Ni-Mn-Ga Heuslers show the magnetic shape memory effect and are finding their way into various applications. They owe their properties to the high twin boundary mobility in the 5M modulated tetragonal martensitic state, which is the stable state at room temperature in the Ni50Mn25Ga24 composition according to x-ray diffraction experiments. The drawback is that at lower temperatures, an intermartensitic transition to the 7M modulated state and eventually to the L1_0 state can occur which may not be reversible so that its reusage at room temperature can be hampered. This is particularly relevant for space technology or other extreme conditions where temperatures can easily reach intermartensitic transition temperatures. It is therefore important to understand the details of the presence and stability of the various phases to be able to recover the favorable 5M state on cycling the temperature. We aim to investigate the properties of the intermartensitic phase transitions as a function of temperature down to 5 K to examine the details of the structure in the ground state and how this ground state reverts to the 5 M state on rewarming to ambient temperature or by a magnetic field.