Low-temperature phase transitions in magnetically ordered neodymium

Single-crystal neodymium samples are investigated by using X-ray diffraction technique in the temperature interval between 4.2 and 300 K. The results provide new information on the temperature dependence of the lattice parameters a and c of a double hexagonal closely packed structure and about linear thermal expansion coefficients α⊥ and α∥. The observed anomalies on these temperature dependences at TN1 = 20 K, TN2 = 7.8 K and T0 = 6.5 ± 0.2 K are due to antiferromagnetic ordering. It is shown that magnetic transformations at TN1 and TN2 are second-order phase transitions, while a first-order phase transition occurs at T0. Neodymium exhibits sharp anomaly in thermal expansion in the paramagnetic region 20–50 K due to the splitting of the 4f-levels by the crystal field (Schottky anomaly).

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