In superconducting ferromagnets for which the Curie temperature T m exceeds the superconducting transition temperature T c , it was suggested that ferromagnetic spin fluctuations could lead to superconductivity with p-wave spin-triplet Cooper pairing. Using the Stoner model of itinerant ferromagnetism, we study the feedback effect of the p-wave superconductivity on the ferromagnetism. Below T c , the ferromagnetism is enhanced by the p-wave superconductivity. At zero temperature, the critical exchange interaction value for itinerant ferromagnetism is reduced by the strength of the p-wave pairing potential, and the magnetization increases correspondingly. More important, our results suggest that once the ferromagnetism is established, T m is unlikely to ever be below T c . For strong and weak ferromagnetism, three and two peaks in the temperature dependence of the specific heat are, respectively, predicted, the upper peak in the latter case corresponding to a first-order transition.

It has been suggested that either the diamagnetism or paramagnetism of Bose gases, due to the charge or spin degrees of freedom respectively, appears solely to be extraordinarily strong. We investigate the magnetic properties of charged spin-1 Bose gases in an external magnetic field, focusing on the competition between the diamagnetism and paramagnetism, using the Lande-factor g of particles to evaluate the strength of the paramagnetic effect. We propose that a gas with g < 1/√8 exhibits diamagnetism at all temperatures, while a gas with g > 1/2 always exhibits paramagnetism. Moreover, a gas with the Lande-factor in between shows a shift from paramagnetism to diamagnetism as the temperature decreases. The paramagnetic and diamagnetic contributions to the total magnetization density are also calculated in order to demonstrate some details of the competition.

The magnetic properties of a charged spin-1 Bose gas with ferromagnetic interactions are investigated within mean-field theory. It is shown that a competition between paramagnetism, diamagnetism and ferromagnetism exists in this system. It is shown that diamagnetism, being concerned with spontaneous magnetization, cannot exceed ferromagnetism in a very weak magnetic field. The critical value of reduced ferromagnetic coupling of the paramagnetic phase to ferromagnetic phase transition I[combining overline](c) increases with increasing temperature. The Landé-factor g is introduced to describe the strength of the paramagnetic effect which comes from the spin degree of freedom. The magnetization density M[combining overline] increases monotonically with g for fixed reduced ferromagnetic coupling I[combining overline] as I[combining overline] > I[combining overline](c). In a weak magnetic field, ferromagnetism makes an immense contribution to the magnetization density. On the other hand, at a high magnetic field, the diamagnetism tends to saturate. Evidence for condensation can be seen in the magnetization density at a weak magnetic field.

The charged Fermi gas with a small Lande-factor g is expected to be diamagnetic, while that with a larger g could be paramagnetic. We calculate the critical value of the g-factor which separates the dia-and para-magnetic regions. In the weak-field limit, gc has the same value both at high and low temperatures, gc = 1/ √ 12. Nevertheless, gc increases with the temperature reducing in finite magnetic fields. We also compare the gc value of Fermi gases with those of Boltzmann and Bose gases, supposing the particle has three Zeeman levels σ = ±1, 0, and find that gc of Bose and Fermi gases is larger and smaller than that of Boltzmann gases, respectively.

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