Magnetic behavior and structural data of the U(T x Al 1-x)2 compounds, where T = Co, Ni and Mn , were reported. Magnetic measurements were performed in the temperature range 4.2–800 K and magnetic fields up to 7 T. The gradual replacement of Al by Co , Ni and Mn ions leads to the decrease of the effective magnetic moments per uranium ion, and of the paramagnetic Curie temperatures in absolute magnitude. This composition evolution of the two magnetic parameters of the U(T x Al 1-x)2 compounds suggests a gradual suppression of the spin fluctuations with replacing the Al ions by T ions.

The magnetic properties of the U 1-x Y x NiAl system were studied in the 4–600 K temperature range fields up to 7 T. The systems with x≤0.8 were analyzed in terms of the spin fluctuations theory. The system presents a Curie–Weiss type behavior over a certain temperature T*. The paramagnetic Curie temperatures are negative and decrease in absolute magnitude as yttrium content increases. The effective magnetic moment per uranium atom is composition independent (≈3.1 μB) proving the presence of temperature induced spin fluctuations.

The magnetic and structural study of UxGd1-xAl4 system was performed. The magnetic properties investigated in the 4-600 K temperature range and fields up to 90 We showed the magnetic order for x less than or equal to 0.8. The different magnetic behaviour types were evidenced from ferromagnetic (x = 0) to mictomagnetic and spin glass (0.2 less than or equal to x less than or equal to 0.8) and to spin fluctuations (x = 1). The change in the magnetic properties is correlated with the substitutional disorder that occurs in the Gd clusters having easy axes randomly aligned superposed on the spin fluctuations due to uranium atoms. (C) 2003 WILEY-VCH Vertag GmbH & Co. KGaA, Weinheim.

The magnetic properties of the U1−xDyxSi2−δ systems were studied in the 4 to 600 K temperature range and fields up to 8 T. The magnetic behaviour of USi2−δ was discussed in terms of the spin fluctuations model. The systems having x≤0.8 show a similar behaviour. The paramagnetic Curie temperatures are negative and the effective magnetic moments per uranium atom are almost linearly decreasing from 3.57 μB as x increases. This behaviour is attributed to a gradual quenching of the spin fluctuations determined by the local internal field due to the Dy atoms.

The magnetic properties of the U1−xLaxAl4 system were investigated in the 4–600 K temperature range and fields up to 7 T. The UAl4 compound shows a magnetic behaviour typical for a spin fluctuations system. The U1−xLaxAl4 systems present Curie–Weiss type behaviour for x≤0.6 and above a certain temperature T*. The negative paramagnetic Curie temperatures and the effective magnetic moment values indicate the presence of spin fluctuations. For x≥0.8 a temperature-independent susceptibility is observed. As the lanthanum content increases from x=0 to 0.6 the effective magnetic moment per uranium atom remains constant.

The magnetic properties of the U1−xGdxLaAl4 system were investigated in the 4–600 K temperature range and fields up to 8 T. The ULaAl4 compound shows magnetic behaviour typical for a spin fluctuations system. When uranium is replaced by gadolinium magnetic ordering is evidenced. In the paramagnetic region the susceptibilities follow a Curie-Weiss type behaviour. For increasing gadolinium content a decrease of the effective uranium magnetic moments was observed. This behaviour was attributed to a gradual quenching of spin fluctuations by the internal field.

The magnetic properties of (U1-xDyx)Ni-5 compounds were studied in the temperature range 2-800 K and fields up to 7 T. The compounds having x greater than or equal to 0.2 are magnetically ordered. Above the Curie points, the reciprocal susceptibilities follow a modified Curie-Weiss behaviour. UNi5 is a paramagnet. A peak in the temperature dependence of the magnetic susceptibility is evidenced at T approximate to 20 K. For T > 140 K the UNi5 susceptibility is temperature independent.

Magnetic measurements were performed on U1−xRxAl3 compounds with R = Gd and Dy in the temperature range 400–600 K and fields up to 7 T. UAl3 shows a spin fluctuation-type behaviour. The effective uranium moment, determined in the high temperature range, is 3.62 μB. When replacing U by Gd or Dy, at low temperatures the susceptibilities follow a Curie-Weiss-type behaviour. The effective uranium moments decrease when the rare earth content is increasing. This behaviour is attributed to gradual quenching of spin fluctuations.

Magnetic measurements were performed on U(1-x)R(x)Al(3) with R = La or Y in the temperature range 4(77)-700 K and fields up to 7 T. UAl3 is a spin fluctuation system. When uranium is substituted by Y or La the effective magnetic moments decrease together with the absolute magnitude of theta. This suggests a gradual quenching of the spin fluctuations with increasing R content.

The magnetic properties of the U(Al1−xCox)4 system were studied in the temperature range 2 to 800 K and fields up to 7 T. UA14 shows a spin fluctuations-type behaviour. A gradual quenching of spin fluctuations is evidenced when aluminum is replaced by cobalt.

The magnetic properties of the U(CoxAl1−x)3 system were studied in the temperature range 4.2 and 700 K and fields up to 70 kOe. UAl3 shows a spin fluctuations-type behaviour. A gradual quenching of spin fluctuations is evidenced when aluminium is replaced by cobalt.

The magnetic properties of xUCo5.3(1−x)UNi5 compounds were studied in the temperature range 2–800 K and fields up to 70 kOe. UNi5 is a paramagnet. A peak in the temperature dependence of the magnetic susceptibility is observed at T≈20 K. The compounds with x⩾0.2 are ferromagnetically ordered. The mean cobalt moments decrease from about 0.32 μB for x = 1.0 to about 0.15 μB for x = 0.2. Above the Curie temperatures the reciprocal susceptibilities show a Curie-Weiss-type behaviour. The effective cobalt moments are close to those of Co2+ ions. The experimental data are analysed in terms of the spin fluctuation model.

The result of magnetic measurements performed on UxGd1−xAl2 and UxDy1−xAl2 compounds are reported. The effective moments per uranium decrease nearly linearly when increasing the Gd or Dy content, suggesting a gradual quenching of spin fluctuations.

The results of magnetic measurements performed on U(Ni x Al 1− x ) 2 alloys in the temperature range 4.2 and 800 K are reported. By gradual replacement of aluminum by nickel up to x < 0.8, the effective uranium moments as well as the paramagnetic Curie temperature decrease. These suggest a gradual suppression of spin fluctuations. UNi 2 is a weak itinerant ferromagnet. In this compound the spontaneous magnetization follows a T 2 dependence.

The results of magnetic measurements performed on U x La 1− x Al 2 and U x Y 1− x Al 2 compounds are reported. Above ∼ 60 K, the temperature dependences of susceptibilities were analysed assuming a superposition of a temperature dependent term on a Pauli-type contribution. The paramagnetic Curie temperature, θ, decrease in absolute magnitude by increasing La or Y content. The effective moments per U atom vary from 3.06 μ B for x = 1.0 up to 2.60 μ B for x = 0.2. The experimental data were analysed in correlation with the separation between the uranium ions.

The results of magnetic measurements performed on U(Mn x Al 1−x ) 2 compounds in the temperature range 4.2K < T < 800K are reported. In the low temperature range ( T < 200K), UMn 2 shows a Pauli-type paramagnetism. Above 420K a Curie-Weiss behaviour is evidenced. The magnetic properties of U(Mn x Al 1−x ) 2 compounds were analysed assuming a superposition of a temperature dependent term on a Pauli-type contribution, χ O . The effective moments as well as the χ O values were determined both in the low ( T < 200K) and high ( T > 420K) temperature range. The experimental data were discussed considering changes in the band structure and/or quenching of spin fluctuations.