The Heat Capacity of Gadolinium Sulfate Octahydrate Below 1° Absolute

Magnetic Transition and Large Magnetocaloric Effect Associated with Surface Spin Disorder in Co and CocoreAgshell Nanoparticles

“…Historically, magnetocaloric refrigeration was used to reach milli-Kelvin temperatures in paramagnetic salts by using adiabatic demagnetization. [1][2][3] The magnetocaloric refrigeration in bulk materials has been studied in manganites, intermetallic compounds, Gd, Gd 5 (Si 2 Ge 2 ), 2,4 etc. Recently, considerable efforts have been made toward their high-temperature applications.…”

“…2,4 Giant magnetocaloric effect (MCE) has been mostly observed in bulk materials, such as Gd 5 (Si 2 Ge 2 ), and is understood to be due to the magnetic field induced first-order structural transitions. 1 Although the observation of giant MCE is promising, most of the current bulk MCE materials rely on the entropy change associated with the paramagnetic-ferromagnetic transition at the Curie temperature. The MCE shows a maximum in the vicinity of the Curie temperature and drops off sharply on either side.…”

“…7 In addition, the large surface area in nanostructured materials has the potential to provide better heat exchange with the surrounding materials. 1 However, to prevent agglomeration of nanoparticles, MCE studies have been mainly focused on nanocomposites where nanoparticles such as Fe, Fe 3 O 4 have to be dispersed in a matrix in order to prevent the agglomeration associated with the surface energy minimization. To date, not too many studies of the MCE in nanocomposites have been reported.…”

Nicholas Kurti, C.B.E. 14 May 1908 — 24 November 1998

“…Small magnets were available for producing fields in the region between 1 and 2 T. Nicholas anticipated that Simon's priority would lie with the successful demonstration of the use of adiabatic demagnetization, but Simon was unwilling to compete with Giauque, one of the proposers of the method, and for his first few years in Oxford, working with Nicholas, confined his attention to experiments on the properties of paramagnetic salts. Giauque and MacDougall in Berkeley (Giauque & MacDougall 1933, and de Haas and Wiersma in Leiden (de Haas & Wiersma 1934), successfully produced magnetic cooling; the former workers, using a magnet that produced a field of 0.8 T, cooled a sample of gadolinium sulphate from 2 K to a final temperature of 0.34 K, the latter, using potassium chrome alum and a field of 2.46 T, reached 0.05 K. During the next year Simon and Kurti at the Clarendon Laboratory, where a maximum field of 1.4 T was available, reached a temperature of 0.038 K in iron ammonium alum.…”

Temperatures below 1deg;

“…Space does not permit a detailed description of the many interesting features of tiiese developments, which, although started early in 1925, did not reach a sufficient state of completion to permit the use of adiabatic demagnetization in attain mg temperatures below 1°K. (7,9) until March 19, 1933. However, Figures 2 to 8 give some idea of the equipment used.…”