Showing papers on "Metamagnetism published in 1979"

Density of states and magnetic properties of the rare-earth compounds RFe2, RCO2 and RNi2

Abstract: The density of states of yttrium compounds YM2 (M = Fe, Co, Ni) is calculated within a tight-binding scheme. Using the Stoner model, conclusions are drawn about their magnetic and electronic properties. In YCo2, we show that one has to introduce paramagnon effects in order to explain the electronic properties. The additional d-f interaction introduced by rare-earth atoms (R) in RM2 is treated with a Hartree-Fock approximation. Little change is obtained in iron and nickel compounds. Conversely, in RCo 2 compounds, the exchange field due to the rare-earth atoms can produce collective metamagnetism as described by Wohlfarth and Rhodes [1] and cobalt becomes magnetic. This effect stems from the position of the Fermi level of these compounds in a steep decrease of the density of states. Curie temperature, order of the transition and effect of an external magnetic field are studied following this method. Other consequences are drawn from the model.

Magnetic Properties of Rare Earth Copper Intermetallic Compounds, RCu 2 . II. Light Rare Earth

Abstract: Measurements of magnetization and susceptibility have been made on single crystals of heavy rare earth copper compounds, RCu 2 . All these compounds show metamagnetism with a relative low critical field at 4.2 K. The paramagnetic Curie temperatures along each principal axis are anisotropic. The crystal field parameters V 2 0 and V 2 2 are determined from the values of anisotropic paramagnetic Curie temperatures on the basis of the molecular field theory. These values are in agreement with those evaluated from a point charge model. The neutron diffraction measurements on a TbCu 2 single crystal confirm the collinear magnetic structure.

Polarized neutron study of the itinerant electron metamagnetism in ThCo5

Abstract: The peculiar magnetic properties of the ferromagnetic compound ThCo5 have been studied by means of polarized neutrons. The first order magnetic transition, induced below 150 K by an applied field corresponds to an increase of the magnetization of the two Co sites (2c, 3g). The thermal variations of the spontaneous magnetizations and the superimposed susceptibilities exhibit a maximum at about 170 K. But, adding to the applied field the exchange field due to interactions between the two sites, it appears that only Co atoms of the 3g site exhibit a maximum of the susceptibility, which is reminiscent of the one observed in the Pauli paramagnet YCo2. The results show the character of itinerant electron metamagnetism of the 3g site. Such a property is often observed in compounds where the 3d band is hybridized with less localized d electrons.

Magnetism of the rare earth, 3d { Theoretical review

Abstract: Compounds of rare earth and transition metals exhibit unusual and quite different behaviour. In order to explain the large variety of magnetic behaviour, we show that one needs the electronic structure in these compounds. We report on the existing calculations and give the general shape of the density of states in these intermetallic compounds. We discuss particularly the case of the TM2 compounds (T = rare earth ; M = Fe, CO, Ni). The most unusual behaviour appears with the cobalt compounds where the cobalt within the rare earth serles can be magnetic or not. We review the theories on the TCo2 series and explain the magnetic behaviour by the position of the Fermi level in this compound in a steep decrease of the density of states. This leads to a klnd of collective metamagnetism. This is confirmed by experiments that we review. Unusual behaviour of other compounds wlth cobalt can be understood following the same lines as TCo2 and is discussed.

Itinerant metamagnetism in rare earth-transition metal compounds

Abstract: Intermetallic compounds of rare‐earth and transition metals present the possibility of using the large magnetic moment of the first with the high Curie temperature of the second. We first discuss the nature of the coupling between the spin of the rare‐earth and transition metal. We assume that it happens within the d band coming from the 5d and 3d levels and describe it using the Van Vleck model for ferromagnetism. We then consider the particular case of Cobalt compounds where Cobalt can be magnetic or not depending of the rare‐earth metal. We describe the appearance of magnetism as a collective metamagnetism due to the position of the Fermi level in these compounds in a steep decrease of the density of states. Calculation of the density of states confirms this hypothesis.