The basic magnetic properties for Neodymium Iron Boron (sintered) are taken at 20°C. As the temperature is elevated, the values of Br and Hci change. Note that both changes are negative in direction, which means that as the temperature increases, the value of Br and Hci will decrease.
The Temperature Coefficient of Br is given on the product data sheets (see NdFeB – sintered). This is the average rate at which losses are expected. This published data is based on conservative estimates. The data implies that the loss rate is a linear function, however, tests show that this loss is nonlinear. The loss function is difficult to characterize, therefore formulas to predict this behavior has not been developed. The temperature coefficient, however, has been shown to have a correlation to the material’s intrinsic coercivity value at RT.
The graphs below have been put together using three grades of Neodymium Iron Boron. These grades are N3275, N3271 and N3571. These show the relationships of the Br(T) value as a fraction of Br(RT) and Hci(T) value as a fraction of Hci(RT) where

T = Temperature above RT
RT = Room Temperature (20°C)