Low-Temperature Magnetic Properties of Dilute Mg-Mn, Al-Mn, Mg-Fe, and Al-Fe Alloys

Abstract

Magnetic susceptibility measurements are reported on some dilute alloys of Mg-Mn and Al-Mn in the temperature range, room temperature -1.3\ifmmode^\circ\else\textdegree\fi{}K. Electron spin resonance (ESR) absorption has been observed in the magnesium alloy containing 0.6 at.% manganese and studied as a function of temperature. Room temperature magnetic susceptibility measurements and low temperature ESR experiments are reported for Mg-Fe and Al-Fe alloys. The concentration dependence of the Curie constant at high temperature suggests the presence of four unpaired electrons for the manganese atom dissolved in magnesium. Similar information concerning manganese dissolved in aluminum suggests one unpaired electron if a completely localized $d$ state is formed.The susceptibility of dilute Mg-Mn alloys shows departures from a Curie law, which could be interpreted as an increase in the spin state of the manganese ion in the region of the resistance minimum. This excess paramagnetism is discussed in terms of the possible mechanisms which could produce a resistance minimum and leads to the conclusion that if there is a ferromagnetic coupling between randomly distributed manganese pairs, the interaction mechanism operates over approximately 10 lattice spacings.The effective magneton number of Mn in the more dilute Mg-Mn alloys also increases with temperature at high temperatures. The susceptibility of the concentrated Mg-Mn alloy obeys a Curie law except in the region of the resistance maximum where both susceptibility and ESR data indicate an antiferromagnetic transition.The influence of the low-temperature transition, occurring in the magnesium alloy containing about 0.6 at.% manganese, on the electron spin resonance linewidth and magnetic field value has been measured as a function of temperature giving $g$ values of 2.01\ifmmode\pm\else\textpm\fi{}0.01 above 6\ifmmode^\circ\else\textdegree\fi{}K. The shift of the position of resonance field below 6\ifmmode^\circ\else\textdegree\fi{}K is consistent with antiferromagnetic behavior in Mg-Mn. The line shift is proportional to ${T}^{\ensuremath{-}1}$ in the antiferromagnetic region which would be consistent with a conduction electron superexchange mechanism for the antiferromagnetic manganese ion interaction. The linewidth is broadened in the region of the resistance minimum and attains a constant value as the temperature is lowered. This behavior is consistent with localized spin interactions, giving rise to larger averaged spin values in the resistance minimum region as suggested from the magnetic susceptibility studies of the more dilute alloys.