Step 1: Write the field relation.
The magnetic field inside a material is \[ B = \mu_0 (H + M) \] where $H$ is the applied magnetic intensity and $M$ is the magnetization the material develops.
Step 2: Apply the given condition.
The problem says $\mu_0 (H + M) = 0$. Since $\mu_0$ is not zero, the bracket must be zero. \[ H + M = 0 \]
Step 3: Solve for M.
\[ M = -H \]
Step 4: Read the meaning of the sign.
The minus sign tells us the material's magnetization points opposite to the field applied to it.
Step 5: Match to a material type.
Materials that magnetize against the applied field are diamagnetic. They weakly oppose the field.
Step 6: State the answer.
Also $B = 0$ inside, which fits a perfect diamagnet that fully expels the field. \[ \boxed{\text{Diamagnetic}} \]