The change in the character of phase transition with nickel in the Ho(Co,Ni)2 compounds |
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Authors: | A Tari |
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Institution: | Department of Physics, Univ. of Petroleum & Minerals, Dhahran, Saudi Arabia |
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Abstract: | The series Ho(Co1-cNc)2 has been investigated in the composition range c?0.15 by spin-echo NMR of 165Ho and by magnetic measurements. From NMR data a value of (9.5±0.1)μB is estimated for holmium in HoCo2. Magnetisation measurements on the same compound give (7.9±0.1)μB/fu. An assumption of 0.8μB for the cobalt moment aligned antiparallel to that of holmium leads to a value of 9.5μB for holmium in agreement with the value estimated from NMR. The substitution of nickel for cobalt causes a rapid fall in both the hyperfine field, and the ordering temperatures, while the molecular moment shows a simultaneous rise. These are attributed to a rapid fall in the cobalt moment which leads to a bootstrap process involving the strength of the exchange field and the magnitude of the cobalt moment. Nickel substitution also leads to a change in the character of the magnetic phase transition. Initially first order, this transition becomes second order on exceeding ≈ 9 at% Ni. |
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