R.S. Eccleston

Exchange interactions in GdFe compounds studied by inelastic neutron scattering

Abstract Inelastic neutron scattering (INS) has been used to study the exchange interactions in polycrystalline samples of GdFe2, GdFe3, Gd3Lu3Fe23, Gd2Fe14B, Gd2Fe14C, Gd2Fe17, GdFe10Si2 and GdFe10.6V1.4. Direct values of the molecular fields experienced by the Gd moments and — by using a simple spin wave model — the Gd Fe exchange constants in these compounds were obtained from the position of the dominant transition at low momentum transfer in the INS spectra. The results of the molecular fields are compared with values derived from the high-field free powder (HFFP) method, and with the results of band structure calculations.

Intersublattice exchange coupling in Gd–Mn compounds studied by INS

Abstract Inelastic neutron scattering (INS) has been used to study the exchange interaction in polycrystalline samples of GdMn2Si2, GdMn2Ge2, GdMn6Sn6 and Gd6Mn23. Direct values of the molecular fields experienced by the Gd moments were obtained from the position of the dominant transition at low momentum transfer in the INS spectra. By using a simple spin wave model, also values of the Gd–Mn exchange constants in these compounds were derived. Our results are compared with results from different magnetic measurements.

Intersublattice exchange coupling in Gd-Co compounds studied by INS

Abstract Inelastic neutron scattering (INS) has been used to study the intersublattice interaction in GdCo 2 , GdCo 5 , Gd 2 Co 14 B, Gd 2 Co 17 , and GdCo 10 V 2 . Direct values of the molecular fields experienced by the Gd moments in these compounds were obtained from the single transition at low momentum transfer in the INS spectra.

Nitrogen-induced reduction of the Gd-Fe exchange coupling in Gd2Fe17Nx

Abstract The compound Gd,Fe,, and its ternary nitride Gd,Fe,,N, were investigated by means of inelastic neutron scattering. The values determined for the molecular field acting on the Gd3+ ions are Bmol = 285 T and B,,, = 199 T, respectively. These values show that nitrogen up-take in Gd,Fe,, leads to a marked reduction in the magnetic intersublattice coupling strength. Intermetallic compounds formed with rare earths (R) and 3d metals are an interesting class of materials because they can combine a high magnetic ordering temperature and a high mag- netization due to the 3d sublattice with a high magnetic anisotropy due to the rare earth sublat- tice. Both properties are realized in optima forma in compounds like SmCo, and Nd,Fe,,B that have found applications as important permanent magnet materials. The situation is different in intermetallics of the type R,Fe,, where the magnetic ordering temperatures as well as the anisotropies are too

Crystal and exchange fields in SmCo5 studied by inelastic neutron scattering

Abstract Inelastic neutron scattering (INS) was used to study the magnetic excitations of Sm 3+ ions in the archtypical hardmagnetic material SmCo 5 . Two inelastic magnetic lines were observed that can be interpreted as: (i) a transition within the ground state J -multiplet 6 H 5/2 and (ii) a transition from the ground state to the first excited J -multiplet 6 H 7/2 . From these two transitions we have derived the leading crystal field parameter A 20 and the exchange field B ex . Our results are compared with several earlier published results.

Nitrogen- and carbon-induced reduction of GdFe exchange coupling in Gd2Fe17 doped samples

Abstract Inelastic neutron scattering (INS) is an important experimental method for determining intrinsic magnetic parameters of magnetic materials. For the new hard magnets containing rare earth R and transition metal T ions these microscopic parameters describe for example the exchange and crystal field interactions. We have employed the INS method to determine with very good accuracy the intersublattice exchange coupling between the R ≡ Gd and T ≡ Fe sublattices in Gd 2 Fe 17 , Gd 2 Fe 17 N 2.7 and Gd 2 Fe 17 C x with x = 0.5, 1.0 and 1.5. Although it is well known that the overall magnetic properties of N- and C-doped samples are considerably better than those of the pure compound Gd 2 Fe 17 we find a drastic reduction in the Gdue5f8Fe exchange coupling in the doped samples.

Exchange fields in Gd-Fe intermetallics studied by inelastic neutron scattering

Abstract Inelastic neutron scattering (INS) was used to study the magnetic excitations in the compounds Gd 1− x Y x Fe 2 and Gd 2− x Y x Fe 14 B. Three inelastic magnetic lines were observed in the INS spectra of these compounds, the two smaller lines appearing as shoulders to the main line. From the concentration-dependent shift of the dominant magnetic line we have obtained experimental information of the strength of the Gd–Gd interaction in these materials and showed that the Gd–Gd contribution to the total molecular field experienced by the Gd moments is roughly an order of magnitude smaller than the contribution of the Gd–Fe interaction. Our results are compared with several earlier published results, including results of electronic band structure calculations.

Pressure dependence of the magnetic structures and excitations in the giant magnetostriction compound TbCu2

Abstract A small shift of magnetic excitation energies is expected when applying pressure on a compound with large magnetostriction. We were able to observe these tiny shifts by inelastic neutron scattering on the giant magnetostriction (GMS) compound TbCu 2 . The experiments were performed at 4 and 60xa0K using a McWhan pressure cell. The peaks in the spectra were shifted by 0.4xa0meV to higher energies at the maximum pressure of 2xa0GPa by the magnetoelastic interaction. This strong interaction of the crystal electric field (CF) with the lattice may be liable for the GMS effect. Moreover, neutron diffraction experiments show a weak but noticeable influence of strong external pressure on the magnetic structure of TbCu 2 . The ambient pressure magnetic propagation vector τ=( 2 3 1 0) at low temperatures is also preserved under pressure. The data indicate a non-collinear magnetic structure. In addition to the CF the exchange interaction also changes under pressure and leads to a slightly modified magnetic propagation vector in the vicinity of T N .

Commensurate magnetic structures in Er91.6%Tm8.4%

We have studied the magnetic behaviour of the alloy Er91.6%Tms.4% using ultrasound, SQUID and neutron-scattering measurements. We have found that below 40 K the magnetic structure is very similar to the magnetic phase observed between 52 and 18 K in Er. However, high-order commensurate structures, which are stable over no more than approximately 2 K in pure Er, are stable over temperature ranges of up to 17 K in this alloy. Indeed, we find that in the region 26-18 K the magnetic structure is characterised by two modulation vectors, q = 2c* and q =--f~c*. We suggest that, on cooling, the modulation of the basal plane and c-axis components of the magnetisation become decoupled at 26 K, with the modulation of the basal plane component remaining locked into a value ofqb = }c*, while the modulation of the c-axis component decreases towards a value of q~ =-~c*. At 18 K the magnetic structure reverts to a single q structure with q = ~c*.

Impurity effects on a two-leg spin ladder compound SrCu2O3

Nonmagnetic impurity effects on a two-leg quantum spin ladder with a large spin gap of about 400 K were investigated. Surprisingly, only a few % of impurity was found to drive the host gapless and antiferromagnetically ordered at a composition-dependent temperature below 10 K.