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

Sm1−xSrxMnO3 (SSMO) with x ∼ 0.44 shows a multi-critical phase diagram which includes antiferromagnetic, charge ordering, and ferromagnetic transitions that give rise to large magnetoresistive and magnetocaloric effects. In this study, we systematically investigated the magnetic transitions, magnetocaloric effect (MCE), and refrigerant capacity (RC) in polycrystalline Sm1−xSrxMnO3 (x = 0.42, 0.44, 0.46) samples prepared by a standard ceramic method. Magnetization measurements and Arrott plot analyses reveal a first-order ferromagnetic transition for all samples investigated, with TC = 130 K, 134 K, and 133 K for x = 0.42, 0.44, and 0.46, respectively. The largest peak entropy change of −ΔSM = 4.61 J/kg K for a field change of μ0ΔH = 5 T is observed for the x = 0.44 composition around its Curie temperature of 134 K. After correcting for hysteretic losses of ∼15% – 30% engendered by the first order nature of the transition, sizable RC values of 151.42 J/kg, 140.15 J/kg, and 135.91 J/kg are still observed fo...

Magnetocaloric effect and refrigerant capacity in Sm1−xSrxMnO3 (x = 0.42, 0.44, 0.46) manganites

Time resolved photoluminescence spectra of natural MgAl2O4 spinel doped with Cr3+ ions have been investigated at room temperature in the wavelength range between 380 and 800 nm. Using several excitation sources from the different lasers we have observed a new band, namely K, with a peak of 15,547 cm−1 (643.2 nm) and the transition process of photoluminescent lines among the electronic levels of the Cr3+ ion. In terms of the experimental results and the Tanabe-Sugano diagram, we strongly propose that the K-band originates from the electric dipole transition, 2Eg 4A2g in the strong crystal field with Dq/B > 2.3. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A new band in Cr3+-doped MgAl2O4 natural spinel at room temperature

We have studied the magnetic and spin-glass (SG) properties of La0.7Ca0.3MnO3 single-crystalline nanoparticles, which were prepared by the mechanical milling method with different milling times (tm). Analyzing the susceptibility data in the paramagnetic region indicates both ferromagnetic (FM) and anti-FM interactions coexisting in nanoparticles. Additionally, there is a peak associated with the freezing temperature (Tf) appearing on the real part curve of the ac susceptibility, χ′(T). The Tf value increases with increasing frequency as expected for SG systems. The SG behavior was also checked by using the criterion parameter c = ΔTf/TfΔ(log10f), and the power law τ = τ0(T/Tg − 1)−zν. The obtained values of c ≈ 5 × 10−2, τ0 ≈ 10−5 s and zν ≈ 2–3 are consistent with those expected for SG-like systems, suggesting an existence of a SG phase transition at Tg below Tf, which decreases with decreasing ⟨D⟩. Basing on ln(f) versus Tf data, and the Neel-Arrhenius model [ln(f) = ln(f0) - Ea/kBT] and Vogel–Fulcher l...

Coexistence of considerable inter-particle interactions and spin-glass behavior in La0.7Ca0.3MnO3 nanoparticles

Asymmetric GMI characteristics in current-biased amorphous (Co0.94Fe0.06)72.5Si12.5B15 wire

The magnetization behavior and magnetic caloric effect have been analyzed for amorphous Fe 93− x Nb 7 B x (numbers indicate at.%; x  = 9, 14, 20) alloys. An amorphous phase was formed after quenching by melt spinning with a copper wheel surface speed of 30 m/s. The magnetization measurements of the samples were performed by vibrating sample magnetometer. The Curie temperature increased from 299 to 419 K with increasing B concentration ( x  = 9–20). Temperature dependence of the entropy change, Δ S M was calculated from the isothermal magnetization. The values of Δ S M are 1.44, 1.07 and 0.97 J/kg K at x  = 9, 14 and 20, respectively. The maximum of Δ S M was found to appear in the vicinity of the Curie temperature in these alloy samples.

Seong-Cho Yu

Papers

Magnetocaloric effect and refrigerant capacity in Sm1−xSrxMnO3 (x = 0.42, 0.44, 0.46) manganites

A new band in Cr3+-doped MgAl2O4 natural spinel at room temperature

Coexistence of considerable inter-particle interactions and spin-glass behavior in La0.7Ca0.3MnO3 nanoparticles

Asymmetric GMI characteristics in current-biased amorphous (Co0.94Fe0.06)72.5Si12.5B15 wire

The magnetization behavior and magnetocaloric effect in amorphous Fe–Nb–B ribbons