From the applications point of view, the advantage of the very low density of MgB2 bulk samples must be taken into consideration and, the generation of strong magnetic flux densities using MgB2 should be investigated [1]. In this contribution, we have studied the trapped magnetic field properties of samples of 20 mm, 40 mm and 50 mm in diameter. Samples with a diameter of 20 mm and 40 mm were processed by ex-situ Spark Plasma Sintering, since the sample of 50 mm of diameter, from Edison Spa, has been produced using a Reactive Mg-Liquid Infiltration process. Both processes are able to produce dense and high quality MgB2 samples. For the sample of 40 mm diameter, some Field Cooling experiments were carried out at temperatures from 10 K to 30 K both on a single pellet of 4 mm high and on a stack of several pellets of the same diameter. With the help of modeling tools, we have simulated the behavior of such samples in order to deduce their parameters as Jc(B) and n-value, Fig. 1. With these simulations and experiments, we will show that the most relevant parameter for the applications of large-sized bulk MgB2 samples as permanent magnet is the irreversibility field Hirr and not the critical current density at zero field Jc(0). Fig. 1: Two models of critical current density (a), and the simulated resulting trapped magnetic field at the center of the surface of a bulk MgB2 of 20 mm of diameter and 4 mm high (b). References 1. J. G. Noudem, M. Aburras, P. Bernstein, X. Chaud, M. Muralidhar, and M. Murakami, Development in processing of MgB2 cryo-magnet superconductors, J. Appl. Phys. 116, 163916 (2014).