Apex domains cannot have CNAME records.
Question and response
Question
dig imicro.com.br. NS
Answer
imicro.com.br. 3 NS minasgerais.imicro.com.br.
imicro.com.br. 3 NS parana.imicro.com.br.
Authority
The response has no authority records.
Additional
minasgerais.imicro.com.br. 3 A 177.131.48.22
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0