Polarization of a paramagnet by a fast high intensity magnetic field pulse : spin and phonon relaxation, phonon spectroscopy

2014 The low temperature transient response of the polarization of a paramagnet to a fast high intensity (1 ms; 250 kG; 1/2 sine-wave) field pulse is shown to give information on spinlattice coupling, density and relaxation of phonon modes and, sometimes, magnetic ordering temperatures. LE JOURNAL DE PHYSIQUE TOME 35, DÉCEMBRE 1974, Classification Physics Abstracts 8.630 An analysis of the response of the magnetization to a fast 2 wave sinusoidal field pulse can give very direct information on : i) the field dependence of the spin-phonon coupling ; ii) the spectral density of phonon modes ; iii) the phonon relaxation ; iv) the magnetic ordering of the paramagnet. FIG. 1. Form of magnetic field pulse. u represents magnetic field normalised to H maximum. To illustrate, we take the classic example of CuK2(S04)2 6 H20 a simple system on which paramagnetic resonance [1] and relaxation [2] experiments have been done. Figure 2 shows the experimentally FIG. 2. Response of the polarization of CuK2(S04)2 6 H20 at 4.2 K to field pulse of figure 1 with H maximum = 250 kG. The crosses (+) are experimental points transcribed from a photograph of the oscilloscope trace. Curve A is best fit of eq. (6) relaxation without bottleneck-and curve B is best fit of eq. (7) bottleneck