Answer: I'm sorry you had trouble with your tree. Magnolias need a soil that is acidic, organic and humusy, and evenly moist yet well drained. They also need a spot with protection from winter winds, and also have a dense, fine root system throughout the area beneath the branches, so magnolia might not be the best choice for your planting site.
Commercial topsoil is unfortunately not a regulated material, so depending on the soil you used for your raised bed, it may not be suitable, for instance it may not have been acidic enough or humusy enough. Whenever you have a new tree that fails to thrive, it is a good idea to consult with your professionally trained nurseryman early on and see if the tree can be saved -- or at least determine why it is not doing well.
There is also a possibility that the raised soil does not mesh well with the native soil below it, thereby creating a drainage problem. This could happen for example if the top layer is clay-based while the lower layer is gravelly. Your professional nursery staff should be able to help you test and analyze the soil to make sure it is going to be able to accommodate your new tree.
It is usually better to plant a tree that is suited to the native soil conditions rather than to try to amend the soil -- any substantial changes will require ongoing effort to maintain, and tree roots usually extend well beyond the branch spread of the mature tree. So, depending on the test results, you may even want to undo or amend the raised bed.
A raised bed is typically well drained, so again you will need a tree that can handle that (assuming your soil tests that way). You might look at -- as you mentioned -- the hawthorns (thorny to work under and check local disease prevalence), newer disease resistant crabapples (many sizes and flower colors available), and also redbuds (a terrific native tree, but not terribly long lived), or the mountain ash (again check local disease prevalence, as it is susceptible to fireblight). You might also consider the Japanese tree lilac, Syringa reticulata.
Keep in mind though that any tree will compete with the plantings below it for both moisture, nutrients and also sunlight. The surrounding plants can also set back the new tree's root growth during the establishment phase. For this reason you may want to consider planting a groundcover or leaving a mulched area beneath the tree. Your local professional nursery staff should be able to help you analyze growing conditions and select something suitable and within your size requirements.
Good luck with your new tree!
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