engleski

Torque magnetometry as a sensitive probe for measuring magnetic anisotropy in paramagnetic and magnetically ordered states of magnetic systems

Torque magnetometry is an experimental method that probes bulk magnetic anisotropy of a magnetic sample. Measured magnetic torque gives most informative results when single crystalline samples are available. In this work some advantages of torque magnetometry over standard magnetometry measurements will be presented. An application of highly sensitive low-field (H<1T) torque magnetometry is presented on several spin S=1/2 systems with small magnetic anisotropy which comes mainly from the anisotropy of the electron g factor. In the paramagnetic sample magnetic torque is proportional to the magnetic susceptibility anisotropy, and thus represents a much more sensitive method for measuring magnetic anisotropy than e.g. measurement of susceptibility by standard magnetometry methods. This turns out to be relevant in S=1/2 systems where anisotropic exchange interaction is present, such as 1D S=1/2 Heisenberg antiferromagnet with Dzyaloshinskii-Moriya interaction. Torque magnetometry can routinely detect the rotation of magnetic axes with temperature and in combination with electron spin resonance (ESR) spectroscopy this rotation can be correlated to the temperature change of the g tensor. Symmetry of the magnetically ordered states can also be determined by torque, as will be shown on examples of antiferromagnetically ordered systems with easy plane and cubic anisotropy and uniaxial ferromagnet. In collinear uniaxial antiferromagnet reorientation of the spin axes influences angular dependence of torque in magnetic field H smaller than the spin flop field H_{;SF};. This allows the determination of the value of spin flop field in H< H_{;SF};, which gives torque magnetometry an advantage over standard magnetization measurements. Probing magnetic symmetry with torque can be used as an alternative when standard methods such as e.g. neutron scattering cannot be employed.

Torque magnetometry; magnetic anisotropy

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