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A strong effect of pressure on magnetization and paramagnetic moment of the Co-doped Mn-rich Ni50-xCoxMn25+yGa25-y (x = 5,7,9 and y = 5,6,7,8) Heusler alloys is presented and compared with very weak pressure sensitivity of magnetization of the stoichiometric Ni2MnGa alloy. The effects of both, the pressure and the magnetic field, on temperature of the structural martensitic transition in the alloys are discussed with a use of the Clausius-Clapeyron relations. An analysis of pressure and field effects provides a possibility to evaluate structural and magnetic parts of latent heat of the martensitic transitions in the studied alloys. The Curie temperature of martensite phase of the Co-rich alloys is not affected by pressure.

Abstract: Recently, an attention has been paid to outstanding magnetic properties of martensitic phase of the Co-doped Heusler Ni2MnGa alloys with a paramagnetic gap that can be tuned by composition. We have prepared polycrystalline sample of Co doped Ni2MnGa alloy, Ni43Co7Mn31Ga19, with the very small amount of Er (0.1at.%). By the EDX analysis, a distinct segregation of Er was discovered in Er-rich phase while the main bulk material of the microcrystals was totally Er-free. Saturated magnetization M(5K)=3.27μB/f.u. and the Curie temperatures of austenite phase, were observed by a SQUID magnetometer on annealed sample and the standard magnetocaloric effect at vicinity of was measured by direct method with ΔT =0.6K. Magnetic susceptibility obeys nicely the Curie-Weiss law with paramagnetic moment of μ eff =5.09μB/f.u. above . However in the pronounced contrast with the Er-free alloys, both, the paramagnetic gap and mainly the martensitic transitions were not observed in the Er conditioned Ni43Co7Mn31Ga19 sample. [Copyright &y& Elsevier]

We have studied the development of the magnetocaloric effect in the (Tb,Y)NiAl and TbNi(Al,In) series as determined from magnetization measurements. The transition from antiferromagnetic order in TbNiAl to ferromagnetic order in Tb0.7Y0.3NiAl is accompanied by increase of the maximum entropy change from - 4.1 to - 4.4 J kg-1 K-1. In the TbNi(Al,In) series, the change of uniaxial anisotropy in TbNiAl to the easy-plane anisotropy in TbNiIn leads to broadening of the magnetocaloric effect accompanied with large increase of the relative cooling power from 66 to 120 J kg-1. [ABSTRACT FROM AUTHOR]

To show and to describe a contrast between the magnetic and structural properties of the stoichiometric Ni2MnGa alloy and the off-stoichiometric and the Co-doped Ni-Mn-Ga alloys, we report the effect of high hydrostatic pressure (up to 1.2GPa) on magnetization and the critical temperatures of structural and magnetic transitions in the off-stoichiometric Ni50-xMn25+x+yGa25-y and the Co-doped Ni50-xCoxMn25+yGa25-y Heusler alloys. A huge decrease in their saturation magnetization MM(5K) under pressure was observed with an extreme value of pressure parameter dlnMM(5K)/dP=-56×10-3GPa-1 in the case of the Ni39Co11Mn34Ga16 alloy. The Curie temperature TCA increases under pressure in all the studied alloys. Almost identical values of dTCA/dP=+4.7÷+5.9KGPa-1 point to a normalized steepness of a dependence of exchange interactions on interatomic distances. The values of paramagnetic effective moments, meff, are identical in both structural phases of the alloys and they lie in a narrow interval from 4.6µB to 5.7µB. Furthermore, the Co-doped alloys show a very strong pressure dependence on the structural critical temperature TM-A, with values of dTM-A/dP up to +34KGPa-1, the highest reported values for the Ni-Mn-based Heusler alloys. The results are discussed in light of the fundamental magnetic interactions in the Heusler alloys and from the point of view of a further exploration of their multifunctional applications. [ABSTRACT FROM AUTHOR]

In addition to complex spin-ice and spin-liquid states of rare-earth pyrochlore oxides, A 2 Ir 2 O 7 iridates have been recently proposed to host a cooling-field-controllable antiferromagnetic domain structure of iridium moments. Reliable and profound studies of the magnetic domain structure, including domains' interfaces, have been frequently limited by insufficient sample quality or lack of single crystals. We report the magnetic properties of the for-the-first-time synthesised Lu 2 Ir 2 O 7 and Er 2 Ir 2 O 7 single crystals; focussing on the robust ferromagnetic component of magnetisation present in the material with the antiferromagnetically ordered state of the all-in-all-out (AIAO) type. Anisotropy of the system, as well as the effects of magnetic (Er 3+ ) or nonmagnetic (Lu 3+ ) local environments on Ir 4+ moments, is studied. The size of the domains is calculated based on a simplified domain wall model. Results are discussed in the framework of AIAO and AOAI domains and interfaces on the geometrically frustrated lattice., (© 2024. The Author(s).)

We have performed a quantum-mechanical study of a series of stoichiometric Ni2MnSn structures focusing on pressure-induced changes in their magnetic properties. Motivated by the facts that (i) our calculations give the total magnetic moment of the defect-free stoichiometric Ni2MnSn higher than our experimental value by 12.8% and (ii) the magnetic state is predicted to be more sensitive to hydrostatic pressures than seen in our measurements, our study focused on the role of point defects, in particular Mn-Ni, Mn-Sn and Ni-Sn swaps in the stoichiometric Ni2MnSn. For most defect types we also compared states with both ferromagnetic (FM) and anti-ferromagnetic (AFM) coupling between (i) the swapped Mn atoms and (ii) those on the Mn sublattice. Our calculations show that the swapped Mn atoms can lead to magnetic moments nearly twice smaller than those in the defect-free Ni2MnSn. Further, the defect-containing states exhibit pressure-induced changes up to three times larger but also smaller than those in the defect-free Ni2MnSn. Importantly, we find both qualitative and quantitative differences in the pressure-induced changes of magnetic moments of individual atoms even for the same global magnetic state. Lastly, despite of the fact that the FM-coupled and AFM-coupled states have often very similar formation energies (the differences only amount to a few meV per atom), their structural and magnetic properties can be very different.