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Magnetic refrigerants are used as heat exchangers to provide rapid heat transfer between magnetocaloric materials and heat-transfer liquid. An important question is how to turn bulk magnetocaloric materials into porous structures with superior heat transfer properties and cooling performance. We discuss two methods for assembling Y2Fe17 rapidly quenched ribbons into heat exchangers of desired geometry stacked 100 mm thick plates with 100 mm gaps: the first method consists in gluing rapidly quenched ribbons using thermoconductive epoxy; the second is sintering stacked ribbons at a temperature of 30 K below the melting point of the Y2Fe17 phase. These approaches are promising with regards to making near-net shaped magnetic refrigerants. We report on adiabatic temperature change Delta T-ad, magnetic entropy change Delta S-m and thermal conductivity lambda of rapidly quenched Y2Fe17 ribbons, obtained at different quenching rates. A direct correlation between the lattice parameters of the Y2Fe17, Delta T-ad and Delta S-m in rapidly quenched samples is observed. (C) 2016 Elsevier B.V. All rights reserved.

This paper presents the study of the magnetic properties and magnetocaloric effect (MCE) of the rare-earth ferrimagnetic Dy 2 Fe 10 Al 7 compound. The field and temperature dependencies of the magnetization in the temperature range 4.2–300 K were studied in magnetic fields up to 100 kOe. The MCE was studied by direct method in magnetic fields up to 70 kOe. It was established that the sign of the MCE changes from positive to negative near the compensation temperature. It was shown from the obtained experimental results and the theoretical estimations that the temperature and field dependencies of the MCE in rare-earth ferrimagnet differ from those in ferromagnetic materials. The effective field ( H eff 2 ) determined from the values of the MCE near to the compensation temperature are in a good agreement with those reported earlier.

A study on the magnetocaloric effect (MCE) has been carried out on the HoCo 5 single crystal using a direct method in the temperature range 78–300 K and in a magnetic field of 1.3 T at various orientations of the single crystal with respect to the direction of external magnetic field. Our research has shown that magnetic anisotropy strongly affects magnitude and sign of the MCE in the regions of spin-reorientation phase transitions. In addition, the magnetic domain structure of the HoCo 5 single crystal in (0 0 1) plane in the temperature range from room temperature down to 4.2 K was investigated.

The magnetic domain structure on (1 0 0), (1 1 0), (0 0 1) and arbitrary oriented planes of the R(FeCo) 11 Ti single crystals (R = Dy, Tb) is investigated. The role of the stress-induced magnetic anisotropy in the DS formation and the spin-reorientation transitions is analyzed. It is shown that the magnetoelastic contribution to the anisotropy in these compounds is large and can cause changes of the spin-reorientation temperatures and special domain patterns formation.

Magnetization and anisotropy field of Nd2Fe14−xCoxBH4.1 (x=0–8) hydrides have been measured on powder aligned specimens. It was found that the unit cell volume increases after hydrogenation. At room temperature all compounds show “easy axis” anisotropy and “easy cone” anisotropy at temperatures below the spin-reorientation temperature (TSR). TSR of the initial compounds and hydrides decreases by the replacement of Fe by Co. Hydrogen insertion in the crystal lattice of Nd2Fe14−xCoxBH4.1 leads to a decrease of TSR by 15 K at Co concentrations x ⩽ 6 . The anisotropy field at room temperature decreases under hydrogenation. We can conclude that the replacement of Fe by Co causes both the unit cell volume and TSR decrease. The TSR decrease is determined by a change of electron structure and magnetocrystalline anisotropy rather than by a decrease of the unit cell volume with the Co concentration increasing.

In ternary R 3 Fe 33 - x Ti 3 ( x = 0 , 1 , … , 7 , R = Gd , Y ) and R 3 Fe 33 - x Ti 3 ( R = Tb , Ho , Dy , Er , x = 0 , 3 , 6 , 9 ) alloys, the anomalous wide homogeneous region of ThMn12 structure has been obtained. The single-crystal samples for each composition R3Fe33−xTi3 were prepared. By means of thermomagnetic analysis, it is shown that the TC of these single crystals monotonically decreases with the decrease in Fe concentration. With the decrease of iron concentration, the magnitude of magnetization saturation steadily decreases too. On the other hand, the temperatures of spin reorientation phases transition TSR for R = Tb , Ho , Dy , Er increase. From this, it follows that by the small changes in the Fe concentration it is possible to make a significant change of parameters of exchange interaction between R and 3d sublattices.

The tetragonal ThMn 12 -type, single crystalline DyFe 10 CoTi sample has been investigated by torque and magnetization measurements and observation of domain structure at various temperatures between 10–300 K and in magnetic field from B =0 to 0.15 T. These examinations showed that the magnetic structure of DyFe 10 CoTi changes from “easy axis” ( c -axis) type to conical at 225 K and to “easy plane” ( ab plane) type at 100 K.

The effect of the substitution of Co for Fe on the magnetic anisotropy in YTiFe11−xCox (0≤x≤5) single crystals has been studied by using torque and vibrating-sample magnetometry techniques. The K1 and K2 values were calculated. The Co ion gives a resultant anisotropy which is opposite to that of Fe. A competition is expected to take place in the composition range 5

The aim of this work is to study the influence of substitution of Co for Fe on the magnetocrystalline anisotropy and spin reorientation transition in TbFe 11− x Co x Ti ( x =0;0.5;1;2;3;4;5) compounds. The anisotropy study has been performed by means of torque and magnetization measurements on single crystal samples. It was shown that increase of the Co content in Tb(FeCo) 11 Ti compounds leads to an increase of the Curie temperatures T c . The temperature of the magnetic phase transition during which the easy magnetic direction (EMD) changes from the c-axis via a cone to the basal plane has been found to decrease with increasing Co concentration. On the basis of the experimental results a T − x magnetic phase diagram was constructed. The appearance of phase transitions can be explained by the temperature-dependent competition between the planar Tb sublattice anisotropy and the transition metal (FeCo) 11 sublattice anisotropy.

The magnetic domain structure of Fe14Nd2B single crystals has been studied from room temperature down to 4.2 K by means of the magneto-optical Kerr effect. It was found that the coercivity of different domain walls essentially depends on their type and orientation. The general expressions for the domain wall energy density γ have been performed for Fe14Nd2B compounds in the low-temperature region. The role of the new domain wall types in the low-temperature magnetization reversal process in FeNdB permanent magnets is discussed.

Crystallographic structure, domain structure and magnetic properties of ternary Gd 3 Fe x Ti 3 ( x =34, 33, …, 24), TbFe 11 Ti and TbFe 10 Ti alloys and single crystals are investigated. It is shown that all these compounds have a ThMn 12 tetragonal crystal structure. The wide homogeneous region for the ThMn 12 structure detected for this group of compounds is used to explain the differences in the values of spin-reorientation temperatures of RFe 11 Ti compounds found by different authors.

The angular dependence of the nucleation field H n in high-coercivity grains of sintered NdFeB and SmCo 5 magnets has been studied by direct observations of the domain structure in an external magnetic field. The effect of the stray field of surrounding grains on the angular dependence of H n has been estimated quantitatively. It is found that changes in H n of individual grains as large as 0.45 T may be observed, depending on the micromagnetic state of neighbouring grains.

Thermal remagnetization was studied on samples with different M H c distribution. The process is computer simulated on the basis of a model for which the internal magnetic field distribution is calculated with given experimental M H c distribution and M H c and M s temperature dependence. Peculiarities of the open-circuit thermal remagnetization of non-ellipsoidal magnets are examined.

The magnetization reversal behaviour of individual grains was studied by direct domain structure observations. On this basis the angular dependence of the saturation field Hs, critical field of reverse domain removal, Hk, and nucleation field Hn was found to obey the law 1/cos(ϕ − ϕm), where ϕm is the angle between the grain easy axis and the axis of magnet texture.