E. Tomey

Role of the (H,C,N) interstitial elements on the magnetic properties of iron-rare earth permanent magnet alloys

Abstract A comparison is made between the intermetallic compounds R2Fe14B, R2Fe17 and RFe12−xMx (R = rare earth metal and M = Ti, Mo) and their interstitial derivatives (hydrides, carbides and nitrides). The role of the different interstitial elements on the magnetic properties will be reviewed through their crystal structure (in particular the localization of the interstitial) and through experimental work done by magnetic susceptibility, Curie point measurements and neutron diffraction.

Influence of hydrogen on the structural and magnetic properties of the RFe10.5Mo1.5 compounds (R=rare earth)

Abstract The structural and magnetic properties of RFe 10.5 Mo 1.5 alloys and their hydrides were studied using X-ray diffraction and magnetic measurements. Hydrogen occupies the octahedral interstitial 2b site of the tetragonal ThMn 12 -type structure (space group I4/mmm, Z = 2 ), which allows a maximum uptake of one hydrogen atom per formula unit. The unit cell volume expands about 1% and the Curie temperature is increased about 10% by the hydrogen uptake. The mean magnetic moment of the iron sublattices is increased. On hydrogenation, (i) the magnetocrystalline anisotropy of the 3d sublattice is enhanced, (ii) in the compounds containing the R elements with a positive second-order Stevens factor α J , the c -axis is the easy axis, and (iii) for the compounds with R having a negative second-order Stevens factor, the easy direction lies in the ab -plane. The Dy and Tb alloys show temperature induced spin reorientation transitions (SRT). On hydrogen uptake, their hydrides have a basal plane behaviour. This change in the series can be understood by the donor character of H together with a narrowing of the 3d metal bands induced by the volume expansion.

Neutron diffraction and magnetization studies of ErFe/sub 10.5/Mo/sub 1.5/D/sub x/ (x=0, 0.9)

A powder neutron diffraction and magnetic measurements have been performed on the ErFe/sub 10.5/Mo/sub 1.5/D/sub x/ compounds (x=0, 0.9). The results allow to locate the deuterium atoms in the structure and to determine the magnetic structures of these compounds. >

Effects of interstitials on the transition metal sublattice anisotropy in YFe/sub 10.5/Mo/sub 1.5/Z/sub x/(Z=H, N; x/spl ap/1)

The effects of interstitial atoms in rare earth (R) intermetallic compounds are: strong increase in Curie temperature, weak increase of saturation magnetization and large influence in the crystalline electric field (CEF) at the R atom. These effects are more remarkable in carbide and nitride compounds than in hydrides. In this paper we will show that additional effects concerning the transition metals (T) occur. In YFe/sub 10.5/Mo/sub 1.5/, with ThMn/sub 12/-type structure, it is shown that the introduction of H or N leads, also to an increase of both the Curie temperature and Fe moment. The most remarkable effect is that whereas with hydrogen we observe an increase of the easy c-axis anisotropy, with nitrogen the anisotropy becomes easy plane. >

Hydrogen insertion effects on the structural and the magnetic properties of the RFe10.5Mo1.5 compounds (R = rare-earth metals)

Abstract The structural and magnetic properties of the RFe 10.5 Mo 1.5 alloys and their hydrided derivatives have been extensively studied using X-ray, neutron diffraction and magnetic measurements. In this paper we discuss the impact of hydrogen insertion on the fundamental magnetic characteristics such as magnetisation, exchange couplings and magnetocrystalline anisotropy.

Relationship between the structural and magnetic properties of the series RFe10.5Mo1.5Xx with X = H, C, N and 0 ≤ x ≤ 1

Abstract The cell parameter expansions and the atom positions in the crystal structure of the RFe 10.5 Mo 1.5 X x series (X = H, C, N; 0 ≤ x ≤ 1) depend strongly on the nature, size and concentration of interstitial elements. Magnetic measurements reveal direct correlations between the Curie temperature, the increase in magnetisation and the crystal structure modifications. The change in the magnetocrystalline anisotropy is found to be dependent on the nature of X.

Magnetic properties of RFe10.5Mo1.5 single crystals (R = Dy, Er)

Abstract Magnetization measurements of tetragonal DyFe 10.5 Mo 1.5 and ErFe 10.5 Mo 1.5 single crystals are presented. In both materials, below T c , magnetization is along c down to a spin reorientation temperature, T ST = 175 K and 53 K, respectively. Below T ST magnetization becomes intermediate between c and the basal plane. The hard axes are [100] and [110] for Dy and Er, respectively.

Transition metal distribution in the ErMn12−xFex (0 ⩽ x ⩽ 8) compounds

Abstract High-resolution neutron diffraction patterns have been collected at room temperature using ILL facilities for various ErMn 12− x Fe x compounds. Samples of composition x = 0, 2, 4, 6, 8 have been analysed in terms of the relative distribution of the transition metal (Mn or Fe) on the three available 8i, 8j and 8f sites of the structure type (SG: I4/mmm). Refinements of the crystal structures show that Mn atoms accommodate preferentially the 8i site contrarily to Fe atoms that fill majority the 8f ones. This observation is consistent with the criterial of relative atom size.

Effects of interstitials on the transition metal sublattice anisotropy in YFe/sub 10.5/Mo/sub 1.5/Z/sub x/(Z=H, N; x≅1)

The effects of interstitial atoms in rare earth (R) intermetallic compounds are: strong increase in Curie temperature, weak increase of saturation magnetization and large influence in the crystalline electric field (CEF) at the R atom. These effects are more remarkable in carbide and nitride compounds than in hydrides. In this paper we will show that additional effects concerning the transition metals (T) occur. In YFe/sub 10.5/Mo/sub 1.5/, with ThMn/sub 12/-type structure, it is shown that the introduction of H or N leads, also to an increase of both the Curie temperature and Fe moment. The most remarkable effect is that whereas with hydrogen we observe an increase of the easy c-axis anisotropy, with nitrogen the anisotropy becomes easy plane. >