Single crystals of undoped and nickel-doped BaFe_(2-x)Ni_xAs_2(x=0,0.04) have been grown by FeAs self-flux method.The maximum dimension of the crystal is as large as ~ 1 cm along the ab plane.The crystalline topography of a cleaved crystal surface is examined by scanning electron microscope(SEM).By x-ray powder diffraction(XRD) experiments using pure silicon as an internal standard,precise unit cell parameters(tetragonal at room temperature) are determined:a = 3.9606(4) A(1 A=0.1 nm),c = 13.015(2) A for BaFe_(1.96)Ni_(0.04)As_2 and a = 3.9590(5) A,c = 13.024(1) A for BaFe_2As_2.DC magnetization and transport measurements are performed to check superconducting transition(T_c=15 K for x=0.04) and other subtle anomalies.For BaFe_(0.96)Ni_(0.04)As_2 crystal,the resistance curve at normal state shows two distinct anomalies associated with spin and structure transitions,and its magnetization data above ~ 91 K exhibit a linear temperature dependence due to spin density wave(SDW) instability. Single crystals of undoped and nickel-doped BaFe_ (2-x) Ni_xAs_2 (x = 0,0.04) have been grown by FeAs self-flux method. The maximum dimension of the crystal is as large as ~ 1 cm along the ab plane. The crystalline topography of a cleaved crystal surface is examined by scanning electron microscope (SEM) .By x-ray powder diffraction (XRD) experiments using pure silicon as an internal standard, precise unit cell parameters (tetragonal at room temperature) are determined: a = 3.9606 (4) A (1 A = 0.1 nm), c = 13.015 (2) A for BaFe_ (1.96) Ni_ (0.04) As_2 and a = 3.9590 (5) A, c = 13.024 (1) A for BaFe_2As_2. DC magnetization and transport measurements are performed to check superconducting transition (T_c = 15 K for x = 0.04) and other subtle anomalies. For BaFe_ (0.96) Ni_ (0.04) As_2 crystal, the resistance curve at normal state shows two distinct anomalies associated with spin and structure transitions, and its magnetization data above ~ 91 K exhibit a linear temperature dependence due to spin density wave (SDW) instability.