Electronic structure of GdNi and HoNi

Equiatomic GdNi and HoNi are ferromagnetic materials with a Curie temperature Tc= 69 K and Tc =36 K, respectively. These compounds exhibit a large magnetocaloric effect and are suitable for low temperature magnetic refrigerator applications. We investigate the electronic structure of GdNi and HoNi using Hard hard X-ray photoemission spectroscopy (HAXPES). HAXPES of the Gd and Ho 3d, 4d, 4s and 5p core level spectra confirm the atomic multiplets of Gd³⁺ and Ho³⁺. Valence band HAXPES of GdNi and HoNi shows Ni 3d features at the Fermi level, confirming a partially filled 3d band, while the Gd 4f/ Ho 4f states occur at high binding energies away from the Fermi level. For GdNi, we have also carried out XAS and XMCD studies in the ferromagnetic phase at T = 25 K. We analyze the Gd M_4,5-edge and Ni L_2,3-edge spectra using atomic multiplet and cluster model calculations, respectively. The Gd M_4,5-edge XMCD spectrum is consistent with a ground state configuration of S = 7/2 and L=0. The Ni L_2,3-edge XMCD results indicate that the antiferromagnetically aligned Ni moments exhibit a small but finite magnetic moment ( m_tot ∼ 0.19 μB ). The results indicate that the Ni 3d band is not fully occupied and invalidates the charge-transfer model for GdNi and HoNi.