Anisotropy of exchange interactions and spin reversal in the compensated ferrimagnet <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>Ni</mml:mi><mml:mn>4</mml:mn></mml:msub><mml:msub><mml:mi>Nb</mml:mi><mml:mn>2</

Spin reversal and magnetization hysteresis loop were studied in the mean-field approximation for the anisotropic model of the compensated ferrimagnet <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:mrow><a:msub><a:mi>Ni</a:mi><a:mn>4</a:mn></a:msub><a:msub><a:mi>Nb</a:mi><a:mn>2</a:mn></a:msub><a:msub><a:mi mathvariant="normal">O</a:mi><a:mn>9</a:mn></a:msub></a:mrow></a:math>. A rigorous analysis was applied to determine the energy of exchange anisotropy in the <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"><c:mrow><c:mi mathvariant="italic">ab</c:mi></c:mrow></c:math> plane. Based on the experimental data on the single crystal [], the values of the main parameters of microscopic interactions were obtained. This made it possible to calculate the temperature dependence of magnetization, showing spin reversal, as well as the magnetization hysteresis loop, demonstrating the exchange bias. A good qualitative agreement between the experiment and theory was obtained. The effect of single-ion anisotropy on the magnetism of nickel niobate was analyzed and the importance of the contribution of antiferromagnetic exchange interactions with the second nearest neighbors to the stable ferrimagnetic state of the crystal is presented.