There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

The recent literature concerning the magnetocaloric effect (MCE) has been reviewed. The MCE properties have been compiled and correlations have been made comparing the behaviours of the different families of magnetic materials which exhibit large or unusual MCE values. These families include: the lanthanide (R) Laves phases (RM2, where M = Al, Co and Ni), Gd5(Si1−xGex)4 ,M n(As1−xSbx), MnFe(P1−xAsx), La(Fe13−xSix) and their hydrides and the manganites (R1−xMxMnO3, where R = lanthanide and M = Ca, Sr and Ba). The potential for use of these materials in magnetic refrigeration is discussed, including a comparison with Gd as a near room temperature active magnetic regenerator material. (Some figures in this article are in colour only in the electronic version)

https://iopscience.iop.org/article/10.1088/0034-4885/68/6/R04/pdf

Recent developments in magnetocaloric materials

In this chapter, we will restrict our attention to the ferrites and a few other closely related materials. The great interest in ferrites stems from their unique combination of a spontaneous magnetization and a high electrical resistivity. The observed magnetization results from the difference in the magnetizations of two non-equivalent sub-lattices of the magnetic ions in the crystal structure. Materials of this type should strictly be designated as “ferrimagnetic” and in some respects are more closely related to anti-ferromagnetic substances than they are to ferromagnetics in which the magnetization results from the parallel alignment of all the magnetic moments present. We shall not adhere to this special nomenclature except to emphasize effects, which are due to the existence of the sub-lattices.

Ferromagnetic materials

Surface plasmons (SPs) are coherent oscillations of conduction electrons on a metal surface excited by electromagnetic radiation at a metal -dielectric interface. The growing field of research on such light -metal interactions is known as ‘plasmonics’. 1-3 This branch of research has attracted much attention due to its potential applications in miniaturized optical devices, sensors, and photonic circuits as well as in medical diagnostics and therapeutics. 4-8

Nanostructured plasmonic sensors.

Review of the magnetocaloric effect in manganite materials

Formation of nanocrystalline Co particles embedded in an amorphous C matrix produced by the mechanical alloying process was studied The formation of the Co5C95 alloy was examined by the x-ray diffraction (XRD) and extended x-ray absorption fine structure methods XRD analysis displayed the decrease in the Co grains size, the transformation from the face-center-cubic (fcc)+hexagonal close-packed (hcp) phases to the hcp phase and an amorphization of carbon matrix with milling time At the early stage of milling, the coercivity, HC, increased because of the higher hcp phase HC than that of the fcc phase Partial HC increase could be also caused by the decrease of Co particles size The subsequent powder milling led to the decrease in the HC due to thermal process and/or due to the transformation of hcp-Co to a random close-packed phase under a long-term milling Magnetization of the compositions decreased gradually with milling The size of single domain particles after the 60 h of milling was about 10 nm 

Local structure and magnetic properties of mechanical alloyed Co-C compositions

Amorphous Sm-Fe thin films with excellent magnetostrictive properties are fabricated by rf magnetron sputtering and a magnetization behavior of the thin films is investigated by measuring the temperature dependence of magnetization with a SQUID and a VSM during heating from 5 to 600 K at an applied magnetic field of 10 or 50 kOe, and also measuring low temperature hysteresis loops. Magnetic parameters are discussed by using models based on the mean field theory and the random anisotropy. A particular emphasis is given to differing magnetic properties depending on fabrication method.

A magnetization behavior of giant magnetostrictive amorphous Sm-Fe thin films

The magnetocaloric effect and magnetization behavior have been analyzed in the double-perovskite Ba2FeMoO6 compound with the sintering temperature at 1273, 1373, and 1473 K. Samples were fabricated by conventional solid-state reaction method. X-ray diffraction measurements revealed that all the samples are single phase in cubic structure. Detailed investigations of the influence of sintering on magnetic entropy behavior of the sample exhibited the variation of TC. The magnetic entropy changes, ΔSM of about 0.98 ~ 1.93 J/kg K were obtained in the temperature range of 320-330 K for the Ba2FeMoO6 compound. The values of ΔSM are increased two times with increasing sintering temperature from 1273 to 1473 K. The enhancement of the magnetic entropy change is believed to be due to changes in the microstructure of the samples. It seems to favor the increase of magnetic order, which changes magnetic part of the entropy of a solid around the magnetic ordering temperature.

The Sintering Effect of Magnetic Entropy Change on ${\rm Ba}_{2}{\rm FeMoO}_{6}$

MnドープBaTiO 3 セラミックスの焼なまし温度が構造特性化と磁気的性質に及ぼす影響

We prepared Zn 1�x Mn x O nanorods by thermal diffusion. These samples were then studied the structural, optical, and magnetic properties. The structural analyses basing on x-ray diffraction and transmission electron microscope revealed the absence of Mn-related secondary phases. The study of photoluminescence spectra revealed the blueshift in the UV emission when the Mn doping concentration was increased, as a consequence of the extension of the band gap energy. Besides this situation, the increase in emission intensity associated with extrinsic defects at about 680 nm also took place. Concerning the Raman scattering spectra, apart from conventional phonon modes related to the ZnO wurtize-type structure, there were some additional modes introduced by the doping. Their origin was assessed carefully. Particularly, the shift in peak position of E2high toward low frequencies due to the increase in the Mn doping concentration could be explained well by means of the spatial correlation model. Magnetic measurements proved the samples with Mn concentrations above 1.15 at. % exhibiting the weak-ferromagnetic order at low temperatures. The nature of the ferromagnetism was discussed by means of the results of the structural and optical investigations. © 2010 American Institute of Physics. doi:10.1063/1.3478709

Seong-Cho Yu

Papers

Local structure and magnetic properties of mechanical alloyed Co-C compositions

A magnetization behavior of giant magnetostrictive amorphous Sm-Fe thin films

The Sintering Effect of Magnetic Entropy Change on ${\rm Ba}_{2}{\rm FeMoO}_{6}$

MnドープBaTiO 3 セラミックスの焼なまし温度が構造特性化と磁気的性質に及ぼす影響

Influence of Mn doping on structural, optical, and magnetic properties of Zn 1x Mn x O nanorods