If you change the scale of axes and plot the data afterwards, the scale will get modified according to the data. Better to change the scale after plotting.
Note the warnings.
load('data5a_chi1-15.mat')
freq_sam = 100; % samples
period_ctrw = 0.005; % time period
freq_ctrw = 1/period_ctrw; % frequency
data_ctrw = data.variable.turbulence(:,100);
x_data = data.variable.turbulence(:,1);
y_data = data.variable.turbulence(:,100);
%disp(x_data);
%disp(y_data);
signal_ctrw = data_ctrw;
fft_ctrw = fft(signal_ctrw); % fourier transform
fft_ctrw = fftshift(fft_ctrw); % performing fft shift
f = freq_sam/2*linspace(-1,1,freq_sam);
figure;
plot(f, fft_ctrw,'.','MarkerSize',24);
set(gca, 'XScale', 'log')
set(gca, 'YScale', 'log')
