Magnetic Hysteresis Effect Of Magnetoresistance Effects

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An initial resistance versus magnetic field measurement on NdMo16O44 reveals a pronounced magnetic hysteresis effect when a magnetic field is applied perpendicular to the current, but with unknown orientation with respect to the crystal axes, as shown in Fig. 2a for temperatures from 12K to 30K (at temperature below 12K, the overall resistance is too high to produce low-noise measurements with resolvable magnetoresistance features). The individual plots are offset to better show the effect. A sharp drop in the magneto-resistance on the order of 30% of the zero-field resistance appears at a temperature of 12K, with local extrema at fields of approximately +0.38T and +0.55T (-0.38T and -0.55T, respectively) when the field is swept from
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The percent change in the resistance of these features decreases as temperature is increased, disappearing above 30K. A positive magnetoresistance feature can also be seen centered at approximately ±0.75T for temperatures of 28K and 30K.. The origin of these magnetoresistance effects is unclear, as NdMo16O44 contains magnetic Nd ions. The paramagnetism associated with Nd-Nd interactions confounds the measurement of the magnetization associated with Mo8-Mo8 interactions―the focus of this paper―resulting in the predominantly paramagnetic magnetic susceptibility behavior for NdMo16O44 shown in Fig. 2b. In contrast, LaMo16O44, demonstrates a more interesting magnetic susceptibility versus temperature profile that demands further investigation. It is important to note that La is a non-magnetic rare earth, meaning that any observations of magnetic ordering in LaMo16O44 are expected to arise from Mo8-Mo8 cluster …show more content…
2c demonstrate substantial charge transport between metallic moieties, likely via hopping, with room temperature resistivities of approximately 2 Ω·cm and 4 Ω·cm, respectively. As the temperature is lowered, the resistivity increases exponentially for both LaMo16O44 and NdMo16O44, respectively, signifying a decrease in the charge transport between Mo8O36 moieties and an overall semiconducting/insulating behavior in these materials. Below 5K, the sample resistance in the NdMo16O44 sample becomes prohibitively high and unmeasurable, whereas at these temperatures, the LaMo16O44 sample has a resistance that permits transport measurements down to a temperature of 2K. The plateau in the resistivity of LaMo16O44 at zero magnetic field and temperatures below 5K indicates a temperature-independent conductance mechanism in this material.
With a magnetic field applied perpendicular to the current (but unknown orientation with respect to the crystal axes), the resistance versus temperature plot reveals a notable magnetic field effect―a local maximum in the resistance versus temperature with a peak around 6 K―that increases in magnitude with increasing magnetic field. The sample resistance is independent of temperature up to about 6K, and then starts to drop; and the resistance can be modeled with a phenomenologically derived logistic function for resistance versus 1/T (Fig.

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