Study On The Magnetic Entropy Change And Magnetic Phase Transition Of Nazn13-Type Lafe13-Xalxcy Compounds

The refrigerant capacity and magnetic phase transition of NaZn13-type LaFe13-x. Al-x C-0.1., ( x = 1.6, 1. 8) interstitial compounds are investigated. The magnetic entropy change vertical bar Delta S vertical bar(m), which is calculated from one of the Maxwell's relationships Delta S(T, H) = - integral(partial derivative M/partial derivative T)(H)dH, is lower than that of carbides with low Al content. Although the magnetic entropy change peak broadens with increasing Al content, the value of q, which is used to evaluate the refrigerant capacity, decreases due to the sharp derease of the magnetic entropy change. Taking the spin fluctuation into account, the magnetic free energy can be expanded up to the M-6 term based on the Landau phase transition theory. The order of phase transition is distinguished by the the signs of a(3) (T) which is the coefficient of M-4 term. The order of phase transition for LaFe13 Al. carbides changes from the first one that is weak to the second one with the increase of Al content.