Itinerant Magnets and Magnetocalorics

Magnetic refrigerants, spin-frustrated systems, and helimagnets
This research is supported by the National Science Foundation (DMR-1507233)

Research in solid-state chemistry and magnetism.

Figure 1. Research in solid-state chemistry and magnetism.

The central focus of this project is on the magnetic and structural properties of rare-earth cobalt phosphides with the ThCr2Si2-type structure (Fig. 1). While ternary phosphides RCo2P2 (R = La, Ce, Pr, Nd, Sm) show rather simple magnetic behavior,1 quaternary phases La1-xPrxCo2P2 exhibit multiple magnetic transitions, leading to the observation of such interesting phenomena as metamagnetism and magnetic pole reversal.2,3 The ferromagnetic transition temperature of LaCo2P2 (TC = 132 K) is dramatically raised upon substitution of R for La, reaching almost room temperature for La0.12Pr0.88Co2P2 and La0.25Nd0.75Co2P2 (Fig. 2). This is in drastic contrast to the isostructural La1-xRxMn2E2 (E = Si, Ge) phases,4 in which the ferromagnetic transition remains essentially unaffected by the substitutions in the rare-earth sublattice.

The increase in the ferromagnetic ordering temperature can be rationalized by the analysis of the calculated spin-polarized density of states, which reveals a larger difference in the population of the majority and minority spin subbands for the higher R content.2 This leads to stronger intralayer exchange interactions between the Co centers. The observed magnetic and structural properties prompt investigation of the rare-earth cobalt phosphides under high applied pressure and/or magnetic field, which might lead to detection of new magnetic and/or structural transitions. The exact nature of the observed magnetic ordering will be probed with neutron diffraction and XMCD, experiments that are currently underway.

References

  • 1. Tan, X.; Tener, Z. P.; Shatruk, M. Correlating itinerant magnetism in RCo2Pn2 pnictides (R = La, Ce, Pr, Nd, Ca; Pn = P, As) to their crystal and electronic structures. Acc. Chem. Res. 2018, 51, In press.
  • 2. Shatruk, M. Chemical aspects of itinerant magnetism. In Encyclopedia of Inorganic and Bioinorganic Chemistry, Scott, R. A., Ed.; Wiley-VCH: Chichester, 2017.
  • 3. Tan, X.; Fabbris, G.; Haskel, D.; Yaroslavtsev, A. A.; Cao, H. B.; Thompson, C. M.; Kovnir, K.; Menushenkov, A. P.; Chernikov, R. V.; Garlea, V. O.; Shatruk, M. A transition from localized to strongly correlated electron behavior and mixed valence driven by physical or chemical pressure in ACo2As2 (A = Eu, Ca). J. Am. Chem. Soc. 2016, 138, 2724-2731.