2.7.1. The Problems of the Proper Sample Preparing for Magnetic Measurements

At first, we solved the problems of incorrect mounting of the sample. The example of such problematic measurement due to improper sample mounting could be seen in Figure 3a. A sample (103 mg) of the fresh liver of 7-week WKY rat was inserted into standard capsule used in magnetic measurements, and the capsule was fixed by cotton into the straw. *M*(*H*) curve was measured at 300 K. A reciprocating sample option (RSO) was used with a scan length of 4 cm through the 2nd order gradiometer, and the number of averaged scans per measurement was 5. The centring procedure was performed by application of the small magnetic field. The magnet was not quenched, so the start of the measurement was with non-zero magnetisation (Figure 3a, point A). Scan through the gradiometer and voltage output are shown in Figure 3b. Relatively good voltage output was obtained. As the field was increasing (Figure 3a, point B) the magnetisation was changed to the negative values and this way, it was fitted by the MPMS (Figure 3b). Then the maximum field was reached (Figure 3a, point C), this leads to a good fit of the output voltage (Figure 3b) but with unbalanced output on the borders (maximum at 0.5 and 3.5 cm). This unbalanced output results from the position of the sample in capsule and from the cover of capsule and cotton. Then the field decreased to the point D, and its voltage output (Figure 3c) was not properly fitted, giving positive voltage fit of the curve from the sample holder instead of negative one from the sample alone. These false measurements added a hysteresis to the measured *M*(*H*) curve. Point E showed (Figure 3a) no problem with fitting at all, the signal from the sample mounting is again neglected, due to higher output of the sample alone (voltage outputs at the points C and E were rescaled down to be shown with the other signals). There is also a visible problem with sample instability, as the water from the sample was evaporating, the final point of *M*(*H*) curve was not overlapping with the point C.

Unsuitable sample holder could also affect the measurement of the temperature dependence of the magnetisation (Figure 4a). When the mass magnetisation goes close to zero, there is significant "jump" to the opposite value, for both ZFC and FC curves. In some cases, the presence of sudden changes in the values of the magnetisation could be observed for higher applied magnetic field too (Figure 4b). Here, the heart from a 9-week old WKY rat was measured. Another example of improper use of a capsule as a sample holder is in Figure 4c. Corrupted measurement occurs in the low magnetic field region, but the overall appearance of the curve is acceptable.

**Figure 3.** (**a**) *M*(*H*) dependence of the fresh sample of the liver of Wistar-Kyoto (WKY) rat, (**b**) the voltage output of longitudinal SQUID scan for marked points (A–C) of the *M*(*H*) dependence presented in Figure 3a, (**c**) the voltage output of the longitudinal SQUID scan for marked points (D–E) of the *MH* dependence shown in Figure 3a.

**Figure 4.** (**a**) Temperature dependence of the mass magnetisation of the same sample as in Figure 3, (**b**) *M*(*H*) dependence of the WKY rat heart at 300 K, (**c**) *M*(*H*) dependence of WKY rat liver at 300 K.
