Perhaps you want to split your data into different variables and not files and to save all of them in a single file. One good way will be to use struct fields, another will be to use cell array.
For struct fields something like this can do the job
for i = 1:length(originalData)
currVar = strcat('data_hz_', num2str(i)); %a meaningful variable name for you
splitData.(currVar) = selectedData(x1:x2); %you can use index also like splitData.(currVar)(i,k)
you can re-structure however you want your variables also.