File Name is incorrect in Directory

This is my test.

x = 1.;
file2 = "sqrt2_2b.txt";
Do[x = x/2 + 1/x; x >>> file2, {5}]

This code above I get the File name “file2”. However, this code below will give me the name I want.

x = 1.;
Do[x = x/2 + 1/x; x >>> "sqrt2_2b.txt", {5}]

This will give File Name “sqrt2_2b.txt”.

Why is this? Could anyone explain this phenomenon?