The physical core is crystallized in magnetic iron-nickel alloy-composite. The core is not hollow.

物质核心是磁性铁镍合金复合材料的结晶，其核心不是中空的。

youdao

The alloy contains 5% nickel and 10% iron.

这种合金含有5%的镍和10%的铁。

youdao

ALLOY steel: a steel containing iron and carbide plus one or more other metals such as nickel, chromium, or molybdenum.

合金钢：指钢中含有铁，碳，以及镍、铬、钼等一种或多种其他的合金元素。

youdao

For instance, while the vast majority of meteorites are stone, almost all sculpturals are made of an iron-nickel alloy, which takes on beautifully complex shapes as it falls to Earth through a process called ablation.

FORBES: Hot Rocks

Both research groups use wire made of a standard alloy of nickel and iron that is easy to magnetise.

ECONOMIST: How to record a memory on a wire