Spin-glass behavior and zero-field-cooled exchange bias in a Cr-based antiperovskite compound PdNCr3

Abstract

We report the synthesis, structure, and magnetic and electrical/thermal transport properties of a Cr-based antiperovskite compound PdNCr₃, which crystallizes in MgCNi₃-type cubic structure (space group Pmm, No. 221). Interestingly, the spin-glass (SG) behavior, which is confirmed by the corresponding characteristic parameters (the freezing temperature T₀ = 61.4(2) K, the dynamical exponent zν = 7.103(3), and the flipping time τ₀ = 2.714(2) × 10⁻¹¹ s), is observed in PdNCr₃. Furthermore, the value of the Sommerfeld–Wilson ratio (R_W ∼ 1.024(3)) for PdNCr₃ is much smaller than those of cluster glass systems (R_W > 100) and Kondo cluster glass systems (R_W = 20–30), indicating that PdNCr₃ is a canonical SG system. Density functional theory calculation shows that the origin of SG in PdNCr₃ is attributed to the disordering located N vacancies, which is further confirmed by the measurement of sample PdN_0.75Cr₃ with more N deficiency. On the other hand, infrequently, the zero-field-cooled exchange bias (ZFC-EB) with an exchange bias field (H_E) of about 350 Oe is observed after zero-field cooling from an unmagnetized state in PdNCr₃. The values of H_E are found to depend strongly on temperature and measuring magnetic field. For PdNCr₃, the ferromagnetic unidirectional anisotropy, which is the origin of our ZFC-EB effect, is formed around the ferromagnetic–SG interface isothermally during the initial magnetization process below the blocking temperature. In addition, the training effect of ZFC-EB in PdNCr₃ is observed after the zero-field cooling process and has been explained well in terms of the spin configurational relaxation model.