Magnetic properties of hydrides of the rare earths and rare earth intermetallics

Abstract

Rare earth elements (R) react with hydrogen at elevated temperatures to form hydrides with compositions approaching RH₃. Intermetallic compounds involving the rare earths in chemical union with Mn, Fe, Co or Ni absorb copious quantities of hydrogen rapidly and dissociatively at room temperature. In all the hydrides RH₃ and in many of the hydrogenated intermetallics the proton density exceeds that in condensed elemental hydrogen. The presence of such large amounts of hydrogen significantly modifies various physical properties of the host metal. In the elemental rare earths hydrogenation produces a loss in metallic conduction and greatly weakens exchange. Magnetic ordering is suppressed by as much as 250 degrees. In contrast hydrogenation of intermetallics may either strengthen or weaken exchange, the latter predominating numerically in the systems studied to date. Contrasting behavior is exhibited by the isostructural pair of compounds Y₆Mn₂₃ and Th₆Mn₂₃. Th₆Mn₂₃ exhibits Pauli paramagnetism whereas Y₆Mn₂₃ is ferromagnetic. Hydrided Th₆Mn₂₃ and Y₆Mn₂₃ are ferromagnetic and paramagnetic, respectively. The weakening of exchange in RH₃ is a simple consequence of the depopulation of the conduction band to form anionic hydrogen. Elucidation of the magnetic behavior of the hydrided intermetallics requires detailed band structure information, which is non‐existent at present.