2.7.2. Polyethylene Holder for Powder and Liquid Samples

Considering all the problems and restrictions in the sample preparation for the magnetic measurement, the plastic sample holder (Figure 5) was developed. It is created from high-density polyethylene (HDPE; specification: ultra-high molecular weight polyethylene, Tivar 1000 natural, developed by Quadrant EPP (now Mitsubishi Chemical Advanced Materials Composites, Nitra, Slovakia)). This material shows a relatively small change of magnetic properties with the temperature in the range of 2–300 K, the diameter of the holder is 6 mm and the length of 210 mm was chosen to be as long as a standard plastic straw for MPMS with the end caps. These dimensions were chosen to minimise the weight, possible problems with thermal stability and to minimise the time needed for changes in temperature during cooling and heating. According to [29], the sample space was chosen to be 3 mm in diameter and 5 mm of length.

**Figure 5.** Schematics of high-density polyethylene sample holder configuration.

If the sample holder was without a cavity for the sample, its length ensures that no signal is created on the output of 2nd order gradiometer. HDPE is diamagnetic, so the cavity for the sample creates proportional signal to its dimensions, but with reciprocal value attributable to paramagnetic material. Magnetic properties of this sample holder with a cavity filled with He gas to minimise the possible paramagnetic output of air are in Figure 6.

**Figure 6.** (**a**) The temperature dependence of the magnetic moment for presented plastic sample holder with the cavity filled with He gas measured at 5 mT (left axis) and 1 T (right axis) and (**b**) the magnetic field dependence of the magnetic moment for presented plastic sample holder measured at 2 and 300 K.

The measured data show a strong dependence of the magnetic moment of the cavity on temperature, mainly below 50 K. There is a need to measure corrections for each sample holder before measurement of the samples, which should be later subtracted. The sample holder proved to be temperature stable during measurements, so there is no visible shift in position in the temperature range from 1.8 to 350 K. It is used for measurement of the powder samples and liquids. When measuring such samples, one should be aware of the evaporation of liquid samples during long measurements, as there is often significant change in the magnetic moment of the sample.
