Synthesis and study of transport and magnetic properties of magnesium cage compounds RNi2Mg20 (R=Pr and Nd)

• Published in: Journal of alloys and compounds 2022-02, Vol.894, p.162361, Article 162361
• Main Authors: Kusanose, Yuka, Onimaru, Takahiro, Yamane, Yu, Umeo, Kazunori, Takabatake, Toshiro
• Format: Article
• Language: English
• Subjects: Cage compounds; Cooling; Crystal growth; Electrical transport; Energy gap; Ferromagnetism; Heat capacity; Magnesium; Magnetic measurements; Magnetic permeability; Magnetic properties; Phase transitions; Praseodymium; Rare earth alloys and compounds; Short range order
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2021.162361

•Synthesis of polycrystalline sample of a new magnesium cage compound PrNi2Mg20.•Lattice parameters of RNi2Mg20 (R=Pr and Nd) much larger than those of RT2X20 (T: Transition metal, X = Al, Zn, Cd).•Van-Vleck-like paramagnetic behavior in PrNi2Mg20 and contrasting Curie-like one in NdNi2Mg20.•Confirmation of the nonmagnetic doublet ground state in PrNi2Mg20 carrying quadrupolar degrees of freedom.•Ferromagnetic order of a Kramers doublet in NdNi2Mg20, above which magnetic fluctuations partly lift the doublet. We have synthesized magnesium cage compounds RNi2Mg20 (R=Pr and Nd). We report the measurements of electrical resistivity ρ, magnetic susceptibility χ, isothermal magnetization M, and specific heat C. Polycrystalline samples with R= Pr and Nd were obtained by annealing, while the counterparts for R= La, Ce, and Y were found to be absent. The ρ(T) data for R= Pr and Nd monotonically decrease on cooling from 300 K to 40 K and exhibit shoulders at around 13 K and 15 K, respectively. The Curie–Weiss behaviors of the χ(T) data indicate the trivalent states of both the Pr and Nd ions. For R= Pr, the maximum in C(T) at around 7 K is reproduced by a doublet-triplet two-level model with an energy gap of 14 K. The peak in C(T) at 0.7 K is attributed to a short-range order of quadrupolar degrees of freedom in the non-Kramers ground doublet. On the other hand, for R= Nd, a maximum in C(T) at around 9 K is explained by thermal excitation from a ground state doublet to an excited quartet separated by 23 K. Upon further cooling, C(T) shows a lambda-shaped peak at 1.5 K. By applying magnetic fields up to 2 T, the peak becomes broad and shifts to higher temperatures, which is a characteristic of a ferromagnetic order.