Principles and performance of a high-field time domain magnetic spectrometer

Abstract

A time domain magnetic spectrometer based on a pick-up coil is presented for the study of spin-lattice relaxation rates in paramagnetic samples at high magnetic fields and at liquid-helium temperatures. The equilibrium between the spin system and the lattice is disturbed either by heating the spin system under the electron spin resonance condition (using far-infrared laser pulses) or by heating the lattice (using nonresonant laser pulses). Resulting magnetization changes induce a voltage in a pick-up coil oriented parallel to the field. By measuring the temporal evolution of this voltage, one can observe the spin-lattice relaxation directly. The spin-lattice relaxation in the diluted magnetic semiconductor CdMnTe is measured in order to demonstrate the performance of the spectrometer. The two methods of disturbing the equilibrium between the spin system and the lattice are compared.

Spin-Lattice Relaxation Beyond the Debye Approximation

“…Our experimental method is based on heating the lattice with far infrared (FIR) laser pulses [4]. The spins then warm up to reach thermal equilibrium with the "hot" lattice.…”

“…The spins then warm up to reach thermal equilibrium with the "hot" lattice. Because magnetization in our system is given by the spin alignment (paramagnetic sample), changes of the spin states appear as magnetization changes and are detected with a pick-up coil [4]. Several FIR laser lines were used to ensure that the results are not photon energy dependent.…”

Unusual Time Dependence of Magnetization Relaxation in MBE Grown Epilayer of CdMnTe

“…These changes induced a voltage in the pick-up coil. For the bulk crystals the amplitude of the induced voltage after a sharp rise at the beginning decays exponentially (spin-lattice relaxation time) [4,5]. Sometimes the decay is described by the sum of a few exponential functions, but is always monotonic.…”

“…We measured the magnetization relaxation using the nonresonant method described in [5]. After a short laser pulse that warms the lattice, the spin system warms up to the new temperature by means of spin-lattice relaxation [4], changing the sample magnetization (given by the spins' alignment).…”

Orientation Dependent Spin-Lattice Relaxation in CdMnSe

“…PACS numbers: 76.30.Fc, 63.20.Dj Using the nonresonant technique described earlier [1], we measured the magnetization dynamics in Cd1-xMnxSe at 4.5 K as a function of magnetic field. Two different compositions were investigated, namely x = 0.01 and x = 0.02.…”