$line = 'Iteration {Applied Field}  {Total Energy}    Mx';
while($line){
        $line =~m/\w+|{\w+\s+\w+}/; $line = $';
        print $&,"\n";
}

-----OUTPUT-----
Iteration
{Applied Field}
{Total Energy}
Mx

##</code><code>##

$line = 'Iteration {Applied Field}  {Total Energy}    Mx ';
print "$1\n" while $line=~s/(\w+\s+\w+|\w+)[}|\s+|\s+{]//;

Iteration
Applied Field
Total Energy
Mx

##</code><code>##

$line = 'Iteration {Applied Field} A  {Total Energy}    Mx  F G {Third test line}';
print "$&\n" while $line=~s/(?<={)[\w\s]+(?=})|\w+//;

Iteration
Applied Field
A
Total Energy
Mx
F
G
Third test line