J.G.M. Armitage

The volume dependence of the magnetization and NMR of Fe4N and Mn4N

The forced volume magnetostriction and the NMR of ferromagnetic FeN and ferrimagnetic Mn4N have been measured in the ordered state. At 4.2 K the magnetization ( sigma ) per unit mass and the effective field (HI) at the nucleus of the Fe(I) site of Fe4N are found to change with pressure such that delta ln sigma / delta P approximately= delta ln mod HI mod / delta P 0. The result for Mn4N is interpreted as showing that the magnitude of the small (negative) moment on the Mn(II) site decreases more rapidly under pressure than does the large Mn(I) moment. The value of delta ln mod HI mod / delta P for Mn4N was found to be a strong function of temperature such that delta lnTN/ delta P approximately=5.2 Mbar-1. An analysis of the Mn4N NMR data suggests that the discrepancy between the calculated (spin) and measured moment at the Mn(I) site may be due to a small orbital moment at that site.

The magnetic moment at the yttrium site in Y-Fe compounds: pressure dependence of the magnetisation and hyperfine field

The pressure dependence of the magnetisation of Y2Fe17, Y6Fe23 and YFe2 at 4.2 K has been deduced from forced volume magnetostriction measurements in fields up to 12 T. The pressure dependence of the 89Y hyperfine field in the above compounds and YFe3 has been measured using NMR. The results are consistent with a model in which a moment of approximately=-0.4 mu B exists at the Y site of all four compounds as found in computer calculations for YFe2.

Volume magnetostriction and pressure dependence of the Curie point and spontaneous magnetization of weakly ferromagnetic Y(Co1-xAlx)2

The pressure dependence of the Curie point of weakly ferromagnetic Y(Co1-xAlx)2 alloys for x approximately 0.15 has been measured at pressures up to 8 kbar. The pressure dependence of the spontaneous magnetization per unit mass at 0 K ( sigma 0) has been deduced for the same alloys from measurements of the forced volume magnetostriction in fields up to 12 T. It was found that ( delta ln Tc/ delta ln V)=( delta ln sigma 0/ delta P)=120+or-17, one of the largest values known for a ferromagnetic material. The critical pressure for the collapse of ferromagnetism is approximately 9+or-1 kbar for 0.14<x<0.18, while the chemical pressure exerted by the Al in Y(Co0.85Al0.15)2 is approximately -40 kbar, so weak ferromagnetism would not be possible in this Y-Co-Al system if the material was clamped to the volume of YCo2.

Low-temperature thermal and high-pressure studies of CePd and

The anomalous properties of the Kondo lattice are compared with the well behaved Kondo system, CePd. The low-temperature thermal expansion of CePd is in agreement with previous heat capacity data, showing a ferromagnetic transition at and a second transition at 3.5 K probably due to reorientation of the magnetic moments. The Gruneisen factor, calculated from thermal-expansion and heat capacity is , the same as the Gruneisen factor calculated from the pressure dependence and comparable to a previous measurement of . Thermal expansion measurements (in fields of up to 8 T) and ac susceptibility measurements (under pressures of up to 7.33 kbar) have been made on in the temperature range 1.6-40 K. The zero-pressure ac susceptibility measurements confirm that there is an antiferromagnetic transition at , as previously reported. The magnetic contribution to the linear thermal-expansion coefficient of polycrystalline in zero magnetic field has a maximum value near 17 K and becomes small by 29 K. There is no peak in at the Neel temperature. The Neel temperature is found to decrease under pressure at the rate of , which indicates that is a magnetic Kondo lattice (with ) on the right-hand side of the Doniach diagram.

A ferromagnetic Kondo compound: CePdSb

Abstract The ferromagnetic ground state of CePdSb has been confirmed by neutron diffraction measurements and the observation of Sb-NMR in zero field. It is therefore one of the few ternary compounds to exhibit both Kondo lattice and ferromagnetic behaviour. Inelastic neutron scattering has allowed the crystal field parameters of the cerium ion to be determined. Under pressure the Curie point ( T c ≅ 17 K) of CePdSb was found to increase at the rate d ln T c /d P = 14 Mbar −1 .

Pressure dependence of magnetic properties of Fe4N and Mn4N

Abstract The value of the magnetization of ferromagnetic Fe 4 N is found to decrease under pressure while that of ferrimagnetic Mn 4 N increases. The magnitude of the effective field at the 55 Mn nucleus of the Mn(I) site of Mn 4 N also increases under pressure. It is deduced that the magnitude of the moment at the Mn(II) site decreases under pressure, while that of the Mn(I) site is independent of pressure, in agreement with the model of covalent magnetism for Mn 4 N.

Pressure dependence of magnetic properties of Nb1−yFe2+y

Abstract The pressure dependence of magnetic properties was investigated in antiferromagnetic (stoichiometric) and ferromagnetic (off-stoichiometric) NbFe2 with the C14 Laves phase structure.

Evidence for a magnetic moment at the Lu site of LuFe2

Abstract High pressure 175 Lu NMR measurements of LuFe 2 at 4.2 K suggest that Lu, like Y and Zr, carries a negative magnetic moment, in agreement with self-consistent energy band calculations. The observed spectrum is more complicated than would be expected for a Laves phase compound.

Forced magnetostriction and pressure dependence of the magnetism of weakly ferromagnetic Y(Co1−xAlx)2 and Sc3In

The Curie point and spontaneous magnetization of weakly ferromagnetic Y(Co1−xAlx)2 alloys with x∼0.15 is shown to decrease rapidly with increasing pressure, in agreement with the theory of weak itinerant ferromagnetism. Forced magnetostriction measurements on Sc3In, however, confirm that the magnetization at 4.2 K in a field of ∼2 T increases with pressure.

Thermal expansion and NMR of CePdSb

Abstract The thermal expansion coefficient of polycrystalline CePdSb shows no feature at the Curie point (17 K) but a broad peak near 10 K, in agreement with earlier measurements of the magnetic heat capacity. Single-crystal measurements show that the thermal expansion coefficient of the magnetically hard c direction is an order of magnitude greater than that of the a or b direction. The temperature dependence of the zero external field Sb NMR does not show any unusual behaviour near 10 K.