How do I store a figure inside a variable?

I have my program creating and storing the figure data inside a variable however unlike other variables, when the program ends the values inside the created variable are cleared. If you reach the end by stepping through however, the values remain.

    n.engine.powerCurveFig = figure;

    title('Engine Power and Torque vs RPM');
    xlabel('Engine Speed [RPM]');
    xlim([n.engine.aRPM(1,1) n.engine.aRPM(n.engine.numStates,1)]); 
    set(gca,'xtick', (n.engine.aRPM(1,1):500:n.engine.aRPM(n.engine.numStates,1)));
    grid on

    yyaxis right
    plot(n.engine.aRPM,n.engine.aTorque);
    ylabel('Engine Torque [ft*lb]');
    figure(n.engine.powerCurveFig);
    yyaxis left
    plot(n.engine.aRPM,n.engine.aPower);
    ylabel('Engine Power [HP]');

[Stephen23]

You should be using graphics handles:

https://www.mathworks.com/help/matlab/learn_matlab/understanding-handle-graphics-objects.html