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The properties of ternary mixed magnetic Co 1− x Mn y Ni x − y Cl 2 ·2H 2 O are examined by dc magnetization and susceptibility measurements, from 1.8 to 300 K as a function of composition. This is only the second ternary magnetic insulator so studied. The three transition metal chloride dihydrate components are known to differ in the degree of spin anisotropy and in the distribution of ferromagnetic and antiferromagnetic exchange interactions within and between strongly coupled chemical and structural chains. The Curie and Weiss constants, in χ M = C /( T − θ ) fits to high temperature susceptibilities, are compared with weighted averages of pure component values. The observed Weiss constant is almost uniformly less negative than calculated. Maxima in low temperature susceptibilities vary widely in presence and location with composition. Some compositions exhibit no susceptibility maximum, many exhibit one maximum, and three exhibit two maxima. A T ( x , y ) diagram is constructed. Magnetization vs field isotherms exhibit different shapes as a function of composition, with hysteresis markedly composition dependent. For three mixtures hysteresis loops are studied as a function of temperature. An activation process model does not describe the temperature dependence well. [ABSTRACT FROM AUTHOR]

Abstract: The magnetic properties of Mn1− x Ni x Cl2·2H2O are examined by DC magnetization and susceptibility measurements on a wide range of compositions. The pure components are three-dimensional Heisenberg antiferromagnets, ordering at 6.7K (MnCl2·2H2O) and at 7.25 K (NiCl2·2H2O). Each contains MC12MC12M… chemical (and structural) chains, with intrachain exchange ferromagnetic and antiferromagnetic in the Ni and Mn materials, respectively. Interchain exchange is predominantly antiferromagnetic in each. The Curie and Weiss constants, in fits to high temperature data, vary regularly with composition. C(x) is essentially linear, and exhibits systematic curvature which is analyzed to show that unlike-ion exchange is antiferromagnetic and weaker than like-ion interactions. The form of the susceptibility evolves with composition: maxima in ) broaden and shift to lower temperature with admixture of either component, but beyond about 20% minority component such maxima are absent, with upturns appearing instead. T c descends rapidly with admixture from either composition extreme, but varies only weakly between and 0.70. Magnetization isotherms display a subtle composition dependence which suggests that the ordered state differs for intermediate compositions from those for the composition extremes. Although frustration in mixtures is likely, from competing (sign) intrachain interactions, it is not strong enough to yield magnetic irreversibilities or time dependences signaling a spin glass phase. [Copyright &y& Elsevier]

Heat capacity measurements from 0.6 to 40 K are reported for various compositions of mixed magnetic Co1−xMnxCl2·H2O. For x=0.40–0.80 only broad maxima in the heat capacity appear. For x=0.90 a sharp peak is seen, at 1.727±0.005 K, but is not ideally lambda-like, due to effects of disorder. A lattice separation is made using results from earlier analyses of the heat capacities of the pure components. The resulting C(mag) displays a better resolved but still very broad maximum, for which the size increases with increasing x while the location, Tmax, decreases. Approximately 90% of the theoretical entropy in various mixtures accumulates up to 40 K. For the x=0.40 and 0.50 mixtures significantly less than half the theoretical entropy accumulates up to Tmax. For these two compositions a linear regime in the low temperature heat capacity is apparent, below 2.4 and 2.1 K for x=0.40 and 0.50, respectively, which are taken as spin glass transition temperatures Tg. Very similar characteristic temperatures were found for the irreversible magnetization behavior in earlier work on the same mixed system. The present results show that the combined effects of disorder and frustration suppress magnetic ordering over a remarkably broad composition range in Co1−xMnxCl2·H2O. [Copyright &y& Elsevier]