tokens: generating these artificial leakage parameters, it was ensured that no off-diagonal elements of the Mueller matrix exceeded 1.5 conversion between Stokes parameters at any frequency channel, while reaching this maximum percentage in at least one frequency channel. This limit was chosen based on the following test. From our sample, we chose all pulsars that did not show any RM(φ) variations (e.g. J1048–5832 and J1709–4429). Our assumption was that the imperfections of the receiver could not generate more RM(φ) variations than were already observed. The limit was therefore chosen as the maximum value that did not create additional apparent variations in RM(φ). The systematic uncertainties because of receiver imperfections were quantified for each pulsar by randomly generating 100 receiver imperfections obeying the above description, which then were used to distort the pulsar signal in the process of polarization calibration. 3 For each of these 100 different distortions, we calculated values for RM profile , RM scatt , RM(φ), and Δ( V / I )(φ). The standard deviation of these values was quoted as the systematic uncertainty in Table 1 . The systematic uncertainties determined for the RM(φ) and Δ( V / I ) are displayed for each pulsar, for example in Fig. 1 , in the third and fourth panels as a 1σ contour grey-shaded region overplotted over the RM(φ) values (green in the online version). 4 RESULTS Pulsars described in Sections 4.1 and 4.2 and in Table 1 , for which the phase-resolved RM profile had never been investigated previously in the literature, are marked with an asterisk (*). The plots for the 98 pulsars have been included in the online supplementary material , in Figs A1–A26 and an example is displayed in Fig. 1 . All plots were aligned, so that the total intensity peaked at pulse longitude 180°. For the six pulsars from the sample, which had both a main pulse (MP) and an interpulse (IP), we aligned the MP peak at pulse longitude 90°, and hence the IP peaked around pulse longitude 270°. The results from the analysis described in the Section 3 can be found in Table 1 . The resulting RM(φ) profiles allowed us to classify the pulsars as follows. Pulsars that had were classified as showing significant RM(φ) variations, and they are discussed in more detail, on a case to case basis, in Section 4.1 . Six pulsars, which were initially classified as showing significant RM(φ) variations, were removed from this section based on their high systematic uncertainties. A total of 42 pulsars, of our sample of 98, were classified as showing significant RM(φ) variations. For all cases where we saw RM(φ) variations, we observed deviations from the expected λ 2 dependence (as quantified by , but also by inspecting PA versus λ 2 directly), implying that Faraday law fails to describe the full frequency dependence of the PA, and there must be another frequency and pulse longitude dependent effect present. Therefore, the results obtained from the panel, where
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