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

Thermal treatment at high frequency giant magnetoimpedance in glass coated Co 83.2 B 3.3 Si 15.9 Mn 7.6 microwires

We have studied the magnetic properties of Nd45Fe30Co15Al10 alloy ribbons with various thicknesses of about 120 (N1) and 50 μm (N2) prepared by melt-spinning. Structural analyses based on an X-ray diffractometer and a high-resolution transmission electron microscope revealed an existence of nanocrystals with sizes of 10 ~ 20 nm surrounded by an amorphous host matrix. With decreasing ribbon thickness and nanocrystalline size, magnetic studies upon a vibrating sample magnetometer indicated the decrease of the Curie temperature (TC), coercive force (Hc), and magnetic entropy change (ΔSm). In the ferromagnetic region, however, magnetization values determined for N2 are greater than those determined for N1. These results are related to the differences in the critical exponents of N1 (β=0.418 and γ=1.173), and N2 (β=0.512 and γ=1.077), which are characteristic for the ferromagnetic nature existing in the alloy ribbons with different thicknesses.

Ferromagnetic Order in Rapidly Cooled Nd-Fe-Co-Al Alloy Ribbons

We present a detailed study on a large magnetocaloric effect at room temperature in polycrystalline ceramic samples of Pr1-xSrxMnO3 (x = 0.3, 0.4, and 0.45), exhibiting a second-order phase transition. The experimental results demonstrate the replacement of Sr2+ for Pr3+ in Pr1-xSrxMnO3, which leads to the Curie temperature (TC) increasing from 258 K for x = 0.3 to 301 K for x = 0.45. In particular, the maximum values of magnetic entropy change (|ΔSmax|) in the field H = 10 kOe are about 2.36-3.33 J·kg -1·K -1, corresponding to the refrigerant capacity RC = 50 - 53 J·kg -1 for x = 0.3-0.45. Based on the modified Arrott-plot method and the isothermal magnetization data around TC, we obtained the values of the critical exponents (β, γ, and δ) and TC for all the samples. Here, the values β = 0.370-0.397 are quite close to those expected for the 3-D Heisenberg model. This proves that ferromagnetic short-range interactions are present in Pr1-xSrxMnO3 compounds. In addition, magnetic-field dependences of |ΔSmax| obey the power law, |ΔSmax| ~ Hn, where the field exponent n ≈ 0.6 is close to the value calculated from the relation n = 1 + (β - 1)/(β + γ).

Large Magnetocaloric Effect Around Room Temperature in Double-Exchange Ferromagnets Pr 1-x Sr x MnO 3 With Short-Range Interactions

High frequency magneto-impedance effect in glass-coated amorphous Co83.2 B3.3 Si5.9 Mn7.6 microwires

In order to investigate the effect of the interface on GMR, [NiFe(25 Å)/Cu(24 Å)]₂/Si thin film was epitaxially grown on HF-treated Si (001) substrate using a DC magnetron sputtering method. Typical GMR effects could be observed in epitaxial film with a weak antiferromagnetic exchange coupling while non epitaxial film showed unsaturated and broad MR curves probably due to inter-diffusion between NiFe and Cu layers. Ferromagnetic resonance (FMR) experiment showed two distinct absorption peaks in all films. Each peak was revealed to come from each NiFe layer with different magnetic property. In FMR measurement, very clear interface in epitaxial films could be confirmed by a lower value of line width (ΔH) and higher Ms of epitaxial film than those of non epitaxial films, respectively.

Seong-Cho Yu

Papers

Thermal treatment at high frequency giant magnetoimpedance in glass coated Co 83.2 B 3.3 Si 15.9 Mn 7.6 microwires

Ferromagnetic Order in Rapidly Cooled Nd-Fe-Co-Al Alloy Ribbons

Large Magnetocaloric Effect Around Room Temperature in Double-Exchange Ferromagnets Pr 1-x Sr x MnO 3 With Short-Range Interactions

High frequency magneto-impedance effect in glass-coated amorphous Co83.2 B3.3 Si5.9 Mn7.6 microwires

Effect of Highly Oriented Layer on GMR and Magnetic Properties of NiFe / Cu Thin Film Prepared by Magnetron Sputtering