-Ni n. Pd m. Pd 1<m<20. Ni 1<n<20. System. e-beam evaporation. Deposition Technique. P=10-8 Torr, T=400 K 30 nm Pd/ 5 nm Pd.

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1 Department of Physics, Aristotle University of Thessaloniki, 54 6 Thessaloniki-Greece Study of the Magnetoresistance Mechanisms in Pd - Ni multilayer system M. Angelakeris and N.K. Flevaris

2 Outline Introduction Sample Preparation Structure & Magnetic Profile Electrical Measurements Experimental Data Analysis Summary - Conclusions

3 Introduction Magnetic multilayers:key configurations in Magnetoelectronics Utilization of unique micromagnetic, magnetooptic magnetoelectronic phenomena which cannot be realized on the basis of conventional materials Interesting phenomena arising from: surface/interface effects, low-dimensional properties, p coupling Anisotropic Magnetoresistance effect (AMR) is a galvanomagnetic g mechanism known for more than 14 years Prototype hard disks heads based on AMR thin films Relation between microstructure, magnetism & electrical transport Giant or Anisotropic magnetoresistance?

4 Sample Preparation Pd-5nm System Deposition Technique Pd m -Ni n e-beam evaporation Pd-3nm Parameters buffer / overlayer mica Substrate mica P=1-8 Torr, T=4 K 3 nm Pd/ 5 nm Pd Pd 1<m<2 Ni 1<n<2 Total Thickness Structure 2-4 nm θ-2θ XRD, TEM

5 Structure & Magnetic Profile - 1 epitaxial growth [111] direction small-angle grain boundaries double-positioning & embedded twinning wavy form no columnar growth non monotonic dependence on m,n for short wavelengths structural modification & interlayer coupling

6 Structure & Magnetic Profile - 2 M (emu/ /cm 3 -Ni) 1 Pd m -Ni 2 m T=1K H (Oe) M S : 5-7% m increase Development of PMA

7 Structure & Magnetic Profile - 3 m=6 - n=3,6 1. n dependence finite size 9.9 effects Τ C reduction K) M s (T)/M M(T=.8 m-n m=2,3,6 -n= n=3 Θερμοκρασία Temperature (K) m dependence interlayer Coupling

8 Structure & Magnetic Profile - 4 Aniso otropy, Magnetiza ation Anisotrop py (erg/cm 3 )x 1 6 Pd 4 -Ni 2 8 (a) K eff M S 2πΜ 2 K u1 (b) Temperature (K) Κ=Κ - 2πM 2 u1 S u1 K u1 max values M S variation 36% Shape anisotropy~ M 2 S K u1 ~ M 3 s S

9 Electrical Measurements ρ Τ ρ // ρ Experimental setups st : ramping applied field at fixed angle 1 st 2 nd : rotation of constant field ρ // ρ - ρ // ρ Τ - ρ ρ Τ Δρ/ρ% / % =[ρ(,t) - ρ(,t)]/ ρ(,t)

10 Electrical Measurements Experimental 1 PdNi 2 -Ni 2, Pd Pd2-Ni2 2 -Ni 2 MR ρ // ρ T,8 MR,18,12,6 Pd2-Ni2 2 2 Pd 2 -Ni 2 2 -Ni ,5 5 5, ,4 H (Tesla).5 1 ρ // ρ -, Angle ( o )

11 Electrical Measurements Experimental 2 Δρ/ρ ρ % m=n LN2 Temperature Room Temperature 1 Mrem m/ms,5 m=n T=3 K m (number of atomic layers) 1 Hs (O Oe) 1 1 m=n T=3 K m (number of atomic layers) m (number of atomic layers)

12 Electrical Measurements Experimental 3-3 (Δρ/ρ ρ)sat x Pd Series3 2 -Ni 2 Pd Series1 3 -Ni 3 Pd Series4 4- Ni 4 Pd Series2 1 -Ni 1-2 2,2 4,4 6,6 8,8 1 cos 2 θ -4-6 ρ(θ) ) =ρ ρ + Δρ cos 2 ΑΜR Θ Δρ ΑΜR =ρ // - ρ

13 Electrical Measurements Data Analysis 1 AMR ra atio 2,3 21 2,1 1,9 ρ) per (Δρ/ρ) par +(Δρ/ρ 2,5 2,4x1-2 Pd 3 -Ni 3 Pd -Ni 2 2 2,x1-2 Pd 4 -Ni 4 Pd 8 -Ni 8 1,6x1-2 1,2x1-2 8,x1-3 4,x Temperature(K) 1,7 1,5 13 1,3 Pd2-Ni2 Pd3-Ni3 Pd4-Ni4 Pd8-Ni T (K) AMR=Δρ/ρ av, Δρ=ρ // - ρ ρ av av =1 /3 ρ // // + 2 /3 /3 ρ

14 Electrical Measurements Data Analysis 2 12,5 ρ(τ=)-m ρ = ρ ο (c) + ρ el-ph ph(τ) + ρ m (Τ,Η,θ) m (μω Ω x cm) ρm 12,3 Pd 4 -Ni ,11 Pd 3 -Ni 3 Pd 1 -Ni 1 11,9 1 2 Pd 3 -Ni 2 m=n 8 Pd 2 -Ni 1 Pd 4 -Ni 2 Pd 4 2 -Ni T (K)

15 Electrical Measurements Data Analysis ,8 6,6,4, , ,5 1, Pd 1 -Ni 1 -,2 -,4 -,6 -, , , ,5 1,5 21-1, ,5 27 Pd 3 -Ni , ,5 33 Pd 2 -Ni ,5 27 3

16 Summary - Conclusions Anisotropic magnetoresistance was studied via two experimental setups in Pd-Ni multilayer system in correlation with structure and magnetic features. A simple model to isolate the magnetic term from the over-all electrical resistance is proposed. Size effects seem to play an important role to overall electrical response of multilayer systems. Interface/bulk scattering mechanism becomes dominant by adjusting modulation parameters. The optimization of anisotropic magnetoresistance may be achieved and tailor made electric response materials may be fabricated. Acknowledgements Dr. J.B.Soussa and Dr. St.Visnovsky for the provision of MR Measuring Facilities Work is supported by the HPRN-CT CT EU contract