An MNP machine provides a bias field consisting of a low frequency alternating magnetic field and possibly a static magnetic field to a volume in possibly different directions; RF drive coils driven at an FMR/EPR frequency of MNPs in the bias field, and pickup coils or magnetometers measuring the magnetization induced in the MNPs by the bias fields and possibly the RF absorption. The computer derives MNP MPS/MSB spectra, magnetic particle images, or heats the MNPs using the EPR/FMR frequency field. A method of imaging or localizing the MNPs includes applying a magnetic field gradient; applying RF at an EPR/FMR frequency of the MNPs; sweeping magnetic bias field strength or RF frequency to sweep a resonance surface; applying RF at the EPR/FMR frequency, observing EPR/FMR resonances; rotating the magnetic bias field relative to the subject and resweeping the surface; and reconstructing a three-dimensional distribution of MNPs.

A structure includes a negative temperature coefficient (NTC) resistor for use in gallium nitride (GaN) technology. The NTC resistor includes a p-type doped GaN (pGaN) layer, and a gallium nitride (GaN) heterojunction structure under the pGaN layer. The GaN heterojunction structure includes a barrier layer and a channel layer. An isolation region extends across an interface of the barrier layer and the channel layer, and a first metal electrode is on the pGaN layer spaced from a second metal electrode on the pGaN layer. The NTC resistor can be used as a temperature compensated reference in a structure providing a temperature detection circuit. The temperature detection circuit includes an enhancement mode HEMT sharing parts with the NTC resistor and includes temperature independent current sources including depletion mode HEMTs.

A nanoscale temperature detector including a diamond sensing probe with a transverse dimension of at least 200 nanometres and a sensing tip-having a curvature radius of less than 100 nanometres, less than 10 nanometres or less than 1 nanometre, and a plurality of colour centres, whose emission count rate show temperature-sensitive features. The diamond sensing probe has a transverse dimension of at least 200 nanometres and is connected to a to a detector system by means of a mounting structure. A thermal isolation barrier thermally decouples the sensing probe from the detector system.