Temperature-dependent magnetic depth profiles of epitaxial films with graded and oscillatory exchange coupling structure
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Temperature-dependent magnetic depth profiles of epitaxial films with graded and oscillatory exchange coupling structure
CIC nanoGUNE Seminars
- Speaker
-
Lorenzo Fallarino, Nanomagnetism Group
- When
-
2016/09/05
13:00
- Place
- nanoGUNE seminar room, Tolosa Hiribidea 76, Donostia - San Sebastian
- Add to calendar
-
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Precise tailoring of magnetic interfaces allows for the control of exchange
coupling strength and effective Curie temperature ( _T C_) over tens of nm
[1]. In this regard, Cobalt-Chromium alloys, Co1- _x_ Cr _x_ , constitute an
interesting model system having magnetic properties that are easily tunable by
changing the dopant concentration _x_. We have grown a series of graded
Co/Co1- _x_ Cr _x_ /Co (10-10) epitaxial thin films on top of a
Si(110)/Ag(110)/Cr(211) template structure, with _x_ having an overall
U-shaped concentration profile. The structural XRD analysis verifies the
epitaxial nature and crystallographic quality for the entire set of samples,
with in-plane c-axis orientation. Temperature and field-dependent magnetic
depth profiles have been measured using polarized neutron reflectometry (PNR).
The effective _T C_ is found to vary as a function of depth, exhibiting a
minimum in the center of the structure, verifying the graded modulation. The
coupling in between the two outer Co layers results dependent on the
magnetization of the central Co1- _x_ Cr _x_ spacer, and thus continuously
tunable via temperature T. For _x c _= 0.28, magnetometry measurements reveal
square hysteresis loops below 260 K, which change to a two-steps loop behavior
for higher temperatures, suggesting an abrupt transition from coupled to
uncoupled behavior. We have therefore studied the temperature dependence of
the magnetization reversal process via PNR for this sample, measurements that
confirm the magnetic decoupling of top and bottom sample parts at elevated
temperatures. In addition to this U-shaped concentration profile, we have
explored an “oscillatory effective Curie temperature†structure of
different wavelength l produced by a triangular Cr content profile,
oscillating in between _x_ = 0.22 and _x_ = 0.28. PNR data prove the
achievement of the desired oscillatory pattern and by changing l, we have
explored the viability of compositional effects being transferred into
modulated magnetic states.
[1] B. J. Kirby, H. F. Belliveau, D. D. Belyea, P. A. Kienzle, A. J.
Grutter, P. Riego, A. Berger, and Casey W. Miller, Phys. Rev. Lett. **116** ,
047203 (2016).