Magnetocaloric Effect Study on the Pyrochlore Spin Ice Compound Dy₂Ti₂O₇ in a [111] Magnetic Field

Abstract

Field variation of the entropy S(H) of the spin ice compound Dy₂Ti₂O₇ has been examined by means of magnetocaloric effect measurements in a magnetic field H||[111], with attention focused on the ice-rule breaking spin-flip transition. At T=0.35 K, S(H) exhibits a plateau in the kagomé ice state up to ∼0.8 T, followed by a sharp decrease at 0.9 T where a first-order transition to the saturated state occurs. Slightly above the critical point of the transition (T_cr\\simeq0.36 K), S(H) at 0.4 K and 0.5 K exhibits a pronounced peak at the spin flip field of ∼0.9 T indicating an enhanced degeneracy due to coexistence of “two-in, two-out” and “three-in, one-out” states at the field. The peak height of S(H) is, however, strongly temperature dependent and substantially smaller than that expected from a nearest-neighbor spin ice model, suggesting the presence of certain magnetic correlation in the system.