Thickness Dependent Interlayer Magnetoresistance in Multilayer Graphene Stacks

Figure 3

Interlayer magnetoresistance observed in weakly coupled MLG samples with various thicknesses. Data from (a) ~60 nm (batch S1), (b) ~200 nm (batch S2), and (c) ~300 nm (batch S3) samples are shown. At 50 K (Figure (a)), CPP resistance sharply drops with increasing magnetic field above  kG and exhibits negative MR of ~40%. The negative MR effect becomes weaker as temperature is increased. For thicker MLG sample (Figure (b)), the negative MR is stronger, ~92% at 50 K. For samples with even larger thickness (Figure (c)), often exceeds the upper limit (100 MΩ) of the measurement apparatus, behaving as a virtual open circuit. However, as the perpendicular magnetic field is increased, resistance drops drastically by several orders of magnitude, resulting in a giant negative magnetoresistance that reaches theoretical maximum of ~100%. For all three sets of samples, average of both scan directions is presented at each temperature and no hysteresis has been observed. Each resistance value is the average of 50 readings. A constant DC current of 1 mA is applied to perform all MR measurements. The measured resistance values have been validated by using two different setups (Picotest multimeter and Keithley source meter). The insets in (a) and (b) show versus , and clear linear fits have been observed, which is consistent with the ILMR model. The top inset in Figure (c) shows magnetic field dependent switching of the I-V characteristics at various temperatures for the 300 nm sample. (d) MR ratio () as a function of MLG thickness of as-grown MLG on Ni samples at 50 K. The magnetoresistance ratio increases with the thickness of MLG stack and almost reaches theoretical maximum (~100%) for thickness larger than 300 nm. Bottom inset shows data from a 300 nm thick sample which exhibits measurable finite of ~10⁷ Ω. The MR data point corresponding to 300 nm thickness value in the main image is taken from this plot. The top inset shows versus for the three batches. For 25 nm and 300 nm data points, error bars are smaller than marker size.

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