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Heavy-ions for controlled modification of magnetic thin films
and multilayers
Ajay Gupta
UGC-DAE Consortum for Scientific Research, University Campus,
Khandwa road,Indore-452017
Magnetic thin films and multilayers are an important class of
nanostructured
materials with wide ranging applications in magnetic memory
devices, sensors, high
frequency cores for inductors etc. Heavy ion irradiation has
been an effective tool to
modify the properties of such nanostructures in a controlled
manner. Swift heavyions have several advantages over low energy
ions in terms of depth of modification
and low ion fluences, etc. Various effects induced by heavy ion
irradiation include,
stress relaxation, atomic ordering/disordering, interface
mixing. Specific examples ofboth soft-magnetic (Fe-nitride) as well
as hard-magnetic (FePt, CoPt) films will be
taken in order to demonstrate the use of heavy ions in
controlled modification of their
magnetic properties.
Understanding of the atomic level processes responsible for
these effects is important
from both basic as well as application points of view. Results
will be presented on
the use of some novel x-ray based techniques towards
understanding the heavy ioninduced effects in thin films and
multilayers. i) nuclear resonance reflectivity in
isotopic multilayers [1] has been used to study the irradiation
induced atomic
diffusion of Fe in compositionally homogeneous films of Fe,
Fe-nitride and FePt.The results are being interpreted in terms of
possible mechanism of irradiation
induced atomic motion. ii) In case of multilayers, depth
resolved information about
various phases formed across the interfaces has been obtained
using x-rayfluorescence and XAFS under standing wave conditions
[2]. This information in tern
would be useful in understanding the irradiation induced changes
in the magnetic
properties, as well as the mechanism of the induced changes. A
better understandingof the atomic level mechanisms involved in ion
beam induced modification will help
in a better harnessing of the technique.
[1] Ajay Gupta, Mukul Gupta, Sujoy Chakravarty, Rudolf Rffer,
Hans-ChristianWille, Olaf Leupold, Phys. Rev. B 72 (2005)
014207.
[2] Ajay Gupta, Parasmani Rajput, and Carlo Meneghini, Phys.
Rev. B 76, 195401
(2007); Ajay Gupta, Dileep Kumar, and Carlo Meneghini, Phys.
Rev. B 75 (2007)
064424.
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- stress relaxation
o improvement in soft magnetic properties - FeN
- structural transformation
o amorphization
o order-disordertransformation FePt
- Interface modification
o Variation in interface roughness Fe/Cr
o Interface mixing Fe/Si
- non-equilibrium phase formationo miscible systems
o immissible systems Fe/Ag
- Atomic level mechanism of ion-induced modification
o Irradiation induced atomic motions
Nuclear resonance reflectivity
o Depth resolved structural studies across the interfaces
X-ray standing waves
