Physikalisch-Technische Bundesanstalt (PTB): 2.52 Nanomagnetism

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Nanomagnetism

Working Group 2.52

- Magnetic Imaging
- Magnetization Dynamics

Magnetic Imaging

The section magnetic imaging deals with the characterization of nanoscale magnetic structures. For that purpose high resolution imaging methods are being developed. The techniques used are, in particular, scanning force microscopy (pdf), supplemented by measurements with a SQUID-susceptometer and a Kerr-magnetometer.
Our activities are focused on:

Development of a quantitative magnetic force microscopy (pdf):
The intention is to provide a technique that allows for a traceable measurement of magnetization and fields on a nanometer scale.
Providing measurement techniques for the characterization of nanostructures
Examples of our current work:
- Magnetic nanoparticles (MNPs) for medical applications (pdf)
  (BMBF-Project QuaNTAMed)
- Dipolar magnetic interactions in hard magnetic dot arrays (pdf)

Magnetization Dynamics

Information storage on magnetic media plays an important role for today's information society. The presently most common magnetic storage device is the hard disk drive. It has been showing an incredibly fast development in terms of storage density and data access times over the last decades which is not about to end in the upcoming years

[1].

Another magnetic storage device which might play a major role in the future is the magnetic random access memory (MRAM) [

3]. MRAM is a solid state memory chip like DRAM, SRAM or FLASH. In MRAM, however, the digital bit of information is not stored by means of an electric charge on a capacitor but by the orientation of the magnetic moment of a specially designed magnetic memory cell. Reading out the bit state of the cell is done by detecting the cell’s magneto resistance, e.g. the so-called tunnel magneto resistance (TMR).

		Programming of the cell is done by applying magnetic field pulses to the cell via a network of metallic current lines on the chip. Such MRAM are sometimes also referred to as “universal memories” as they combine several key features which were previously thought as being incompatible like non-volatility, low power consumption, unlimited write endurance and a high speed of operation.
Fig 1: Sketch of an MRAM memory matrix with TMR cells (green) and crossed metallization lines (yellow) for programming and read-out. To program the selected cell a current is applied through the two metallization lines (red) crossing at the cell. Only the superposed magnetic field at the crossing of the lines is sufficient to switch the cell magnetization.

An important question for the future application of MRAM devices is the maximum speed of the MRAM write operation. As this write operation is based on the magnetization reversal of a magnetic memory cell this question is directly related to a fundamental physical question: What is the physical ultra fast limit of magnetization reversal speed?

In our present research project this question is addressed. A time resolved magneto transport setup is used to detect the ferromagnetic precession in magnetic memory devices. Doing so we measure the ultra fast switching of the magnetization and test novel bit addressing schemes for ultra fast MRAM applications.

Literature:

[1] see e.g. Ed. Grochowski, HDD Roadmap, published online by Hitachi Global Storage inc. http://www1.hitachigst.com/hdd/hddpdf/tech/hdd_technology2003.pdf

[2] S. S. P. Parkin, K. P. Roche, M. G. Samant, P. M. Rice, R. B. Beyers, R. E. Scheuerlein, E. J. O'Sullivan, S. L. Brown, J. Bucchigano, D. W. Abraham, Yu Lu, M. Rooks, P. L. Trouilloud, R. A. Wanner, and W. J. Gallagher, J. Appl. Phys. 85, 5828 (1999).

[3] S. Tehrani, B. Engel, J.M. Slaughter, E. Chen, M. DeHerrera, M. Durlam, P. Naji, R. Whig, J. Janesky, and J. Calder, IEEE Trans. Magn. 36, 2752 (2000).

Contact

Head of Working Group		PD Dr. Hans Werner Schumacher Phone: +49 531 592 2500 Fax: +49 531 592 692500 E-mail: Hans Werner Schumacher


Address		Physikalisch-Technische Bundesanstalt Working group 2.52 Bundesallee 100 38116 Braunschweig Germany

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