Effect of hydrogenation on the magnetic and magnetoelastic properties of R 2Fe14B compounds (R = Nd, Gd, Er, Lu)

The temperature dependences of the magnetization σ(T), magnetostriction λ(T), and linear thermal expansion coefficient α(T) of R ₂Fe₁₄B intermetallic compounds (R = Nd, Gd, Er, Lu) and of their hydrides R ₂Fe₁₄BH_2.5 are studied. The magnetization was measured with a pendulum magnetometer within the temperature interval 77–700 K in a magnetic field H = 500 Oe. Magnetostriction and thermal expansion were measured using the tensometric technique in the temperature interval 77–420 K. It was established that Gd₂Fe₁₄BH_2.5 undergoes a spin-reorientational (SR) transition at T _SR = 235 K. In compounds with Nd and Er, anomalies associated with the SR transition were found in the σ(T), λ(T), and α(T) curves. The SR transition temperatures were refined and magnetic phase diagrams were constructed for the compounds studied. The α(T) curves of the R ₂Fe₁₄BH_2.5 hydrides (R = Nd, Er) revealed anomalies of a nonmagnetic origin associated with hydrogen ordering in the crystal lattice of these compounds.