Temperature dependence of nuclear spin-relaxation rates for Fe, Co and Ni

Abstract

Numerical calculations of the temperature dependence of the longitudinal (T1-1) and transverse (T2-1) nuclear spin-relaxation rates for Fe, Co and Ni are performed for both ferromagnetic and paramagnetic states, using the first-principles density of states and various approximations of the spin-fluctuation theory. If the spin fluctuations are taken into account, the quantities (T1T)-1 and (T2T)-1 depend significantly on temperature. Near TC in the ferromagnetic region they increase sharply, the increases being monotonic and similar for the two rates, just as observed experimentally.

Magnetic properties of Fe–Ni invar calculated in the dynamic non-local approximation of the spin fluctuation theory

“…It is easily proved that, in this case, one obtains the same equations as in the case of a single energy band with the only difference that the temperature T is replaced by T /N. The details of the calculations of the magnetic properties by the DNA of the SFT have been described in our papers [26,27,31].…”

“…In the present paper, for the first time we use the dynamic non-local approximation (DNA) of the SFT, developed in [25] and successfully applied to Fe, Co and Ni in [26][27][28], for investigation of the temperature dependence of the magnetic properties of Fe-Ni invar. Our approach is based on a self-consistent quadratic approximation for the free energy of electrons in a random exchange field.…”

Problem of temperature dependence in the dynamic spin-fluctuation theory for strong ferromagnets

“…First, we demonstrate that the instability is not an artefact of the calculation method. To this end, we show that the coordinate bisection method used in [4][5][6][7][8][9][10] gives a good agreement with the multidimensional minimization over a wide range of temperatures. Second, through the calculation with the forward and backward changes of temperature, we demonstrate the hysteresis behaviour of the magnetic characteristics.…”

“…Magnetic properties of transition metals and alloys at finite temperatures are usually calculated in the framework of various approximations of the spin-fluctuation theory (SFT) (see, e.g., [1][2][3] and references therein). A number of such approximations were developed in [4,5] and fairly successfully applied first to ferromagnetic metals Fe, Co and Ni [6][7][8] and then to the Invar alloy Fe-Ni [9,10].…”

“…Calculations [4][5][6][7][8][9][10] showed that the solution to the system of equations of the SFT can be unstable at high temperatures, well below the Curie temperature, T C . It is especially pronounced in Fe and Fe-Ni Invar, where spin fluctuations increase sharply in this region.…”