Spin injection dependent metamagnetic transition

The idea of the spin injection from ferromagneic metal to paramagnetic metal was first proposed by Aronov [1]. In the spin injection process the charge current flow between the ferromagnetic and paramagnetic metals produces the non-equilibrium magnetization in the paramagnet. This magnetization is proportional to the induced chemical potentials difference of electrons with opposite spins [1] the spin accumulation. Non-equilibrium spin imbalance due to injection was observed by Johnson and Silsbee [2]. The theory of spin injection was developed in details in many works [3–7] and well studied experimentally, see for a review [8, 9]. However, the degree of electron spin polarization is relatively small at standard spin injection from ferromagnetic to paramagnetic metal [10, 11]. In order to increase the non-equilibrium polarization it is interesting to look for the possibility of spin-injection based magnetic transition in metamagnetic metals. Here we consider the metamagnetic transition of itinerant electrons induced by the spin injection mechanism. Let us briefly describe the properties of the metamagnet [12, 13]. When the energy splitting of electrons with opposite spins is smaller than the characteristic energy scale of itinerant electrons, then magnetic part of the free energy density can be expanded in powers of magnetization F (H,M) = aM + bM + cM −MH , where coefficients a, b, c are determined by the energy dependence of the density of states at the Fermi level, H is the external magnetic field and M is the magnetization. At b < 0 magnetic part of free energy F (H = 0,M) might have extremum at nonzero |M | as it is shown in Fig. 1, which schematically illustrates evolution of free energy with increasing magnetic field due to contribution of the term −MH . At small magnetic field the state with low magnetization has lower energy, while at magnetic field larger than so called metamagnetic field Hm the metamagnetic state acquires lower energy and system undergoes to state with higher magnetization. Metamagnetic state is induced by external magnetic field through the first order phase transition [12, 13]. Metamagnetic transition of itinerant electrons might appear [12, 13] in strongly enhanced Pauli paramagnets when the Fermi level is close to peak in electron density of FIG. 1: Free energy F (H,M) dependence on the magnetization M of the metamagnet shown schematically for different magnetic fields H2 > H1. The state with higher magnetization has lower energy at higher magnetic fields. Inset: Dependence of the magnetization on magnetic field.