Thermal destruction of antiferromagnetic Fe-Fe exchange bonds and mechanism of the transition to the spin-glass state in (Fe_(0.65)Ni_(0.35)_(1-x)Mn_x systems with antiferromagnetic competing exchange interactions

摘要

The thermal evolution of the competition between the ferro- and antiferromagnetic exchange interactions in (Fe_(0.65)Ni_(0.35)_(1-x)Mn_x alloys, which display different magnetic properties, depending on composition and temperature, is investigated. The distribution functions of the magnetic hyperfine fields P(B_(hf)) for ~(57)Fe are determined by Mossbauer spectroscopy in the temperature range 5-300 K for the alloys with x = 0, 0.024, 0.082, 0.136, 0.195, and 0.252. The temperature dependence of the integrated intensity I_s(T) is analyzed for the low- and high-field portions of P(B_(hf)). The features found in the behavior of I_s(T) are interpreted as results of variation of the ratio between the competing exchange interactions of different signs as a result of the thermal destruction of antiferromagnetic Fe-Fe exchange bonds. It is shown that the changes in the spin structure in the low-temperature range are due to the thermal destruction of Fe-Fe exchange bonds. One of the consequences of this destruction is "reentrance" (an increase in the hyperfine field with increasing temperature for some of the Fe atoms). The relationship between the thermal destruction of Fe-Fe exchanges bonds and the magnetic transitions of the Fe-Ni-Mn system to the spin-glass state is considered.