Magnetic and magnetocaloric properties and the magnetic phase diagram of single-crystal dysprosium

Abstract

Magnetic materials exhibiting magnetic phase transitions simultaneously with structural rearrangements of their crystalline lattices hold promise for numerous practical applications including magnetic refrigeration, magnetomechanical devices, and sensors. We undertook a detailed study of a single crystal of dysprosium metal, which is a classical example of a system where magnetic and crystallographic sublattices can be either coupled or decoupled from one another. Magnetocaloric effect, magnetization, ac magnetic susceptibility, and heat capacity of high-purity single crystals of dysprosium have been investigated over broad temperature and magnetic field intervals with the magnetic field vector parallel to either the a or c axes of the crystal. Notable differences in the behavior of the physical properties when compared to Dy samples studied in the past have been observed between 110 and 125 K, and between 178 and ϳ210 K. A plausible mechanism based on the formation of antiferromagnetic clusters in the impure Dy has been suggested in order to explain the reduction of the magnetocaloric effect in the vicinity of the Néel point of relatively impure samples. Experimental and theoretical investigations of the influence of commensurability effects on the magnetic phase diagram and the value of the magnetocaloric effect have been conducted. The presence of newly found anomalies in the physical properties has been considered as evidence of previously unreported states of Dy. The refined magnetic phase diagram of dysprosium with the magnetic field vector parallel to the a axis of a crystal has been constructed and discussed.FIG. 26. ͑Color online͒ The temperature dependencies of the magnetocaloric effect of Dy as calculated from the heat capacity data.

Magnetic and thermal properties of Er75Dy25single crystals

“…Three transitions are observed: at ∼ 30 K, ∼ 45 K, and ∼ 110 K. The sharp peak at T C ≅ 30 K corresponds to the first order AFM-FM transition. A similar transition (sharp peak) is observed in the C P data of pure Er at T C ≅ 19 K. 33,34 In pure Dy, the first order C P peak is observed at T C ≅ 90 K. 3,7 The transition observed at ∼45 K resembles the anomaly observed in the C P of pure Er at T N ⊥ ≅ 53 K, where the CAM structure transforms into the APD magnetic structure. 3,33 No such anomaly is observed in pure Dy.…”

“…The AFM order changes over to the FM one below T C ≅ 90 K. When a magnetic field is applied anywhere between T C and 135 K, the magnetic structure of Dy changes from a helix AFM to FM. 7,17 Between 135 K and 180 K, the AFM-FM transition is separated by an intermediate fan magnetic phase, which is stable between ∼7 and ∼25 kOe. 7,17 Low temperature x-ray diffraction studies of single crystal Dy showed that the FM transition at 90 K is accompanied by a structural transition from hcp to a distorted orthorhombic structure along with significant discontinuities in lattice parameters.…”

“…7,17 Between 135 K and 180 K, the AFM-FM transition is separated by an intermediate fan magnetic phase, which is stable between ∼7 and ∼25 kOe. 7,17 Low temperature x-ray diffraction studies of single crystal Dy showed that the FM transition at 90 K is accompanied by a structural transition from hcp to a distorted orthorhombic structure along with significant discontinuities in lattice parameters. 18,19,20 Below T N , only a strong expansion of the c parameter is reported.…”

“…6 Elemental Dy, which is paramagnetic at room temperature, also exhibits several magnetic field and temperature driven magnetic transitions. 7,14,15,16 Upon cooling down to the Neel 3 temperature, T N ≅ 180 K, in zero magnetic field, the PM Dy transforms into a helix AFM ordered state. The AFM order changes over to the FM one below T C ≅ 90 K. When a magnetic field is applied anywhere between T C and 135 K, the magnetic structure of Dy changes from a helix AFM to FM.…”

“…1,2,3,4,5,6,7 Both metals adopt hexagonal closed packed (hcp) crystal structure at room temperature, 6,8,9 and upon cooling down from room temperature, they both undergo a series of phase transitions where either or both magnetic and crystallographic sublattices are affected. 8 Earlier investigations of Er performed using neutron and x-ray diffraction 1,10,11 show that an antiferromagnetic (AFM) transition occurs at T N || ≅ 84 K (magnetization is parallel to the c axis), where paramagnetic (PM) compound orders in a c axis modulated (CAM) structure.…”