Epitaxial Permalloy with Unique Magnetic Properties
The need for improvements in sensitivity, performance and reduction in size of magnetoresistive devices, such as non-volatile magnetoresistive random access memory (MRAM) and magnetic sensors, is the driving force behind the search for new magnetic materials. The switching characteristics, homogeneity of magnetic domains, magnetic anisotropy and magnetic domain reversal speed (switching speed) are all critical to the performance of such devices. In recent years, non-epitaxial permalloy (Py) has become one of the favored ferromagnetic materials used in magnetic storage and sensing applications. The magnetic and transport properties of non-expitaxial Py thin films have been extensively studied. Compared to other feromagnets such as Co and Fe, non-epitaxial Py has a number of advantages, among them its softness (low coercivity). However, non-epitaxial Py thin films have single-magnetic-domain states that extend for only very short in-plane distances, limited reliability when exposed to high temperatures and slower than desired switching speeds.
Description of Technology
Epitaxial Ferromagnetic Ni3FeN (PyN) is a new material with unique magnetic properties. Nitrogen is incorporated into the nickel-iron composition to yield an intermetallic nitride. Grown epitaxially on a substrate, PyN exhibits a single magnetic domain, even for an area as large as 12 x 12 mm. The domain rotates suddenly and coherently in response to the desired switching field with a very sharp transition, so that the magnetic hysteresis loop of this new magnetic nitride is close to an ideal square. The switching field is tunable, making this soft magnetic material suitable for magnetoresistive devices.
- Low coercivity: Material is magnetically soft and thus easy to magnetize and demagnetize.
- Large domain: Single magnetic domain over large areas (as much as 12 x 12 mm).
- Fast switching speed: Domain suddenly and coherently rotates in response to an imposed switching field, and the switching field is adjustable.
- Better reliability: PyN maintains its magnetic properties after extensive thermal cycling to 500°C.
- Higher Anisotropic Magnetoresistance (AMR): Compared to standard Py, PyN has a higher AMR for greater sensitivity in sensor applications.
Could be used in variety of applications requiring soft magnetic materials such as hard disk read/write heads, magnetic storage elements, and magnetic sensors for medical applications (e.g., pacemakers).
US 7354505 (issued 8 Apr, 2008)
For Information, Contact:
Michigan State University