As and Epitaxial-Growth MnSi Thin Films - OPUS Würzburg

78 6. Epitaxial Growth of MnSi Thin Films
400
350
Resistivity(mΩ-cm)
300
250
200
150
100
0 10 20 30 40 50 60 70 80 90 100
Temperature (K)
Fig. 6.9: Resistivity plot against temperature for the 20-nm thin layer. The resistivity curve
(black) was fitted with a parallel resistor equation at T > Tc (red) and a power law at T <
Tc.([Mena 03]) The exponent for the power law dependence of the resistivity at below Tc is
calculated ≈ 2.0 for the 20-nm layer, which fits the expected Fermi liquid behavior.
T c of the resistivity curve. This is usually identified as the transition region between the
helical-paramagnetic phase in bulk samples.[Petr 06] An average of T c ≈ 40K is observed
for both films, consistent with values reported in [Karh 10] and [Li 13]. A summary of
the measured residual resistivity ratios, to see crystalline quality in the grown films, is
shown in Table 6.3.
Residual Resistivity Ratios
Thickness ρ 300K /ρ 4K
12 nm 13
20 nm 6 - 7
Tab. 6.3: Measured RRR values for the films measured in this work. The value for the the 12
nm layer is similar to the reported values from [Li 13] for their 10 nm layers, which suggest at
least good crystalline quality for the thinner layer.
Theexperimentalcurvewasfittedwithtwodifferentformulasforthedifferenttemperature
ranges, asinMena et. al.([Mena 03])Theredcurve represents thetemperature-dependent
power-law fitting to the electrical resistivity starting at base temperature (4K) until T ≈
30: ρ(T) = ρ(0) + AT µ , with calculated fitting parameters ρ(0) = 166.2 µΩ-cm, A = 0.22
µΩ-cm-K −1 and µ = 2.0. The factor approximates well the Fermi liquid T 2 -dependence