Magnetic properties of ordered nanowires of the quasi-two-dimensional antiferromagnet SpFeMn(C$_2$O$_4$)$_3$

Ordered arrays of nanowires of the photochromic antiferromagnet SpFeMn(C$_2$O$_4$)$_3$ (where Sp is 1-$\{$(1',3',3'-trimethyl-6-nitro-5'-chlorospiro[2H-1-benzopyran-2,2'-indolin]-8-yl)methyl$\}$pyridinium) have been fabricated in anodized aluminum oxide pores with diameters of 20 and 200 nm. It has been revealed that the growth of the spin-glass phase with noncollinear ordering of spins in nanowires is suppressed in favor of the uniaxial antiferromagnetic phase. A decrease in the nanowire diameter leads to an increase in the anisotropy of the magnetic resonance spectra. This is associated with the magnetocrystalline anisotropy that considerably exceeds the anisotropy of the nanowire shape.