Isofield low-temperature specific heat of single-crystal Ho1-xYxNi2B2C (x=0,0.25,0.5,1):: Probing the magnetocaloric effect in HoNi2B2C -: art. no. 014429

Isofield specific heat, C(T,H), of single-crystal Ho1-xYxNi2B2C (x=0, 0.25, 0.5, 1) were measured within the ranges 0.5 K<T<50 K and H(parallel toa)less than or equal to60 kOe. Linearized spin-wave theory is invoked to analyze the field and temperature dependence of the magnetic specific heat and entropy of HoNi2B2C for T<T-N,H<H-1 and T<T-N, H>H-3. Based on the known low-temperature H-T phase diagram of HoNi2B2C, this analysis identifies three distinct field regions. (i) The low-field region (H<H-1) where the collinear, commensurate NE arrowSW arrow structure is stabilized, and C-M(T<T-N,H) and S-M(T<T-N,H) are well described by the prediction of linearized antiferromagnetic spin-wave analysis. In particular, (partial derivativeS(M)/partial derivativeH)(T)>0, indicating that cooling can be effected by adiabatic magnetization. (ii) The intermediate-field region (H-1<H<H-3), where the two metamagnetic states (namely NE arrowNE arrowSW arrow at H-1 and NE arrowNE arrowNW arrow at H-2) are stabilized. Here no spin-wave analysis is attempted, but it is evident that (partial derivativeS(M)/partial derivativeH)(T)>0 for H<H-2 while (partial derivativeS(M)/partial derivativeH)(T)<0 for H>H-2. (iii) The high-field region (H>H-3) where the saturated NE arrowNE arrow state is being approached. Here, both C-M(T<T-N,H) and S-M(T<T-N,H) follow the description of a ferromagnetic spin-wave analysis; furthermore, (partial derivativeS/partial derivativeH)(T)<0, indicating that cooling can be effected by adiabatic demagnetization. The magnetocaloric effect above T-N as well as alloying influences on the magnetic properties are discussed.