The large variety of magnetic phenomena observed in the Co based Laves phases are reviewed. Following the band structure calculations it is argued that the outstanding magnetic features of the RCo2 intermetallics are intimately related to the position of the Fermi level, which is near to a local peak in N(e). This is why the Co 3d-electron system reacts sensitively either to the molecular field of the R partner element or to the changes of external parameters such as a magnetic field or pressure. Magnetic, magnetoelastic and transport measurements of RCo2 compounds and related pseudobinaries such as R(Co1-xAlx)2 with R either magnetic or nonmagnetic rare earth element are shown and discussed. The conditions for the appearance of itinerant electron metamagnetism and spin fluctuations are outlined. In particular, the influences of spin fluctuations on physical properties, e.g. the susceptibility, thermal expansion and transport phenomena, are demonstrated.

https://iopscience.iop.org/article/10.1088/0953-8984/13/23/202/pdf

Physical properties of RCo2 Laves phases

We have studied the magnetic moments and magnetic anisotropy energy (MAE) of YCo5 and SmCo5 using full-potential linear augmented plane wave (LAPW) electronic structure calculations. Most previous calculations of the MAE for YCo5, using local density approximation (LDA) for the exchange-correlation potential, have found values significantly smaller (∼0.6 meV/f.u.) than experiment (∼3.8 meV/f.u.). The rest of the MAE is attributed to many body corrections. Our LAPW calculations using the generalized gradient approximation (GGA) instead of LDA and including nonspherical corrections give values ∼1.5 meV/f.u. The Co magnetic moment of YCo5−xCux, unlike the prediction of the virtual crystal approximation, decreases slowly with impurity concentration until dropping suddenly to zero at a critical dopant concentration. Correlation effects were found to be crucial for the MAE in SmCo5. While GGA calculations give MAE for SmCo5 of the wrong sign, including the LDA+U, correction brings it to ∼21 meV/f.u., in good agreement with the experimental value of 13–16 meV/f.u.

Magnetic properties of SmCo5 and YCo5

Publisher Summary This chapter discusses itinerant electron metamagnetism of Co sublattice in the lanthanide-cobalt intermetallics. The first-order transition (FOT) is observed in several lanthanide-cobalt (R-Co) intermetallics under the effect of varying external parameters and internal parameters. This transition occurs between a nonmagnetic or low-induced moment state and a ferromagnetic state. This phenomenon is called itinerant electron metamagnetism (IEM). The various models to describe IEM are discussed. At the beginning, the basic concepts of the band theory of metamagnetism describing the magnetically uniform states are presented. Then, the role of volume effects and spin fluctuation effects on the metamagnetic behavior are also briefly introduced. The magnetic properties of the systems consisting of both itinerant electrons and localized spins are formulated on the basis of the s-d model. The experimental overview of IEM is given. This section consists of three major parts. The role of the magnetic R-atom as well as the influence of the 3d electrons affecting the character of the magnetic phase transitions and the spin fluctuation scattering is discussed. High-field magnetization in the RCo 2 with one unstable magnetic sublattice is also discussed. IEM in the RCo 3 - and RCo 5 -based compounds is presented.

Chapter 171 Itinerant electron metamagnetism of co sublattice in the lanthanide-cobalt intermetallics

Electronic structures of the pseudo-binary compound with the -type hexagonal structure are calculated in the self-consistent linear muffin-tin orbital method within the atomic sphere approximation, by taking into account the preferential occupation sites for Ni. The calculated bulk moment disappears abruptly near 60% Ni concentration. Above the critical concentration of Ni, a metamagnetic transition from the paramagnetic to the ferromagnetic state is found to occur. These calculated results are consistent with the recently observed ones. It has been shown that the anomalous magnetic behaviours of can be explained by the detailed shape of the local density-of-states curve of the 3d-transition-metal atoms at the 3g site near the Fermi level.

https://iopscience.iop.org/article/10.1088/0953-8984/11/2/013/pdf

Itinerant-electron metamagnetism of

A review is presented on the recent advances of itinerant-electron metamagnetism (IEM). By taking into account the magneto-volume effects, spin fluctuation model for IEM based on the Ginzburg–Landau theory is given. A magnetic phase diagram in this system is obtained for the pressure and temperature. It is shown that the Curie temperature depends strongly on pressure near the boundary between the first-order and second-order transitions, while the spontaneous magnetization at 0 K does not depend so much on the pressure, which is a common property in this system. Other field-induced metamagnetic transitions, e.g., between weakly and strongly magnetic states, between antiferromagnetic and ferromagnetic states and between the narrow-gap semiconductor and the metallic ferromagnet observed in FeSi, are discussed based on the basis of electronic structures obtained by band calculations.

Recent advances of itinerant-electron metamagnetism and related properties of intermetallic compounds

Co metamagnetism and magnetic anisotropy in single-crystalline Ce(Co1 − xNix)5

The magnetization up to 120 T and 10 kbar and magnetostriction up to 40 T have been measured for single-crystalline Ce(Co1−xNix)5 with x ⩽ 0.3. The Co moment is in high moment state for CeCo2 and in low moment state for x ⩽ 0.1. A metamagnetic transition from the low to the high moment state can be induced by applying field up to 120 T for x = 0.1 and 0.2. The relations between the Co moment state and the magnetic characteristics are discussed.

Anomalous magnetic properties due to Co metamagnetism in Ce(Co1−xNix)5

The high-field magnetization and magnetostriction of Ce(Co1−xNix)5 with 0⩽x⩽0.3 have been measured in pulsed fields up to 120 T, together with the magnetization under high pressure. A metamagnetic transition accompanied with a large magnetostriction is observed for x=0.1 and 0.2. The temperature variations of magnetization and anisotropy constant are anomalous and the pressure effect on the magnetization is very large.

A.S. Ermolenko

Papers

Co metamagnetism and magnetic anisotropy in single-crystalline Ce(Co1 − xNix)5

Anomalous magnetic properties due to Co metamagnetism in Ce(Co1−xNix)5

Anomalous magnetic properties of ce(co1-xnix)5 due to co metamagnetism