MAGNETIC ANISOTROPY AND STRUCTURE OF EPITAXIAL PERMALLOY FILMS SPUTTERED DEPOSITED ON Nb (110)

1. MAGNETIC ANISOTROPY AND STRUCTURE OF EPITAXIAL PERMALLOY FILMS SPUTTERED DEPOSITED ON Nb(110) PRESENTED BY WAFA KHALID (ID # O8)

2. The terms involved are Permalloys It is an iron nickle alloy having • High magnetic permeability • Low coercivity • Significant anisotropic magnetoresistance • Fcc structure with lattice constant of 0.355nm in the vicinity of 80% Ni.

3. Magnetic anisotropy • In absence of magnetic field material will align its moment along an easy axis. Epitaxial • growing layers on the crystal surface so that layer has same structure as of crystal. NeobiumNb • It is a soft grey ductile material of at.no 41 and M.P of 2469C.

4. Epitaxial permalloythin films sputtered deposited onto epitaxial Nb with and without copper buffer layer. • Transmission electron microscopy is used to study the morphology of Nb/Py/Cu and Nb/Cu/Pymultilayers. • Rotational magnetization measurements indicate differences in the magnetic anisotropy of the films. • The correlations between crystal structures and the magnetic properties have been discussed.

5. The Py layers in polycrystalline samples are usually magnetically isotropic, and grow with columnar grain structures. • Py(111) fcc is magnetically isotropic so grow epitaxially on Cu (111) fcc because they have same crystal structures.

6. AIM OF THE PAPER • We study the structural and magnetic studies of epitaxial Nb/Cu/Py and Nb/Py/Cu multi layers. • Study the effects of the buffer layers on the Py layer morphology are compared using cross-sectional transmission electron microscopy TEM!. • We study the rotational magnetization measurements to determine the strength of the magnetic anisotropy. • We correlate the magnetic properties with the structures of the epitaxial Py films and the buffer layers, and show that the magnetic properties of Py grown epitaxially on Nb are likely determined by the uniaxial strain-induced magnetic anisotropy, due to the lattice mismatch of Nb and Py.

7. Py films are triode sputtered on epitaxial bilayers of Alumina/Nb/Cu or onto epitaxial films of Aumina/Nb. • Deposition of films occurs in a chamber of base pressure 2×10*8 Torr. We have selected two samples for comparing our results. • Nb(200nm)/Cu(20nm)/Py(20nm)/Nb(20nm) • Nb(200nm)/Py(20nm)/Cu(20nm)/Nb(20nm) The growth temprature of Nb (200nm) is 750C a

8. The crystallographic orientations of sputtered epitaxial Nb, Cu and Py.

10. At room temprature, the coercive field was 10 Oe when permalloy is deposited on Cu buffer layer. • The corecive field was 30 Oe for permalloy deposited directly on Nb layer. The differences in the coercivity is due to the difference in strain induced anisotropy.

11. When Cu and Py are grown epitaxially on substrate, there is lower magnetic anisotropy because lattice mismatch between them is isotropic is 2%. • Nb is bcc(110) while Py and Cu are fcc so there comes a lattice mismatch of 28% and are magnetically anisotropic.

12. The difference between the strength of uniaxial anisotropy in samples A and B can be explained by the uniaxial strain relaxation in the 20-nm-thick Cu buffer layer in sample A, compared to the sample B, where Py was grown directly on Nb. • The slight breakdown of the epitaxy of sample B, shown from the diffraction pattern also affects its magnetic properties. The grain boundaries associated with the columnar structure will pin domains.

13. CONCLUSIONS • Magnetic anisotropy of Py grown directly on Nb is stronger than Py grown on Nb through Cu buffer layer. • Magnetic anisotropy is induced by uniaxial strain due to lattice mismatch between Py and Nb while weakend in samples having Cu buffer layer due to uniaxial stress relaxation in Cu.

14. QUESTIONS??