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

In this work, the magnetic and magnetocaloric properties of La0.7Ba0.25Nd0.05Mn1-xCuxO3 samples (x = 0 - 0.07) synthesized by the sol-gel method are presented. The compounds exhibited a second-order phase transition (SOPT) of ferromagnetic-paramagnetic (FM-PM) phase transition following Banerjee’s criterion. Curie temperature TC decreased with increasing doping concentration. The critical behavior analysis using modified Arrott plots (MAP) showed a short-range FM ordering. Significant entropy change of samples was observed near the TC, which decreased with Cu content. The SOPT nature of compounds was confirmed by both the universal curves and scaling hypothesis.

Critical behavior and magnetocaloric effect in La0.7Ba0.25Nd0.05Mn1-xCuxO3

We explore further details of the collectively excited spin wave mode in finite arrays of elliptically shaped ferromagnetic nanoelements as two-dimensional magnonic crystals by means of micromagnetic simulations. Under a pulsed magnetic driving field, collective spin wave modes were intensively investigated with variation of nanoelement dimensions and interelement separation as structural parameters of the magnonic crystal as well as changing the applied bias magnetic field. Via observing and analyzing the dynamic behavior of collective spin wave modes, we have found that the dynamic behavior strongly depends on the bias magnetic field with a quasi-linear dependency. The quasi-linear dependency of spin wave frequency transition can be achieved to a high sensitivity of the pT/Hz level. By modulating the magnonic crystal lattice structures and the bias magnetic field, the spin wave dynamic behavior is tunable which might be a promising property for a future magnonic crystal application and multifunctional sensors.

Collective spin excitation in finite size array of patterned magnonic crystals

A Study of Two Magnetic Phases in a Co-Cu Magnetic Granular Alloy

Influence of Annealing Conditions on Microstructural, Luminescent and Magnetic Properties of PLD-grown ZnO Films

The magnetic entropy behavior has been analyzed in the double-perovskite Ba2-xLaxFeMoO6 (x = 0, 0.1, 0.2) compound with the sintering temperature. Samples were fabricated by conventional solid-state reaction method. The results show that the values of ΔSM are increased with increasing sintering temperature from 1273 K to 1473 K. The values of ΔSM for Ba2-xLaxFeMoO6(x = 0) are increased about five times with increasing sintering temperature, especially. The enhancement of the magnetic entropy change is believed to be due to a strong coupling between spin and lattice in the magnetic transition process near Curie temperature. Our result reveals that the proper sintering of perovskite Ba2-xLaxFeMoO6 compound makes it one of the useful methods for the development of advanced magnetic refrigeration materials.

Seong-Cho Yu

Papers

Critical behavior and magnetocaloric effect in La0.7Ba0.25Nd0.05Mn1-xCuxO3

Collective spin excitation in finite size array of patterned magnonic crystals

A Study of Two Magnetic Phases in a Co-Cu Magnetic Granular Alloy

Influence of Annealing Conditions on Microstructural, Luminescent and Magnetic Properties of PLD-grown ZnO Films

The Variation of Magnetic Entropy on ${\rm Ba}_{2-{\rm x}}{\rm La}_{\rm x}{\rm FeMoO}_{6}$ Compound With the Sintering Temperature