight into the mechanics and performance of tunneling magnetoresistive read head without extensive fabrication, decreasing both the time and cost of testing new structures. Therefore, the need for models that closely match the real parameters and dimensions of read heads has greatly increased. In this work, the permanent magnet structure providing the bias field to the free layer is modeled with shapes and dimensions closer to reality, building on results from a purely block structure. Changing the shape of the permanent magnet has a significant effect on the performance of the permanent magnet. With a block structure for the permanent magnets, the free layer tilting angle varies less and remains closer to zero degrees.

The ultimate goal of this project is to study the giant magnetothermal resistance (GMTR) phenomenon in magnetoresistive films. It is well known that the spin dependence of electron scattering is responsible for the giant magnetoresistance (GMR) effect, which discovery won 2007’s Nobel Prize in physics. Since the electrons are responsible for both electrical and thermal conduction in metals, there could be a thermal counterpart to the GMR effect, i.e., GMTR phenomenon. Thermal conductivity of magnetoresistive films are measuring. Further, GMTR phenomenon in magnetoresistive films will be measured using the transient thermoreflectance technique (pump-probe method).

The effects of the saturation magnetization and the exchange coupling of the permanent magnet in a magnetoresistive read head are studied via micromagnetic modeling. The saturation magnetization is varied from 200 – 600 emu/cm3. A higher Ms provides a more stable bias field to the free layer, with less variation across 100 heads. The exchange coupling constant is varied from 0.02e-6 – 0.5e-6 erg/cm. The higher constant also produces a bias field from the permanent magnet in the desired direction and with little variation. However, the exchange cannot easily be set to a desired value. In order to produce similar effects to those produced by the changing the exchange coupling, a soft magnetic layer is added on top of the hard magnetic layer, creating a bilayer structure to produce the bias field. The thickness of this layer is varied from 0.1nm, basically nonexistent, to 5nm. A significant decrease in variation for increasing thickness is not seen in our results.