Ti NMR Study of the Nearly Ferromagnetic System TiBe2

Abstract

NMR data on TiBe 2 have been taken from 1.3 to 270 K in magnetic fields up to 60 kG. The linear dependence of the Knight shift and the NMR linewidth with x = M/H show that the increase of x versus applied field at low temperatures is due to a homogeneous property of the electron gas. The ^-electron contribution to the spin-lattice relaxation rate is found to scale linearly with \T in a wide temperature range spanning the spin-fluctuation temperature.PACS numbers: 76.60. Cq, 75.20.En, 76.60.Es The properties of the intermetallic compound TiBe 2 have attracted considerable interest in recent years. This cubic C-15 type material has a strongly enhanced, temperature-dependent susceptibility 1 ' 2 and at low temperatures the x~M/H susceptibility changes with the magnetic field 3 ' 4 and shows a maximum at about 50 to 60 kG. The large enhancement of the susceptibility without any long-range magnetic ordering at low temperature, together with the specific heat, resistivity, 5 * 6 and ESR data 7 show that the electronic system in TiBe 2 exhibits the properties of an interacting Fermi liquid with a low spin-fluctuation temperature 8 (T sf ~ 20 to 50 K). The consequences of the interactions on a microscopic scale, the behavior of the dynamic susceptibility, and the origin of the field-dependent x are open problems which call for more experimental work. On the other hand, the influence of sample preparation on some macroscopic properties, such as the magnitude of the maximum of M/H 9 is apparent in the early publications. 3 * 4 More systematic investigations as a function of preparation techniques are presently attempted. 6 It is quite important to determine whether the differences in the macroscopic parameters are induced mainly by homogeneous modifications of the electronic structure, by sample inhomogeneities, or by local environment effects around impurities. NMR as a microscopic probe is well suited to clear up this point and to provide information on the dynamical susceptibility through nuclear relaxation measurements.In this Letter we present NMR investigations on the Ti nuclei in a wide range of fields and temperatures. The TiBe 2 sample was prepared by Monod et al. A and before reduction into powder for the NMR measurements it has been heat treated in vacuum at 800 K for 100 h. The resistivity ratio r = p(300 K)/p(4.2 K), the low-field susceptibility x (10 kG), and the susceptibility ratio £ = x(60kG)/x(10kG) were r=36, x(10) = 8.4 x 10 " 3 emu/mole, and/> = 1.18, respectively, after annealing. On the other hand r = 110, x(10) = 9.7xl0" 3 emu/mole, and/? = 1.27 were found on a sample prepared in Los Alamos, which confirms the different results of Refs. 3 and 4 and shows that our sample is adequate for investigating any problem linked with sample homogeneity.The NMR spectra were taken with a phase-coherent spectrometer operating at a fixed frequency in the range from 5 to 16 MHz. The magnetic field was calibrated by measuring the NMR signal of 109 Ag in a silver sample 9 located in the same sample holder as the T...

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