Micro-macro coupling

 

Motivation

Nowadays one major challenge for the tape recording industry is to increase the data transfer rate. For this purpose a multi-tracks protocol was developed by Tandberg Data & O-MaSS. One reading head serves to read simultaneously information from a set of adjacent individual tracks.

Solution

In order to establish the optimal parameters (geometry, size) of the multi-track reading head (Fig.1), the numerical modeling is used. Usually the shields and the media are the sizes of the order of micron while the sensor has dimensions comparables with the micromagnetic lengths of magnetic materials. The huge difference in size between different elements of the reading head requests a micro-macro coupling technique. Here we propose to evaluate the response of the sensor by micromagnetic calculations and the magnetic field issued from the media transitions by a macroscopic treatment. To evaluate this field, in the presence of the macroscopic shields characterized by a finite magnetic permeability µr, the BEM method was chosen. Besides, for the case of multi-track read heads, the magnetic potential may be estimated with a good approximation by considering a periodic system along the crosstrack direction. By using Fourier series expansion for the magnetic charge distribution, the initial BEM three-dimensional problem can be treated as a bi-dimensional one. Finally, the sensor response has to be modeled using a micromagnetic approach in order to consider the exchange interaction (Fig. 2). This macroscopic-microscopic coupling technique is applied to derive the response curves of a multitrack shielded AMR head for high density tape drives (Fig.3).

Aims

The project is focused on two main axis:
-  development of specific numerical tools dedicated to magnetic recording
-  exploitation of these numerical tools to design multi-track reading heads

Team

-  Ioana Firastrau
-  Liliana Buda
-  Jean-Christophe Toussaint
-  Jean-Pierre Nozičres

Main publications

I. Firastrau, L. D. Buda, J.-Ch. Toussaint, J.-P. Nozičres, Boundary Element Method and Micromagnetism coupling for magnetoresistive heads modeling to be published in J. Magn. Magn. Mat.


Fig.1
A shielded multi-tracks magnetic reading head (sensor and shields) flying above a longitudinal media.

Fig.2
Magnetic stable state of an AMR head. The head is exactly centered above the magnetic transitions and the vector plot is done in the plane yOz. The magnetic volume charges of the transitions (t=s=1µm) are plotted below along the cross-track direction (Oz).

Fig.3
The simulated read transfer curve of the AMR head for shields with different magnetic permeability.