S. I. Reiman

Local spin configurations of Fe atoms in the Rh1−xFex (x=0.1, 0.2, and 0.3) system with competing exchange interactions

The local spin configurations of Fe atoms in the magnetically ordered alloys Rh1−xFex (x=0.1, 0.2, and 0.3) have been investigated by Mössbauer spectroscopy. The Mössbauer absorption spectra are measured in the range from 5 K to temperatures of the transition to the paramagnetic state. The measurements in magnetic fields with a strength up to 5 T are carried out at a temperature of 4.2 K. Analysis of the magnetic-hyperfinefield distribution functions demonstrates that Fe atoms form discrete sets of collinear spin configurations corresponding to different net moments of the nearest coordination sphere. The spin structure of the alloys is governed by a random distribution of Fe atoms over the lattice sites and the competition between the Fe-Rh ferromagnetic exchange interaction and the antiferromagnetic interaction of the neighboring Fe atoms. No spin frustration and spin “melting” effects characteristic of spin glasses are revealed in the Rh-Fe alloys.

Thermal destruction of antiferromagnetic Fe-Fe exchange bonds and mechanism of the transition to the spin-glass state in (Fe0.65Ni0.35)1−xMnx systems with antiferromagnetic competing exchange interactions

The thermal evolution of the competition between the ferro-and antiferromagnetic exchange interactions in (Fe0.65Ni0.35)1−xMnx alloys, which display different magnetic properties, depending on composition and temperature, is investigated. The distribution functions of the magnetic hyperfine fields P(Bhf) for 57Fe are determined by Mössbauer 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 Is(T) is analyzed for the low-and high-field portions of P(Bhf). The features found in the behavior of Is(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 exchange bonds and the magnetic transitions of the Fe-Ni-Mn system to the spin-glass state is considered.

Temperature evolution of frustrated spin states in the system with competing exchange interactions. Fe0.65Ni0.35)1−xMnx (x=0, 0.024, 0.034)

The influence of temperature on the distribution function P(Bhf) of the magnetic hyperfine fields for 57Fe in (Fe0.65Ni0.35)1−xMnx alloys (x=0, 0.024, 0.034) are investigated by Mössbauer spectroscopy. The Mössbauer absorption spectra are measured in the temperature interval 5–300 K; in the interval 5–80 K the measurements are performed in a magnetic field of 0.2 T. Anomalies are found in the temperature curves of the intensity of the principal maximum of the functions P(Bhf)[Bhf=30–38 T] and the total (integrated) intensities of the low-field components [Bhf=(4–13) T]. The detected anomalies in the behavior of the total intensities are interpreted as resulting from a change in the balance of competing exchange interactions due to the thermal annihilation of antiferromagnetic Fe-Fe exchange interaction. The emergence of strong satellite lines in the interval Bhf=20–29 T in Mn-doped alloys is attributed to reorientation of the spins of Fe atoms under the influence of strong antiferromagnetic Mn-Fe exchange interaction.