Effect of Ce substitution on the local magnetic ordering and phonon instabilities in antiferromagnetic DyCrO₃perovskites

A detailed crystal structure analysis, temperature and field dependence of magnetic characteristics and phonon instabilities for different compositions (0.1 ⩽x⩽ 0.5) of Dy_1-xCe_xCrO₃solid-solutions have been reported. All the investigated compounds exhibit distorted orthorhombic crystal structure with a distortion factor ofd_Oct/d_Cell∼ 6 × 10^-3/3.5 ppm (forx∼ 0.2) forPbnmspace group that follows Vegard's law. The bonds between apical oxygen atoms (O_A1) and Cr atoms stand more rigidly in comparison with the basal oxygen atoms (O_B1/O_B2) resulting the octahedral distortion and thereby causing the changes in phonon modes. The CrO₆octahedral tilt angleθrotates with respect to the Miller pseudocubic axis [101] which varies from 10.36° (x= 0.1) to 12.25° (x= 0.5) and significantly influences the A_g(5) phonon stability by 3% for a change in A-site mean radius from 1.095 Å to 1.141 Å forx= 0.1 and 0.5, respectively. From the magnetization measurements we find that these series of compositions exhibit canted antiferromagnetic (AFM) ordering with Néel temperature,TN1that increases from 151.8 K (x= 0.1) to 162 K (x= 0.5) which also manifests as a significant reduction in the magneto-crystalline anisotropy (H_K∼ 2.58 kOe → 2.07 kOe,K₁∼ 36.47 J m^-3→ 18.97 J m^-3) while maintaining the stable Γ₄(G_x,A_y,F_z) AFM configuration. Both Dzyaloshinskii-Moriya interaction method and modified Curie-Weiss law are employed to analyse the inverse paramagnetic susceptibility,χ^-1(T>TN1). Further, we have evaluated the symmetric (J_S) and antisymmetric exchange (D_AS) constants, which show progressively increasing trend (J_S→ 10.08 K to 11.18 K andD_AS→ 1.24 K to 1.73 K) with the incorporation of Ce inside the perovskite lattice. Furthermore, the role of Ce substitution on the low-temperature spin reorientation transition (T_SR∼ 3.5 K → 16.8 K pertaining to the Γ₂₅phase configuration) and emergence ofΓ2(Fx,Cy,Gz;FxR,CyR)weak-FM phase between 31 K and 45.5 K are discussed in consonance with the phonon spectra.