Raspberries are different. Do you know what variety you planted?
Where are you located (just generally)? That information always helps us answer more specifically.
So, I wouldn't use any fertilizer-- except manure or compost-- on them until the plants are established. And I wouldn't use MG at all. (This is another subject.) My experience is that it takes 1/2 - 1 year for the plants to establish themselves... and then look out! There will be raspberries everywhere. You may get some berries right away, and possibly more later in the season. But you won't start getting huge numbers until next year.
What you want to do now for your sad looking one-- and I'll defer to the experts who will no doubt come along shortly-- is be sure that the roots have everything they need so new canes will emerge this fall or next
spring (depending on your climate and the variety).
I think what you're seeing is last year's canes (the ones you planted) dying. This is no big deal so long as the roots are doing well. Obviously, you won't get any berries from dead canes, but the plant may send up new canes which might
flower and produce fruit later this season (depending on climate, etc.).
My experience is that raspberries are pretty tough plants. Even if this particular plant dies back to the ground, I'd still make sure the soil is evening moist. And I'd definitely mulch the area with some straw. I"d bet money that it will come back.