J. M. Cadogan

Magnetic properties of a novel Sm3(Fe, Ti)29 phase

Abstract In a systematic study of the Sm 10 Fe 85 Ti x (4.7 x 3 (Fe, Ti) 29 compound has been found to be a new phase, of which the structure is Nd 3 (Fe, Ti) 29 -type. The X-ray diffraction pattern of Sm 3 (Fe 0.933Ti 0.06 7) 29 can be indexed on the monoclinic symmetry with the lattice parameters a = 1.065 nm, b = 0.858 nm, c = 0.972 nm and β = 96.98°. The Sm 3 (Fe 0.933 Ti 0.067 ) 29 compound exhibits ferromagnetic ordering with a Curie temperature T C = 486 K. The saturation magnetization M S is 125 A m 2 /kg at 77 K and 119 A m 2 /kg at room temperature. The room temperature anisotropy field is 3.4 T.

MAGNETIC-PROPERTIES OF A NOVEL SM3(FE, TI)29NY NITRIDE

A new interstitial nitride of Sm3(Fe0.933Ti0.067)29Ny (y=5) has been synthesized. Its x‐ray pattern can be indexed in Nd3(Fe,Ti)29‐type monoclinic symmetry with the lattice parameters of a=1.098 nm, b=0.882 nm, c=0.985 nm, and β=97.50°. The Sm3(Fe0.933Ti0.067)29Ny nitride exhibits ferromagnetic ordering with a Curie temperature Tc=750 K. The saturation magnetization Ms is 160 A m2/kg at 4.2 K and 140 A m2/kg at 293 K. The anisotropy field is 18.1 T at 4.2 K and 12.8 T at 293 K. The coercivity of μ0iHc=0.83 T at 293 K on this new nitride has been developed.

Independent magnetic ordering of the rare-earth (R) and Fe sublattices in the RFe6Ge6 and RFe6Sn6 series

Abstract Magnetic ordering of the rare-earth (R) and Fe sublattices in R–Fe based intermetallic compounds is normally a cooperative phenomenon with the R and Fe sublattices ordering together — at the same temperature. We have recently studied the RFe 6 Ge 6 and RFe 6 Sn 6 compounds using a combination of neutron powder diffraction and Mossbauer spectroscopy (both 57 Fe and 119 Sn). These series show independent magnetic behaviour of the R and Fe sublattices. The Fe sublattice orders antiferromagnetically below a Neel temperature of ∼485 K in RFe 6 Ge 6 and ∼555 K in RFe 6 Sn 6 . The R sublattice orders predominantly ferromagnetically at much lower temperatures, ranging from 45 K for GdFe 6 Sn 6 to 3 K for ErFe 6 Ge 6 , without affecting the Fe order. Here, we review neutron diffraction and Mossbauer work carried out in the study of this magnetic independence.

OBSERVATION OF INDEPENDENT IRON AND RARE-EARTH ORDERING IN RFE6GE6 (R=Y, GD-LU) COMPOUNDS

Mossbauer and magnetization measurements have been used to study magnetic ordering in RFe6Ge6 alloys. The iron sublattice orders antiferromagnetically and TN remains essentially constant across the series at ∼480 K with no evidence of a net magnetization in any of the alloys. For R=Gd−Er, the rare‐earth sublattice orders ferromagnetically with Tc’s that descend from 30 K at Gd to 3 K at Er. This order is established without affecting the order on the iron sublattice. The large difference in ordering temperatures and the unrelated magnetic structures adopted by the two sublattices indicate that the iron and rare‐earth moments are effectively isolated from each other and that they order independently.

Ultrahigh coercive force in epitaxial Fe-Pt(0 0 1) films

Abstract Perpendicular magnetized epitaxial Fe-Pt(0 0 1) thin films with the CuAuI-type structure were prepared by an electron beam evaporation method. The films of about 120–250 A thickness exhibit an ultrahigh coercive force of about 48 kOe at room temperature. These hard magnetic films are mainly composed of fine particles of about 0.1 μm in diameter.

Magnetic properties of new ternary R sub 6 Ga sub 3 Fe sub 11 compounds

Three new rare earth–iron ternary compounds with the La6Ga3Co11 structure (I4/mcm), Pr6Ga3Fe11, Nd6Ga3Fe11, and Sm6Ga3Fe11, are found to be ferromagnetic with Curie temperatures of 320, 397, and 462 K, respectively. Large anisotropies have been observed from the magnetization curves and the anisotropy field is larger than 7 T at room temperature. First‐order magnetization processes were observed for all samples throughout the temperature range of 4.2–300 K. Point charge calculations give A20=1070 K a−20 at the 16l site and −283 K a−20 at the 8f site.

Exchange and crystal‐field interactions in R3(Fe,Ti)29 and R3(Fe,Ti)29Ny (R=Nd,Sm)

A quantitative analysis of the available magnetization data on the R3(Fe,Ti)29 and R3(Fe,Ti)29Ny (R=Nd,Sm) compounds have been carried out. The two R sites of R3(Fe,Ti)29 compounds have opposite signs of their leading crystal‐field coefficient A20; namely, A20<0 for the 4e site (2:17 like) and A20≳0 for the 2a site (1:12 like) (site notation is that of the space group P21/c). A R–Fe exchange coefficient of 285±5μ0 and crystal field coefficients A20(2a)=+16 K a−20 and A20(4e)=−25 K a−20 were obtained. The type‐II first‐order magnetization processes observed in both Nd3(Fe1−xTix)29 and Sm3(Fe1−xTix)29 have been well reproduced: μ0Hcr=2.4 T for R=Nd at 5 K (observed ∼2 T), and μ0Hcr=3.0 T for R=Sm at 4.2 K (∼3.2 T). Based on the bonding charge model, we estimate that the values of A20(4e) and A20(2a) for the fully nitrided 3:29 compounds are A20(4e)=−187 K a−20 and A20(2a)=−184 K a−20. Our calculations show that R3(Fe1−xTix)29Ny nitrides become uniaxially anitsotropic for y≥2 and a maximum room temperature u...

Exchange and crystal field interactions in Sm2Fe17N3−δ

Abstract Exchange and crystal field interactions in Sm2Fe17N3−δ have been studied based on a first-principles model in which the three lowest J-multiplets for the Sm3+ ion were included. A value of (300±5)μ0 for the exchange coefficient nSmFe was deduced from the measured Curie temperature. The KFe1(T) data were determined for Y2Fe17N3−δ from magnetic measurements over the temperature range of 4.2–400 K, and the value of KFe1 at 4.2 K is − 1.3 MJ/m3. A set of the leading crystal field coefficients A20, A40 and A60 has been determined from the best fit to the experimental temperature dependence of the anisotropy field in Sm2Fe17N3−δ. We find that A20 = −(16±5) Ka−2o, A40 = + (8,0±1.0) Ka−40 and A60=−(3.0±1.0) Ka−60.

Magnetic ordering in Er3Cu4X4 (X = Si, Ge, Sn)

Magnetic ordering of the orthorhombic Er3Cu4X4 (X = Si, Ge, Sn) system has been studied using both 119 Sn and 166 Er M¨ ossbauer spectroscopy, combined with neutron diffraction. We observe two distinct ordering events for the erbium moments on the 2d and 4e sites (TN (Er 2d) > TN (Er 4e)) and confirm that the Er 2d moments are larger than those on the Er 4e site. Comparison of neutron diffraction with 166 Er M¨ ossbauer spectroscopy shows that the ordering of the Er 4e moments is far from complete, even at 0.7 TN, causing neutron diffraction analysis to severely underestimate the Er 4e moments in the Er3Cu4X4 system.

Magnetization curves of a Tb/sub 3/(Fe,V)/sub 29/ single crystal

A Tb/sub 3/(Fe,V)/sub 29/ single crystal has been grown using the Czochralski method. Magnetization measurements along the hard axis of the crystal are presented. At low temperatures, a first-order magnetization process of type II occurs at large critical fields (/spl mu//sub 0/H/sub c/=10.6 T at T=5 K). The data were analysed using the first-principle model in terms of exchange and crystal-field interactions. The second order crystal-field coefficients of two rare earth sites are estimated to be A/sub 20/=-36K.a/sub 0//sup -2/ for the 4i site, and A/sub 20/=+16K.a/sub 0//sup -2/ for the 2a site.