Magnetic Characterisation

Magnetic CharacterisationAn atom possess a magnetic moment that can act cooperatively with that of its neighbours to form a magnetically ordered ground state. These ground states may be broadly classified by whether the magnetic moments of neighbouring atoms align or anti-align, either with each other or with an externally applied magnetic field. Perhaps one of the most important criteria for characterising these phenomena is the temperature at which these cooperative effects emerge – the transition temperature. The temperature at which thermal energy/fluctuations become less than the exchange coupling is a function of environmental conditions such as applied magnetic field, electron doping and pressure. When taken together these may be composed into a magnetic phase diagram, which we can compose using experiments such as SQUID magnetometry, vibrating sample magnetometry (VSM) or AC susceptibility. These techniques - along with other probes such as neutron scattering, electron spin resonance and magnetic X-ray scattering - provide both a bulk and microscopic magnetic characterisation of a material.

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Figure: Complete phase diagram of the metal-organic compound (C5H12N)2CuBr4, including the spin Lutinger Liquid (LL) phase, which has fractional spin excitations. [courtesy Christian Ruegg]