For 10 points, name this layer that is surrounded by the outer core.
The three translational oscillations of this region are called the Slichter triplet. The anisotropy of this region was studied using PKIKP travel times. Discovered by Inge Lehmann, this region has a radius of about 1200 kilometers and a temperature comparable to the Sun's surface. This region is located below the layer that is responsible for Earth's magnetic field. This solid layer primarily consists of a nickel-iron alloy. For 10 points, name this layer that is surrounded by the outer core.
The three translational oscillations of this region are called the Slichter triplet.
{inner core} [prompt on "core"]