26 Journal of Magnetism and Magnetic Materials 96 (1991) 26-28 North-Holland Magnetic part of specific heat in high-purity Dy single crystal S.A. N&tin, A.M. Tishin, S.F. Savchenkova, Yu.1. Spichkin, O.D. Chistykov, S.V. Red’ko and Yu.A. Nesterov lleparrmen~ of Physics, Moscow State University, 119899 Moscow, USSR Received 24 September 1990; in revised form 24 October 1990 The specific heat and spontaneous magnetization of high-purity Dy single crystal are measured in the temperature range 4.2-300 K. The magnetic contribution to the specific heat is determined and the magnetic part of the entropy is calculated. The magnetic ordering in the paramagnetic region above the Neel temperature is discussed. 1. Introduction The magnetic and elastic properties of Dy single crystal have been studied in ref. [l] and the tem- perature hysteresis of elasticity modulus E and dynamic susceptibility x have been observed in the paramagnetic region above the NCel tempera- ture 0,=179 K up to r,=290 K (at T=T, hysteresis vanishes). The maximum of internal friction Q -i at T, has also been observed. Earlier, in ref. [2], the hysteresis of intensity of magnetic reflex, the angle of helicoid and the factor of neutron depolarization have been studied using the neutron diffraction method. This hysteresis was still present tens of degrees Celsius above O2 (0, - the point of phase transition from antiferro- magnetic to paramagnetic state). The authors of ref. [3] pointed out that the magnetic part of the entropy of Dy increased for temperatures well above 0,. In ref. [4] the magnetic contribution of specific heat of Dy was found above 0,. Observed phenomena can be explained by the existence in the paramagnetic region of short-range magnetic ordering as clusters of ordered spins which con- centration is different under heating and cooling. The authors of the theoretical work [5] have shown that in the paramagnetic region the “local phase transformation” with reconstruction of short-range ordering may exist. Obviously this transformation may cause the peak on the Q-’ temperature de- pendence at TH, In connection with many papers about short- range magnetic ordering in the paramagnetic re- gion [l-4] the investigation of the properties of transformation of magnetic ordering of high-pur- ity Dy single crystal is important. In such a crystal the effects caused by impurity and crystal imper- fections are negligible. In the present paper the specific heat cP and spontaneous magnetization us of Dy single crystal are measured. The obtained results allow us to study the experimental temper- ature dependence of the magnetic part of specific heat (c,,,,) and compare it with values calculated from molecular-field theory [6]. The parameter cM is sensitive to transformation of magnetic struc- ture and its disordering. 2. Experimental details We use samples of Dy single crystal with a ratio of specific resistance at 4.2 and 300 K of p3,,0/p4.2 = 200. The samples are refined by vacuum sublimation in a resistance furnace with a graphite heater under a residual pressure of 10P6 Torr. The refined metal is deposited on the watercooled copper condenser forming druses with orientation along one of three crystallographic directions 0304-8853/91/$03.50 0 1991 - Elsevier Science Publishers B.V. (North-Holland)