K.H.J. Buschow

Study of the critical behaviour of the magnetization and electrical resistivity in cubic La(Fe, Si)13 compounds

Abstract The magnetic properties of the cubic NaZn 13 type pseudobinary compounds La(T x Si 1- x ) 13 were studied for T = Fe, Co and Ni in the temperature range 4.2–300 K. 57 Fe Mossbauer spectroscopy was performed on LaFe 11 Si 2 and 57 Fe-doped LaCo 11 Si 2 . The compounds with T = Fe or Co are ferromagnetic, while the compound LaNi 11 Si 2 is a Pauli paramagnet. The critical behaviour around the Curie temperature T c was studied in La(Fe x Si 1- x ) 13 by measuring the temperature dependences on the zero-field susceptibility and the electrical resistivity. The critical exponent γ in the expression χ ∝ ( T - T c ) -γ was found to be close to 1.38 corresponding to an isotropic Heisenberg ferromagnet. The anomalous critical behaviour shown by electrical resistivity can be explained in terms of lattice softening associated with the Invar effect.

Magnetic Susceptibilities of Rare‐Earth–Indium Compounds: RIn3

The magnetic properties and the lattice parameters for 13 compounds of the composition RIn3 (Cu3Au structure) are reported. The magnetic measurements have been performed between 4.2° and 500°K with magnetic fields up to 30 kOe. With the exception of compounds with R=La, Sm, Y, and Yb Curie–Weiss behavior is observed in the high‐temperature region. At low temperatures the magnetic behavior for compounds in which R=Ce, Nd, Sm, Gd, Tb, Dy, Ho, and Er is ascribed to antiferromagnetic ordering. In the case of PrIn3 magnetic ordering is prevented by crystalline fields. The splitting of the Ju2009=u20094 state of Pr3+ by cubic crystalline fields has been calculated for various combinations of fourth‐ and sixth‐order potentials. Possible energy diagrams are presented.

Magnetic and electrical properties of several equiatomic ternary U-compounds

Magnetisation, specific heat, electrical resistivity, magnetoresistivity and Hall effect were measured for several equiatomic ternary (1-1-1) intermetallic compounds of formula RTX with R = U, Th, Hf and Ti, T a transition metal (Co, Ni, Ru, Rh, Pd, Ir, Pt and Au), and X = Al, Ga, Sn and Sb. These compounds crystallize in three different crystal structures: the cubic MgAgAs-type, and the hexagonal Fe2P- and CaIn2-types. All U-compounds, which we focus upon in this paper, exhibit magnetic moments of about 3μB/U at high temperature and encompass U-U distances from 3.51 to 4.68 A. For the compounds which the largest U-U distances, Kondo-lattice behaviour was observed. The specific heat coefficient γ shows typical metallic values with some enhancement. Remarkably these compounds have an electrical resistivity up to three orders of magnitude larger than that expected and usually found for U-based intermetallic compounds. The Hf- and Th-based compounds serve as nonmagnetic reference materials, however, they also exhibit anomalously larger resistivities.

Influence of s-f exchange interaction on electrical conduction in rare-earth dialuminides

Abstract The electrical resistivity has been measured between 4.2 and 300°K for RA1 2 compounds, where R denotes the rare-earth elements La, Ce, Pr, Nd, Gd, Tb, Dy, Ho, Er, Yb and Y. From an analysis of the resistivity behaviour of the ferromagnetic compounds values are deduced for the effective s-f exchange coupling constants. These values agree reasonably well with data given in literature for the Knight shift of the A1 nuclear magnetic resonance. For CeA1 2 a resistivity minimum has been observed at 13°K.

MAGNETIC PROPERTIES OF RARE EARTH TETRABORIDES.

The magnetic properties and the lattice constants of the rare earth tetraborides RB4 have been determined. The compound PrB4 is ferromagnetic. The compounds in which R represents Nd, Sm, Gd, Tb, Dy, and Ho are antiferromagnetic while ErB4 and YbB4 show metamagnetic behavior. The element Ce and to some extent also the element Yb show an abnormal valency in the tetraborides. The magnetic properties of the RB4 compounds are discussed in terms of the RKKY formalism. It is shown that the ferromagnetic behavior of PrB4 is probably the result of a strong participating of the orbital angular momentum to the indirect exchange coupling between the localized moments.

Investigations on the resistivity of the compound CeAl3

Abstract The electrical resistivity of the compound CeAl3 between 1.3 and 280°K has been observed to behave markedly anomalous. Further information concerning the nature of this anomaly has been obtained from data on the resistivity of compounds Ce1−xRxAl3, R denoting La or Th.

Permanent magnets with energy products of 20 million gauss oersteds

Abstract Compounds corresponding to the Co-rich part of the SmCo 5 homogeneity region have been used to obtain permanent magnets with energy products larger than 20 × 10 6 G.oe. The stability is discussed.

Electrical Transport Properties of the Ternary Compounds UTSn, UTSb and ThTSn

Abstract The resistivity of the equiatomic ternary compounds UTSn, UTSb and ThTSn is up to two orders of magnitude larger than Mooijs criterion: ϱ max =250 μΩcm. An exponential decrease of the resistivity at high temperatures suggest a band-gap in spite of the relatively high values for the linear specific heat coefficient γ.

Magnetic properties of cubic La(FexAl1−x)13 intermetallic compounds

We report susceptibility and magnetization measurements for La(FexAl1−x)13 which can be stabilized over the x range 0.46–0.92. At low x values a mictomagnetic regime occurs with distinct cusps in the ac susceptibility. Upon increasing the Fe concentration a soft ferromagnetic phase is found which at lower temperatures shows anisotropy effects related to mictomagnetic behavior. Finally for x>0.86 antiferromagnetic order appears along with a very sharp metamagnetic transition in external fields of a few Teslas. The saturation moment increases linearly with x from 1.3μB to 2.3μB throughout the ferro‐ and metamagnetic regimes. These unusual properties are discussed in terms of local moment magnetism and the particular crystal structure which permits a large Fe‐Fe coordination number at small distances.

Nuclear Magnetic Resonance in Rare‐Earth—Aluminum Intermetallic Compounds: RAl3

The Knight shifts of the 27Al NMR in LaAl3, CeAl3, PrAl3, NdAl3, GdAl3, and TbAl3 have been measured at temperatures from 78° up to 450°K. The effective exchange constants J between the 4f electrons localized at the rare‐earth ions and the conduction electrons at the Al nuclei have been derived to be −0.2 eV. Ruderman—Kittle—Yosida periodic oscillations of the conduction electron polarization have been used to relate the results with those obtained for RAl2. Nuclear quadrupole coupling constants have been measured to be |e2qQ|=0.8 Mc/sec. On the basis of the ionic point model e2qQ has been calculated for RAl3 and RAl2.